Assessment of Electric and Magnetic Field Exposure from Power Generation for Energy UK

Transcription

1 CRCE/NIR/5/639 Assessment of Electric and Magnetic Field Exposure from Power Generation for Energy UK N A Cridland, A J Lowe, F M Petty, N Northrop and S Jakes Commercial-in-confidence Contract Report

2 Centre for Radiation, Chemical and Environmental Hazards Public Health England Chilton, Didcot Oxfordshire OX11 0RQ Crown Copyright 2016

3 CRCE/NIR/5/639 Assessment of Electric and Magnetic Field Exposure from Power Generation for Energy UK N A Cridland, A J Lowe, F M Petty, N Northrop and S Jakes EXECUTIVE SUMMARY Energy UK commissioned an assessment of potential hazards arising from exposure of staff to electromagnetic fields whilst working at power generation plant. Power stations are normally large sites with equipment generating high voltages and high currents, which in turn result in strong electric and magnetic fields. In addition to generators, transformers, conductors and switch gear, such sites normally also operate a wide range of ancillary equipment ranging from large pumps and fans to plant for cleaning flue gasses. The results of all measurements were compared with the action levels in the Control of Electromagnetic Fields at Work Regulations 2016 and the specified in the European Council Recommendation 1999/519/EC. The work was undertaken between May and August Only two situations were identified that could give rise to whole body exposures at or in excess of the high action levels. One of these was close to the neutral point beneath a generator, whilst the second was close to generator exciter cables running up an enclosure for an exciter transformer. In both cases, the strong fields were highly localised and it should be straightforward to restrict access when equipment is in operation. It was identified that the low action levels for electric field strength could be exceeded within banking compounds. No other situations identified that would result in whole body exposures in excess of the low or high action levels. Field strengths in excess of the low action levels were measured in a small number of other situations, but were restricted to volumes too small to result in whole body exposures. A larger number of areas were identified where electromagnetic fields may be strong enough to present a risk to employees at particular risk as identified in the new legislation. Some of these areas, such as transformer compounds and switch rooms, have restricted access anyway. The strong fields generated around static converter cabinets during start-up of gas turbines are generally present for only a few minutes and these cabinets may well be located in areas with restricted access such as switch rooms. For other areas such as close to This report was prepared under contract with Energy UK. Centre for Radiation, Chemical and Environmental Hazards Public Health England Chilton, Didcot Oxfordshire OX11 0RQ Crown Copyright Approval: November 2016 Publication: November 2016 This report from the PHE Centre for Radiation, Chemical and Environmental Hazards reflects understanding and evaluation of the current scientific evidence as presented and referenced in this document.

4 generators, generator exciter systems and the isolated phase bus from the generator, it should be straightforward to implement access restrictions. These restrictions would also apply during activities such as live brush changing. However, in some areas, such as beneath outgoing conductors or above underground conductors, effective restriction of access may be more difficult to achieve. In this context it is relevant to consider the nature of access restrictions for employees at particular risk. Those with active implants or body-worn medical devices are at risk of device malfunction during even transient exposure. Hence these individuals should not enter any area where whole body exposures in excess of the are possible unless it can be shown that the particular device on which they rely is not susceptible to interference at the field strengths present in that area. Localised strong fields may also present a risk if it is foreseeable that they could give rise to exposure of the device. Hence these employees should also keep away from equipment capable of generating localised strong fields, such as motors used to drive pumps and fans. The situation for those with passive implants and pregnant women is somewhat different. Passive implants may result in localised field enhancements, but in the absence of sharp points on the implant these are unlikely to be large. Implants may also be subject to inductive heating, the magnitude of which will depend on a number of factors. However, even if inductive heating is likely to be significant, it will take time for the temperature of the surrounding tissue to rise so that simply passing through an area is unlikely to result in harm. Similarly for pregnant women, any adverse effect on the fetus would require prolonged exposure and passing through an area is unlikely to result in harm. Table ES1 summarises the principal findings from the surveys. It should be noted that this table is provided as a guide to situations that may require further consideration. Where action or are shown as having been exceeded, this will not necessarily have been the case in all stations and more detailed information may be found in the detailed results from individual surveys that are given in Appendices C H. Table ES1 Summary of findings from surveys Compliance Low action levels Reference levels Actions required for: Employees not at particular risk Employees at particular risk (excluding active implants and bodyworn devices) Employees with active implants or bodyworn medical devices Generators Pilot exciter Yes No* No No Yes Main exciter / brush gear Yes No No Yes Yes Exciter / AVR cabinets Yes No No Yes Yes ii

5 Table ES1 Summary of findings from surveys Compliance Low action levels Reference levels Actions required for: Employees not at particular risk Employees at particular risk (excluding active implants and bodyworn devices) Employees with active implants or bodyworn medical devices Exciter transformer No No Yes Yes Yes Excitation disconnection switch Yes No No Yes Yes Walkways around sides of stator Yes Yes No No No Non-drive end of stator Yes No No Yes Yes Neutral earth point No No Yes Yes Yes Static frequency converter (during gas turbine start-up) Yes No No No Yes Power distribution Isolated phase bus Yes No No Yes Yes Generator transformer compound (inside) Yes No No Yes # Yes Generator transformer compound (outside) Yes Yes No No No Unit auxiliary transformer Yes No No Yes # Yes Station transformer Yes No* No No Yes Other transformers Yes Yes No No No 11 kv switch rooms Yes No* No No Yes 6.6 kv switch rooms Yes No* No No Yes 3.3 kv switch rooms Yes Yes No No No 415 V switch rooms Yes No* No No Yes Phase conductors from generator transformer Yes No No Yes # Yes Banking compounds (inside) No No Yes Yes # Yes Banking compounds (outside) Yes Yes No No No National Grid Substations (outside) Yes Yes No No No Outgoing conductors Yes No No Yes Yes iii

6 Table ES1 Summary of findings from surveys Compliance Actions required for: Low action levels Reference levels Employees not at particular risk Employees at particular risk (excluding active implants and bodyworn devices) Employees with active implants or bodyworn medical devices Ancillary equipment Pump motors Yes No* No No Yes Fan motors Yes No* No No Yes Precipitators Yes Yes No No No Conveyors Yes Yes No No No Tramp metal screens No n/a Yes Yes Yes Vibratory feeders Yes Yes No No No * Over a highly localised region only, so whole body exposures unlikely May also exceed high action level Exposure for very limited duration only Generally localised, but region may be around 1-2 m - whole body exposures possible # Need to consider time spent in area where are exceeded Based on very limited data comparison with data from other switch rooms suggests that localised areas in excess of might be found in more a more extensive survey Exceeds indirect effects action levels for interference with active implanted medical devices and projectile risk The survey included equipment associated with the generation and distribution of electrical power within stations, but did not include elements of station infrastructure such as electric fences or tools such induction heaters that may be used to free seized bolts or bearings. iv

7 CONTENTS Executive Summary i 1 Introduction 1 2 New Legislation 1 3 Description of Facilities Assessed Power Stations Surveyed Aberthaw Power Station Connah s Quay Power Station Didcot B Power Station Drax Power Station Heysham 2 Power Station Staythorpe Power Station 3 4 Measurement Equipment and Results 3 5 Risk Assessments Operation of Generators Routine Generation Description of Activity Summary of Exposures Electric fields Magnetic fields Assessment of Exposures Electric fields Magnetic fields Control Measures Triggers for Reassessment Operation of Generators Other Operational Activities Description of Activity Summary of Exposures Electric fields Magnetic fields Assessment of Exposures Electric fields Magnetic fields Control Measures Triggers for Reassessment Power Distribution Description of Activity Summary of Exposures Electric fields Magnetic fields Assessment of Exposures Electric fields Magnetic fields Control Measures 11 v

8 5.3.5 Triggers for Reassessment Ancillary Equipment Description of Activity Summary of Exposures Electric fields Magnetic fields Assessment of Exposures Electric fields Magnetic fields Control Measures Triggers for Reassessment 13 6 Discussion Exposures in Excess of the Action Levels Exposures in Excess of the Reference Levels 15 APPENDIX A Legislation and Guidance 17 APPENDIX B Measurement Equipment and Survey Methods 29 APPENDIX C Measurement Results Aberthaw Power Station 31 APPENDIX D Measurement Results Connah s Quay Power Station 45 APPENDIX E Measurement Results Didcot B Power Station 61 APPENDIX F Measurement Results Drax Power Station 75 APPENDIX G Measurement Results Heysham 2 Power Station 87 APPENDIX H Measurement Results Staythorpe Power Station 103 vi

9 DESCRIPTION OF FACILITIES ASSESSED 1 INTRODUCTION Energy UK is the trade association for the UK energy industry representing over 80 suppliers and generators of electricity and gas for domestic and business consumers. Its members operate power stations across the UK and need to consider the implications of the new Control of Electromagnetic Fields at Work Regulations 2016, which implement the Electromagnetic Fields Directive (2013/35/EU) within the UK. To inform the consideration of risks from exposure to electric and magnetic fields, Energy UK contracted Public Health England s Centre for Radiation, Chemical and Environmental Hazards to assess exposure to electric and magnetic fields at a sample of six power stations, selected to be representative of different types of power generation plant currently in operation in the UK. The results of this assessment should provide an indication to Energy UK s members of the types of equipment and activities that may need to be considered in relation to compliance with the new regulations. The surveys on which this assessment is based were carried out between May and August So far as possible data were obtained for generators operating at maximum output, subject to the constraints of making measurements in operational commercial power stations, many of which continuously adjust output according to demand. 2 NEW LEGISLATION The Control of Electromagnetic Fields at Work Regulations came into force in July These regulations implement the EMF Directive (Directive 2013/35/EU) in the UK and introduced a number of new requirements. Given the nature of the equipment and activities described in Section 3, these regulations will apply to work at power generation facilities operated by members of Energy UK. The requirements of these regulations are discussed in more detail in Appendix A. The EMF Directive placed a duty on the European Commission to publish a practical guide to achieving compliance and Public Health England wrote this on behalf of the Commission. 3 DESCRIPTION OF FACILITIES ASSESSED 3.1 Power Stations Surveyed A sample of six power stations was selected by Energy UK as representative of typical power plant currently in use in the UK. The stations selected were: Aberthaw Connah s Quay Didcot B Drax 1

10 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Heysham 2 Staythorpe A brief description of each station is given below Aberthaw Power Station Aberthaw was constructed as a coal-fired power station and began operation in Although Aberthaw still burns semi-anthracitic low volatile coal as its principal energy source, recent investment has included construction of a biomass facility to enable the co-firing of sawdust and woodchips that supply up to 55 MW into the main plant. It has a total generating capacity of just over 1.5 GW of electricity from three 520 MW units. The power station was designed and manufactured by General Electric Company. Aberthaw is equipped with a Flue Gas Desulphurisation (FGD) plant that uses seawater to convert sulphur dioxide into sodium sulphate and calcium sulphate and a precipitator to remove fine particulates from flue gasses Connah s Quay Power Station Connah s Quay was constructed on the site of a former coal-fired power station as a modern combined cycle gas turbine (CCGT) station burning natural gas and began operation in It has a total generating capacity of 1.32 GW generated by four 330 MW units. Each unit consists of one gas and one steam turbine on a single shaft. It was built by Alstom based on its 9F design Didcot B Power Station Didcot B is a modern CCGT power station burning natural gas that began operation in It has a total generating capacity of 1.36 GW generated by two 680 MW units. Each module consists of two 230 MW gas turbines and a single steam turbine. It was constructed by Siemens based around its V94.3 design Drax Power Station Drax has the greatest generating capacity of any power station in the UK with a total generating capacity of 3.96 GW. It was constructed in two phases as a coal-fired station and began operating in Although it still burns coal, the station has been co-firing biomass and coal since 2004 and one unit has now been fully converted to biomass. The station consists of six 660 MW units. The generators were manufactured by Parsons based on its 660 MW design. Drax employs boosted over fire air (BOFA) to reduce nitrogen oxides emissions and is equipped with a precipitator to remove fine particulates from flue gasses Heysham 2 Power Station Heysham Power Station is a nuclear power station operated by EDF Energy. The site is divided into two separately-managed stations, Heysham 1 and Heysham 2, both of the advanced gas-cooled reactor (AGR) type. Heysham 2 opened in 1988 and has a generating 2

11 RISK ASSESSMENTS capacity is 1230 MW. It has two reactors and turbine generators, which are referred to as Units 7 and Staythorpe Power Station Staythorpe is a modern CCGT station burning natural gas that began operation in It has a total generating capacity of 1.65 GW, generated by four 430 MW units. Each module consists of a 288 MW gas turbine and a steam turbine. The station was built by Alstom based on its GT26 design. 4 MEASUREMENT EQUIPMENT AND RESULTS The equipment and techniques used for the surveys are described in Appendix B. Measurement results are presented in: Appendix C Aberthaw Power Station Appendix D Connah s Quay Power Station Appendix E Didcot B Power Station Appendix F Drax Power Station Appendix G Heysham 2 Power Station Appendix H Staythorpe Power Station 5 RISK ASSESSMENTS 5.1 Operation of Generators Routine Generation Description of Activity Generators are normally installed in a generator hall and typically have an access walkway that extends around the non-drive end and along the sides of the generator. In addition, there may be some access beneath the generator. In order to generate the static magnetic field required for power generation, each generator has an excitation system. Power for the excitation system normally comes either from the main stator output (self-excited) or from a small self-excited or permanent magnet generator located at the non-drive end of the generator. Excitation current is rectified and fed into the generator rotor, normally via a brush and slip-ring arrangement at the non-drive end of the generator. Excitation current is controlled by the automatic voltage regulator (AVR) in order to maintain a constant voltage output from the generator. The output from the generator is fed into an isolated phase bus (see Power Distribution) via the generator terminals. Generator terminals are generally at either the top or bottom of the generator and each connects to a separate phase winding in the stator. The other ends of the 3

12 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK phase windings are normally connected at the star point, which is indirectly connected to earth, via a transformer, reactor or resistor Summary of Exposures Electric fields There are no exposed high voltage conductors in the area around the generator and electric fields will normally be contained within the insulating medium surrounding conductors. Consequently there is no expectation of strong electric fields Magnetic fields Strong magnetic fields are generated in the vicinity of the generator stator and exciter brush gear. These fields should not exceed the low action levels at any normally accessible position although they are likely to exceed the Council Recommendation close to the generator. In some cases magnetic flux densities may exceed the by a considerable margin and remain above the across the entire width of the access walkway around the generator. Strong magnetic fields are also generated around the excitation systems. Rectification of the exciter current generates components at high frequencies where the action and reference levels are more restrictive. In one case magnetic flux densities exceeded both the low and high action levels to distances of up to 0.4 m from cables running down the outside of the transformer enclosure. Any similar situation is likely to produce the same result. In all surveys magnetic flux densities exceeded the Council Recommendation by a considerable margin. Strong magnetic fields may be generated in the vicinity of the generator main terminals, although these are not usually accessible during normal running. Where access is possible, for example when terminals are located beneath the generator, magnetic flux densities should not exceed the low action levels, but may exceed the Council Recommendation reference levels by a considerable margin. In one case strong fields were also measured in the vicinity of the generator neutral point, where exposure at the high action levels was possible Assessment of Exposures Electric fields There are no exposed high voltage conductors in these areas and consequently no source for strong electric fields. There is no requirement to make any further assessment of exposures in these situations Magnetic fields Accessible magnetic fields measured around the non-drive end of the generator stator were typically around % of the. Fields were lower around exciter brush gear, typically around the, although the highest value measured was 190% of the. 4

13 RISK ASSESSMENTS Strong fields were measured in the vicinity of rectifiers, transformers, and automatic voltage regulators associated with generator excitation systems. The strongest field was measured around cables running down the outside of an exciter transformer enclosure and represented 150% of the high action levels. The region over which the high action levels were exceeded extended for 0.35 m from the cables and was therefore just large enough to get a body into. Magnetic flux densities at the surface of the cable also exceeded the limb action levels. Fields around other excitation equipment did not exceed the action levels, but were generally well in excess of the, with the maximum measured field representing 700%. Fields in excess of the typically extended across access walkways around the equipment. At Staythorpe an isolated phase bus was used to take the neutral ends of the generator stator windings to the neutral point beneath the generator. Strong fields measured in the vicinity of this installation were around 100% of the low and high action levels. At Aberthaw the generator terminals connected to the isolated phase bus in an interlocked enclosure beneath the generator. Magnetic flux densities at the door represented 450% of the and remained above the to the top of the access stairs, approximately 2 m from the door Control Measures For any area close to an exciter transformer where the high action levels are exceeded, access must be restricted whilst the excitation system is operational. This was observed only at Didcot B so is not likely to be a widespread issue, but may arise at other stations where similar excitation systems are installed. At Didcot it would be appropriate to restrict access to an area extending to at least 0.4 m in all directions from the cables running down the outside of the transformer compound. There may be some site to site variability, but this is unlikely to be large. Hence to avoid the necessity of surveying other sites with similar systems, it should be sufficient to adopt a conservative exclusion zone of say 0.8 m in all directions. Given that this is likely to affect only a small area, this could be achieved either by extending the transformer enclosure, or by means of suitable floor markings. For any area around the generator neutral point where exposure at the high action levels is possible, access must be restricted whilst the generator is in operation. At Staythorpe, the station where this was observed, an exclusion zone of 0.6 m from the conductors, would be sufficient and in practice was already demarcated by means of physical barriers and gates (Figure 1) so that access restriction should be straightforward to achieve. If similar situations occur at other stations, then to avoid the necessity of further surveys it should be sufficient to adopt a conservative exclusion zone of say 1.2 m in all directions. 5

14 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Figure 1 Area around the generator neutral point at Staythorpe Power Station where strong fields were measured In the absence of a person-specific individual assessment, employees at particular risk should be excluded from access to generators, generator terminals, isolated phase bus systems and all parts of generator excitation systems whenever this equipment is operational Triggers for Reassessment These include any new or modified designs for excitation systems. 5.2 Operation of Generators Other Operational Activities Description of Activity This section considers two activities that are undertaken routinely, but only for relatively short periods. The first activity is start-up, typically of a gas turbine generator, which is a procedure that usually lasts a few minutes. The second activity is live changing of exciter brushes, which is normally a planned maintenance activity occurring relatively infrequently. During start-up of a gas turbine generator, power is fed into the generator so that it is temporarily used as a motor to drive the turbine. When the turbine reaches operating speed, it is fired and the generator reverts to generation. As the generator has to accelerate from barring speed to full operational speed, a static frequency converter is used to change the frequency of the drive current. This uses thyristors to achieve the frequency shift and in doing so it generates field components at high frequency where the action and are 6

15 RISK ASSESSMENTS more restrictive. It is understood that the load on the static frequency converter is highest during the initial phase of start-up and tails off as the generator reaches full operational speed. The brushes on the excitation systems wear and require periodic replacement. This may be undertaken live so that there is no requirement to stop the generator. This activity will involve work in close proximity to the exciter conductors and in particular limb exposure essentially in contact with the conductors Summary of Exposures Electric fields There are no exposed high voltage conductors in the areas around either the static frequency converter or exciter brushes and consequently no expectation of strong electric fields Magnetic fields During turbine start-up the static frequency converter cabinets may generate strong magnetic fields with a wide range of frequency components. There was no evidence that the low action levels would be exceeded, but for the start-up assessed, the Council Recommendation were exceeded up to 0.6 m from the surface of the cabinets. For the sites assessed, there was no evidence that accessible fields around the exciter brushes exceeded the low action levels, or that magnetic flux densities in contact with the exciter cables exceeded the limb action levels implying that limb exposures should be compliant during live brush changes. Fields around the exciter cables may exceed the Council Recommendation by a considerable margin Assessment of Exposures Electric fields There are no exposed high voltage conductors in these areas and consequently no source for strong electric fields. There is no requirement to make any further assessment of exposures in these situations Magnetic fields Strong magnetic fields may be generated in the vicinity of the static frequency converter cabinet during generator start-up and prior to firing the gas turbine. It is understood that the highest currents are provided during initial acceleration of the generator and so measurement results from a single start-up may not give an accurate indication of the spatial distribution of the fields. The measured fields did not exceed the low action levels, but did represent 570% of the Council Recommendation. Magnetic flux densities exceeded the up to 0.6 m from the surfaces of the cabinets. Spectral analysis of the fields indicated the presence of multiple frequency components. It was not possible to directly assess exposures during a live brush change on the generator exciter, so exposures were assessed by assessing whole body exposures around the brush gear enclosure and limb exposures in contact with the exciter cables. Exposures outside the 7

16 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK exciter brush gear enclosures, which is where whole body exposures would occur, were generally around 15 20% of the low action levels. Exposures in contact with the exciter cables, which approximate to the position of the hands during a live brush change, represented less than 2% of the limb action levels. As noted above, magnetic flux densities around the exciter brush gear were generally around the and in the worst case were 190% Control Measures In the absence of a person-specific individual assessment, employees at particular risk should be excluded from access to all parts of generator excitation systems whenever it is operational. Employees with active implanted medical devices and those using body-worn medical devices should be excluded from the area around the static frequency converter during start-up. As the strong fields are of very limited duration, there should be no need to restrict access by employees with passive implants or those who are pregnant Triggers for Reassessment These include any significant change to the design of static frequency converters or generator excitation systems. 5.3 Power Distribution Description of Activity The generator terminals normally feed power into an isolated phase bus. For each phase this consists of a hollow conductor of circular, octagonal, or hexagonal cross-section housed centrally within a non-magnetic metallic enclosure that is grounded. The flow of current through the conductor induces an opposing current flow in the enclosure that normally results in significant cancellation of magnetic fields. The isolated phase bus delivers power to the generator transformer, which steps up the voltage from the generator voltage (normally around kv) to the grid voltage (normally 275 or 400 kv). The output phases from the generator transformer normally pass to a banking compound or National Grid substation via overhead exposed busbars, overhead exposed lines, or underground insulated cables, or a combination of the above. There are normally tee junctions on the isolated phase bus to tap power off to the unit auxiliary transformer. This transformer provides power to run the unit and is normally tapped to provide 11 kv and 6.6 kv outputs, although for some stations the latter may be replaced with a 3.3 kv tap. The output from this transformer is distributed via high voltage switchgear in dedicated switch rooms and will be used to feed transformers stepping down to 415 V. The output from these transformers is distributed via low voltage switchgear. The transformers are cooled using a variety of approaches, including integral cooling fans of various sizes, separate cooling units incorporating integral cooling fans and separate cooling units utilising cooling water. 8

17 RISK ASSESSMENTS Summary of Exposures Electric fields There are overhead exposed busbars and lines maintained at high potential and it would therefore be expected that there will be strong electric fields. These fields did not exceed the low action levels in generally accessible areas of the power stations surveyed. However, localised electric field strengths inside the banking compounds may exceed the low action levels. There appeared to be local differences in access to the banking compounds, with staff at some stations reporting that they never entered these areas, whilst staff at other stations considered access to be a matter of routine. In some cases electric field strengths in the generator transformer compound and in localised areas outside the banking compound exceeded the Council Recommendation reference levels. In one particular case, the outgoing 400 kv conductors passed back across the power station site at relatively low level. This resulted in the being exceeded on a grassy area used for social events attended by staff and their families. If family members are not employees, the should apply Magnetic fields For the stations surveyed, magnetic fields in the vicinity of the isolated phase bus, where this was accessible, were below the low action levels, but in some cases exceeded the Council Recommendation by a considerable margin. Magnetic fields around the generator and unit auxiliary transformers were below the low action levels, but in some cases exceeded the Council Recommendation in localised areas, particularly in the vicinity of output cables from the latter. In addition, strong fields were often accessible in the vicinity of earth conductors and whilst these did not exceed the low action levels, they sometimes exceeded the by a considerable margin. Strong magnetic fields are generated in high voltage (11 kv) switch rooms. This is to be expected as the cables from the unit auxiliary transformers (carrying 100 s of amperes) enter these switch rooms. Magnetic flux densities may exceed the low action levels, but where this was observed, it was restricted to a region that was too localised to give rise to whole body exposures. The may be exceeded in these switch rooms. In addition, in one case an earth conductor from a high voltage switch room, but running outside it, was carrying sufficient current to generate a magnetic flux density that exceeded the. Accessible magnetic flux densities in medium voltage (6.6 kv) and low voltage (415 V) switch rooms were either below the low action levels, or exceeded them over a volume too small to give rise to whole body exposures. Exposures were generally below the, although in a small number of instances localised exposures could exceed them. Magnetic flux densities measured in 3.3 kv switch rooms were below the action and. However, it is recognised that this finding is based on a very small sample and by inference from data on 11 kv, 6.6 kv and 415 V switch rooms it appears likely that some 3.3 kv switch rooms may contain localised areas where the may be exceeded. At one station where the National Grid substation was fed by underground phase conductors from the generator transformer, magnetic flux densities exceeded the Council Recommendation at heights of up to 0.6 m above the top of the conductor 9

18 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK trench. For all other stations surveyed, magnetic flux densities outside banking compounds and National Grid substations did not exceed action levels or Assessment of Exposures Electric fields There are exposed high voltage conductors associated with generator transformer compounds and transmission of power to banking compounds and National Grid substations. These will result in the generation of strong electric fields. Nevertheless, the presence of earthed metal fencing around transformer and banking compounds, together with earthed metal transformer casings and other large earthed metallic structures will perturb the electric field. As transformer compounds typically occupy a relatively small area, the consequence of the field perturbation will be to reduce the electric field strength close to ground level. Hence, in general the electric field strengths measured inside transformer compounds were below both the low action levels and the Council Recommendation, although at Staythorpe electric field strengths in the generator transformer compound under relatively lowslung conductors were 110% of the. Electric field strengths outside transformer and banking compounds and beneath outgoing conductors were all below both the low action levels and the. In these cases conductors are often higher than in the transformer compounds and earthed metal fencing to a height of approximately 2 m will normally still be present Magnetic fields In general the isolated phase bus is inaccessible, but access is sometimes provided for the purposes of inspection or access to the main generator circuit breaker. Electric currents induced in the outer metal casing of the isolated phase bus will tend to generate magnetic fields that cancel those produced by current flow through the conductors. Where fields were assessed close to the bus, they did not exceed the low action levels, although they sometimes exceeded the Council Recommendation with the maximum measured value being 400% for a standard bus. Where inspection windows are present, field strengths may be even higher with a maximum measured value being 570% of the. Magnetic flux densities around generator and unit auxiliary transformers did not exceed the low action levels for any of the surveys. However, strong fields representing up to 700% of the were measured around generator transformers, although there was considerable variation from site to site, presumably reflecting the details of individual installations and accessibility of phase tanks. Magnetic fields around unit auxiliary transformers were generally lower, although where output cables were accessible, the fields around these could be up to 700% of the. Interestingly strong fields were also measured in the vicinity of the earth conductors connected to the transformers (and at Aberthaw an earth conductor from a high voltage switch room), which could also represent up to 700% of the. Strong magnetic fields have been measured in 11 kv switch rooms. At Drax magnetic flux densities exceeded the low action levels, but only over a very localised region that could not give rise to whole body exposures. Accessible fields around switch gear were around 100% of 10

19 RISK ASSESSMENTS the in a number of cases. Field strengths in 6.6 kv, 3.3 kv and 415 V switch rooms were generally much lower and did not exceed the action levels. Magnetic flux densities in localised areas within 11 kv, 6.6 kv and 415 V switch rooms exceeded the Council Recommendation. Similar strong fields were not identified in 3.3 kv switch rooms, but it is recognised that this finding is based on a very small sample and by inference from the fields measured in other switch rooms it appears likely that some will contain localised areas where the may be exceeded. Accessible magnetic flux densities around the boundaries of banking compounds, National Grid substations and outgoing conductors were generally well below the action and reference levels and were not hazardous. At both Aberthaw and Heysham 2, where the National Grid substations are fed from underground cables, magnetic flux densities above the conductor trenches were elevated. At Aberthaw the field strengths at the ground surface were at the, but this is not considered to be a normally accessible location. However, at Heysham 2 the magnetic flux densities exceeded the at up to 0.6 m above ground level Control Measures In the absence of a person-specific individual assessment, employees with active implants or body-worn medical devices should be excluded from access to the generator and unit auxiliary transformer compounds, and high voltage switch rooms during operation of the unit. As these are normally areas with restricted access, this should be straightforward. Consideration should also be given to whether restrictions are appropriate for those with passive implants or who are pregnant. An important consideration here will be the localised nature of the strong fields, which reduces the likelihood of someone spending a long time exposed to the strong field. Access to earth conductors carrying high currents and to the areas above phase conductor trenches will also need to be considered Triggers for Reassessment Unusual configuration resulting in abnormally large separation of phases, where they would normally be bundled together could lead to higher resultant fields. 5.4 Ancillary Equipment Description of Activity A wide range of motors are used to drive cooling water pumps, oil pumps, feed water pumps, cooling tower drives and booster fans. In addition, coal- and biomass-fired power stations normally have motors driving conveyors and vibratory feeders as part of their fuelling systems. They may also have equipment such as precipitators to removed fine particles from flue gasses, along with flue gas desulphurisation (FGD) systems. 11

20 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Summary of Exposures Electric fields There are no exposed high voltage conductors associated with any of the ancillary equipment and consequently no expectation of strong electric fields Magnetic fields None of the ancillary equipment is expected to generate magnetic flux densities that exceed the low action levels. Some pump and fan motors assessed generated magnetic fields that were strong enough to exceed the Council Recommendation in close proximity to the motor housings. In general magnetic flux densities fall rapidly with distance so that exposures fell below the within 0.3 m. These highly localised strong fields should not present a risk to most employees at particular risk. However, employees with active implants or body-worn medical devices who are required to work in close proximity to an operating motor could be at risk. The size or power of a motor is not a good predictor for the strength of the field generated. This is illustrated by the cooling water pump shown in Figure 2. The magnetic flux density at the surface of the main pump represented <1% of the low action levels and 1.3% of the. In contrast the field at the surface of the small motor for the auxiliary cooling water pump, which provides cooling water to cool the main pump, represented 590% of the. Main cooling water pump Figure 2 Main and auxiliary cooling water pumps at Didcot B Power Station Auxiliary cooling water pump 12

21 RISK ASSESSMENTS Assessment of Exposures Electric fields There are no exposed high voltage conductors in these areas and consequently no source for strong electric fields. There is no requirement to make any further assessment of exposures in these situations Magnetic fields Accessible magnetic fields measured around high power motors such as those driving cooling water pumps were variable, with the lowest representing around 1% and the highest 370% of the Council Recommendation. This range probably reflects a number of factors including the age of the motors (modern motors will often be more efficient) the thickness of the pump housing and the presence or absence of acoustic insulation. In general field strengths fell rapidly with distance and the fields would be unlikely to result in whole body exposures. Large fan motors were also variable, with some generating strong fields in close proximity to the motor, but again these would be unlikely to result in whole body exposures in excess of either the low action levels or the. Accessible magnetic flux densities were often higher for smaller lower power motors, such as those driving feed water pumps, oil pumps, and ventilation fans, where exposures could exceed the close to the motors. Perhaps the best example of the difference between large and small motors was the cooling water pump at Didcot B. Here the magnetic flux density at the surface of the motor for the main cooling water pump was around 1% of the, but the field generated by the motor of the auxiliary pump delivering coolant to the main pump was 590% of the. In general, fields from small motors fall rapidly with distance, so that they should not result in hazardous exposures for employees at particular risk who are working in the general area. However, there may be risks for employees with active implanted medical devices if they are required to work very close to one of these small motors whilst it is operating. Similarly motors associated with conveyors and vibratory feeders were also variable, but those assessed were generally below the action and. Strong fields were also generated around precipitator supply and control equipment, particularly the rectifiers. However, the strongest assessed field represented just 3% of the low action levels and 74% of the and was not hazardous Control Measures There is no need for general restriction on access to areas housing ancillary equipment. In the absence of a person-specific individual assessment, employees with active implants or body-worn medical devices should not be required to work in close proximity to operational motors Triggers for Reassessment More efficient motor designs may result in reduced field generation. 13

22 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK 6 DISCUSSION The Control of Electromagnetic Fields at Work Regulations 2016, which implement the EMF Directive (2013/35/EU), came into force on 1 st July These regulations introduced requirements for employers to assess exposures and, where appropriate, risks arising from work that generates strong electromagnetic fields. Employers will need to consider whether exposures could exceed the action levels specified in the new legislation. The action levels are not themselves limits, but are derived from exposure limit values that are mostly set in terms of internal quantities within the body, which cannot be easily measured. Hence if the action levels are exceeded employers will need to decide whether to pursue a more detailed assessment in order to demonstrate compliance, or simply restrict exposure. In many cases, the latter option will be more cost-effective. Employers will also need to consider employees at particular risk (defined in guidance as including those with active implanted medical devices, those with passive implanted medical devices, those with body-worn medical devices and pregnant women). Employees at particular risk may not be adequately protected by the action levels specified in the new legislation. In general these employees will be adequately protected by compliance with the specified in Council Recommendation 1999/519/EC. In many cases it would probably be safe to exceed these, but for various reasons it may be difficult to demonstrate this. A pragmatic first approach for most employers will be to identify any areas where exposures may exceed either the action levels specified in the new legislation or the specified in Council Recommendation 1999/519/EC. This will permit a considered approach to managing the risks associated with such exposures. In the case of employees at particular risk, there would be a choice to either restrict access to these areas or alternatively to look at a specific assessment, which will be dependent on the individual situation. Whilst access restrictions will often be the default approach, most employers will want to keep open an option to permit access to specific individuals where it can be shown that this will not put them at unnecessary risk. In relation to access restrictions it is relevant to consider the nature of the risk. Those with active implants or body-worn medical devices are at risk of device malfunction during even transient exposure. Hence these individuals should not enter any area where whole body exposures in excess of the are possible unless it can be shown that the particular device on which they rely is not susceptible to interference at the field strengths present in that area. Localised strong fields may also present a risk if it is foreseeable that they could give rise to exposure of the device. Hence these employees should also keep away from equipment capable of generating localised strong fields. The situation for those with passive implants and pregnant women is somewhat different. Passive implants may result in localised field enhancements within the surrounding tissues, but in the absence of sharp points on the implant these are unlikely to be large. Implants may also be subject to inductive heating, the magnitude of which will depend on a number of factors. However, even if inductive heating is likely to be significant, it will take time for the temperature of the surrounding tissue to rise so that simply passing through an area is unlikely 14

23 DISCUSSION to result in harm. Similarly for pregnant women, any adverse effect on the fetus would require prolonged exposure and passing through an area is unlikely to result in harm. In order to assist its members operating power generation plant, Energy UK commissioned Public Health England s Centre for Radiation, Chemical and Environmental Hazards to carry out a survey of potential exposures at a sample of six power stations. The results of this assessment should enable operators to identify areas where access restrictions may need to be implemented. 6.1 Exposures in Excess of the Action Levels There were only three situations where fields could give rise to whole body exposures equal to or exceeding the action levels specified in the new legislation. Two of these related to magnetic fields and one to electric fields. Field strengths in excess of the low action levels were measured in a small number of other situations, but were restricted to volumes too small to result in whole body exposures. One area where magnetic fields were exceeded was a small region surrounding generator exciter cables running up the outside of the enclosure for a generator exciter transformer. The region was just large enough to result in whole body exposures. The second situation was a small region around the generator neutral point beneath a generator. Again the region was just large enough to result in whole body exposures. In both situations, magnetic flux densities equalled or exceeded both the low and high action levels. As exposures could exceed the high action levels it will be necessary for operators to restrict access to these areas whilst the equipment is operating. For the specific examples surveyed the size of the restricted access areas would be 0.4 m for the excitation cables and 0.6 m for the neutral point conductors. To avoid the necessity for surveying similar situations at other stations, doubling these distances should be sufficient to allow for site to site variability. Access restriction would be most effectively achieved by means of physical barriers, but suitable floor markings could be considered as an alternative. The electric field low action levels were exceeded inside a banking compound at Connah s Quay Power Station. The practice with respect to station staff going into banking compounds appeared to vary from station to station, with staff at some stations saying that they routinely enter the banking compound, whilst staff at other stations claimed to rarely or never enter these areas. The main risk in areas where the low action levels for electric field strength are exceeded is one of spark discharges. Actions to mitigate these risks could include provision of suitable training, implementation of technical measures and use of personal protective equipment. Some or all of these measures may already be in place. 6.2 Exposures in Excess of the Reference Levels As might be expected there were far more examples of situations where the may be exceeded. In some situations, such as transformer compounds and high voltage switch rooms, the strong fields were localised and present in areas that have restricted access anyway. The strong fields generated around static converter cabinets during start-up of gas turbines are generally present for only a few minutes and these cabinets may well be located in areas with restricted access such as switch rooms. In other situations, such as around 15

24 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK generators, generator exciter systems and accessible parts of isolated phase busses, it may be necessary to consider imposing additional access restrictions. These restrictions would also apply during activities such as live brush changing, which necessarily bring the personnel involved into close proximity with the generator excitation system. In some areas, such as beneath outgoing conductors effective restriction of access may be more difficult to achieve. These are good examples of situations where there would be no need to prevent those with passive implants or pregnant women from passing through the area. In contrast, those fitted with active implants or using body-worn medical devices would need to stay out of the area unless it could be shown that the device on which they rely was unaffected by the field. Magnetic flux densities in excess of the were also generated around a variety of motors of different sizes and powers. In general these strong fields were highly localised and dropped below the within 0.3 m. Hence they should not constitute a risk for most employees at particular risk. However, in the absence of a person-specific individual assessment, employees with active implanted medical devices or body-worn medical devices should not be required to work in close proximity to operating motors. 16

25 APPENDIX A APPENDIX A Legislation and Guidance A1 Control of Electromagnetic Fields at Work Regulations 2016 The Control of Electromagnetic Fields at Work Regulations 2016 came into force in July This legislation is broadly consistent with the requirements of existing legislation, particularly the Management of Health and Safety at Work Regulations 1999, but is more specific in a number of areas. A1.1 Exposure Limit Values and Action Levels The Regulations define exposure limit values and associated action levels. These are similar in principle to the basic restrictions and specified in the ICNIRP 1998 guidance, but with some important differences. Importantly, the basic restrictions advised by ICNIRP are guidelines, whereas the exposure limit values specified in the legislation are legally enforceable limits. There are other differences as well: the legislation brings together limits for both static magnetic and time varying electromagnetic fields, which are covered in separate ICNIRP guidance documents the system of exposure limit values is more complex than the system of basic restrictions with separate limits for sensory and health effects reflecting the more complex system of exposure limit values, the system of action levels is also more complicated with low, high and, in some cases, limb action levels at low frequencies the breakpoint for protection against surface heating is reduced from 10 GHz to 6 GHz action levels for radiofrequency power density are only specified for frequencies above 6 GHz; below this frequency action levels are only specified in terms of electric and magnetic field strength Exposure limit values and action levels are discussed in more detail in section A3 below. A1.2 Exposure Assessment The Regulations require all employers to make a suitable and sufficient assessment of potential exposure of employees to electromagnetic fields. However, there is no requirement for this assessment to be made by means of calculation or measurement unless this is the only way to demonstrate compliance. Other information that may be taken into account includes: emission and other safety-related data provided by the manufacturer of distributor of equipment used by the employer industry standards and guidelines the European Commission s practical guide guidance produced by HSE 17

26 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Employers must keep a record of the significant findings from the most recent exposure assessment. A1.3 Risk Assessment The Regulations introduce requirements for employers to assess risks arising from work with electromagnetic fields and radiations at frequencies between 0 and 300 GHz. These electromagnetic fields-specific risk assessments are not necessary where: the most recent exposure assessment shows that exposures are compliant with the exposure limit values the indirect effects action levels are not exceeded there are no employees at particular risk In carrying out an electromagnetic fields-specific risk assessment, the employer is required to consider both indirect effects and employees at particular risk. Indirect effects are those caused by the presence of an object or substance in the field and include: interference with medical electronic equipment projectile risk from strong static magnetic fields initiation of electro-explosive devices fires and explosions resulting from ignition of flammable materials by sparks caused by induced fields, contact currents, or spark discharges contact currents. Employees at particular risk are defined as: those employees who have declared to their employer a condition that may lead to a higher susceptibility to the potential effects of exposure to electromagnetic fields an employee who works in close proximity to electro-explosive devices, explosive materials, or flammable atmospheres Both the Directive itself and the HSE guidance to the Regulations identify several groups of employees who are likely to have a higher susceptibility to the potential effects of exposure to electromagnetic fields. These are: those fitted with active medical implants (such as cardiac pacemakers, cardiac defibrillators, and neurostimulators) those fitted with passive medical implants (essentially any metallic implant including a variety of artificial joints, pins, plates, screws and contraceptive implants) those wearing body-worn medical devices (such as insulin infusion pumps) pregnant women By definition, employees at particular risk may not be adequately protected by the action levels or exposure limit values. In general, these employees will be adequately protected by the specified in Council Recommendation 1999/519/EC. In some cases it may be possible to exceed these without risk, but this would generally have to be determined on a case by case basis and may be difficult to demonstrate Where relevant, an electromagnetic fields-specific risk assessment must include consideration of: 18

27 APPENDIX A the action levels and exposure limit values the frequency, level, duration and type of exposure, including the distribution over the employee s body and the variations between areas in the workplace direct biophysical effects existence of replacement equipment designed to reduce the level of exposure to electromagnetic fields appropriate information obtained from health surveillances information provided by the manufacturer of relevant equipment other health and safety related information multiple sources of exposure simultaneous exposure to multiple frequency fields Where an electromagnetic fields-specific risk assessment is required, the employer must keep a written record of the most recent assessment. A1.4 Action Plan Employers are required to draw up and implement an action plan to achieve compliance with the exposure limit values, unless either: exposures are already compliant; or the work activity is exempt from compliance. Where relevant, the action plan should include consideration of: alternative working methods involving lower exposure replacement equipment producing lower exposures technical measures to reduce emissions of electromagnetic fields, including interlocks, screening or similar protection measures demarcation and access control maintenance programmes for equipment, workstations and workplaces design and layout of workstations and workplaces limitations on the duration and intensity of exposure availability of suitable personal protective equipment The purpose of the action plan is to achieve compliance with the exposure limit values, so whenever there is evidence that the exposure limit values have been exceeded, employers are required to identify and implement whatever changes are needed to reduce exposures below the exposure limit values. Where an action plan is required, the employer must keep a written record of the most recent plan. 19

28 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK A1.5 Avoiding or Reducing Risks The Regulations require that having completed the risk assessment, employers should implement measures to either eliminate risks or reduce them to a minimum. The approach taken should follow the principles established by the Management of Health and Safety at Work Regulations In particular, employers are required to consider: technical progress potential to restrict access to parts of the workplace availability of measures to control the production of electromagnetic fields at source A1.6 Employee Information and Training The Regulations require employers to provide employees who may be exposed to risks from electromagnetic fields and radiations to be given appropriate information and training. A2 Exposure Limit Values and Action Levels A2.1 Sensory and Health Effects Exposure Limit Values The Control of Electromagnetic Fields at Work Regulations 2016 define separate exposure limit values for sensory and health effects (Figure A1). The sensory effects exposure limit values only apply to specific frequency ranges (0 400 Hz and GHz). For low frequencies (non-thermal effects), perception of the field occurs at exposure levels lower than those producing health effects. The radiofrequency (thermal) sensory effects exposure limit value is based on the avoidance of the microwave hearing effect, which only occurs under specific conditions. In contrast, health effects exposure limit values apply to all frequencies. In general, it is permissible to temporarily exceed the sensory effects exposure limit values for short periods providing certain conditions are met. A2.1.1 Exposure limit values for frequencies up to 1 Hz Exposure limit values for the frequency range of 0 1 Hz are defined in terms of external magnetic flux density (Table ELV1 of Part 2 of the Schedule). The sensory effects exposure limit values are set to prevent vertigo and other perceptual effects. These mainly result from electric fields induced in tissues when the body moves in a strong static magnetic field, although there is now some evidence that they can occur in the absence of movement. Hence for a controlled working environment where movement in the field is limited and employees are provided with information, it may be permissible to temporarily exceed the sensory effects exposure limit values provided this is justified by the practice or process. In this case exposures must not exceed the health effects exposure limit value. A2.1.2 Exposure limit values for low frequency fields The exposure limit values in the frequency range of 1 Hz 10 MHz are defined in terms of internal electric fields induced in the body (Table ELV2 and Table ELV3 of Part 2 to the Schedule). 20

29 APPENDIX A For frequencies up to 400 Hz, there are both sensory effects exposure limit values and health effects exposure limit values. The sensory effects exposure limit values are intended to prevent retinal phosphenes and minor transient changes in brain function. Consequently they only apply to the central nervous system (cns) tissues within the head of the exposed employee. The health effects exposure limit values apply to all frequencies between 1 Hz and 10 MHz and are intended to prevent stimulation of peripheral and central nerves. Hence these exposure limit values apply to all tissues throughout the body of an exposed employee. Figure A1 Range of frequencies over which different ELVs are used. Blue bars indicate non-thermal effects and red bars thermal effects A2.1.3 Exposure limit values for radiofrequency fields For frequencies in the range 100 khz 6 GHz, the degree of heating resulting from exposure depends on the rate at which energy is absorbed in tissues. This is defined by the specific energy absorption rate (SAR), which is used to specify the health effects exposure limit values, with separate values for whole body and localised exposures (Table ELV4 of Part 2 of the Schedule). The whole body values protect from heat stress and heat stroke and are applied to the SAR averaged over the entire body. The localised values protect from thermal injury to specific tissues and are applied to the SAR averaged over any 10 g of contiguous (or connected) tissue. Both whole body and localised SAR are averaged over a 6 minute period. For frequencies in the range 300 MHz 6 GHz there are also sensory effects ELVs that are intended to prevent the microwave hearing phenomena resulting from exposure to pulsed 21

30 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK fields (Table ELV5 of Part 2 of the Schedule). These are specified in terms of specific absorption (SA) averaged over 10 g in the head. Penetration of electromagnetic energy into the body decreases with frequency in the radiofrequency range, so that for frequencies above 6 GHz the field is absorbed mostly on the surface of the body. This means that for these frequencies it is much more relevant to limit power density incident on the body surface than the rate at which energy is absorbed into a mass of tissue. The power density is averaged over 20 cm 2, subject to a limit on the maximum averaged over any 1 cm 2. For frequencies in the range 6 10 GHz the power density is averaged over any 6 minute period. Beyond this the averaging time decreases with increasing frequency reflecting decreasing penetration depth (Table ELV6 of Part 2 of the Schedule). A2.2 Action Levels The exposure limit values for time varying fields with frequencies between 1 Hz and 6 GHz are set in terms of internal body quantities that are not easily measurable in people, and the Electromagnetic Fields Directive therefore specifies action levels of external electric and magnetic field strength that may be compared directly with measured or calculated exposure levels. The action levels have been derived from the exposure limit values using dosimetric models that assume conservative exposure conditions, such as the electric field strength being uniform over the space occupied by an exposed person. This is illustrated in Figure A2. Increasing risk Level, duration and type of exposure Prevention measures required Assessment against ELVs required Temporary exposure only Awareness training / information required Limit spark discharges for E-fields Assessment for workers at particular risk required Increased health and safety risks Sensory field effects (eg phosphenes, microshocks) Council Recommendation Health ELV High AL Sensory ELV Low AL Figure A2 Schematic showing relationship between exposure limit values and action levels 22

31 APPENDIX A Comparison of measurements with the action levels can be used to demonstrate compliance with the exposure limit values. However, action levels are not limits and if they are exceeded it does not necessarily follow that the exposure limit values are exceeded. The action levels are frequency dependent and are illustrated in Figures A3 A6. The action levels are most restrictive over the frequency range MHz where electromagnetic energy couples most efficiently into the body. All of the action levels are specified as root mean square (rms) values. A2.2.1 Action levels for low frequency electric fields For frequencies between 1 Hz and 10 MHz, the Control of Electromagnetic Fields at Work Regulations 2016 define two action levels for electric fields, low and high (Figure A3). The concept of low and high ALs is illustrated in Figure A2. Compliance with the low action level will ensure that neither of the applicable exposure limit values will be exceeded and will also prevent annoying spark discharges in the work environment. Figure A3 Low frequency action levels for electric field strength. The high action level is shown in red, the low action level is shown in yellow and the Council Recommendation reference level is shown in green If electric field strengths exceed the low action level, compliance with the high action level will not, on its own, be sufficient to prevent annoying spark discharges. Hence in this situation it is necessary to implement additional technical, organisational and, if appropriate, personal protective measures to limit spark discharges. 23

32 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK A2.2.2 Action levels for low frequency magnetic fields For frequencies between 1 Hz and 10 MHz, there are three action levels for magnetic flux density: low, high and limb (Figure A4). The low action levels are derived from the sensory effects exposure limit values such that compliance guarantees compliance with both sensory effects and health effects exposure limit values. Low action levels have the same value as high action levels for frequencies above 300 Hz. Compliance with the high action levels will guarantee compliance with the health effects exposure limit values, from which they are derived, but will not ensure compliance with the sensory effects exposure limit values at frequencies below 300 Hz. The low action levels may be exceeded, provided it can be shown either that the sensory effects ELVs are not exceeded, or if they are exceeded, that this occurs only temporarily. Nevertheless, the health effects exposure limit values must not be exceeded. Moreover, employees must be informed about possible transient symptoms and sensations. Where transient symptoms are reported the employer is required, if necessary, take action to update the risk assessment and prevention measures. Figure A4 Low frequency action levels for magnetic flux density. The high action level is shown in red, the low action level is shown in yellow, the limb action level is shown in orange and the Council Recommendation reference level is shown in green. Compliance with the limb action levels will ensure compliance with the health effects exposure limit values, from which they are derived. The limb action levels take account of weaker coupling of the field into the limbs and are consequently less restrictive than the high action levels. Use of the limb action levels would only be justified where body exposure at the same 24

33 APPENDIX A field strength is unlikely. So their use would be justified in the case of an employee holding a tool generating electromagnetic fields, but not if the tool was being held next to the body when in use. Where assessment of limb exposure against the limb action level is carried out, it would be normal practice to also assess body exposure against the low or high action level as appropriate. A2.2.3 Electric and magnetic field action levels for frequencies between 100 khz and 6 GHz For frequencies between 100 khz and 6 GHz, the Control of Electromagnetic Fields at Work Regulations 2016 define action levels for electric field strength and magnetic flux density, which are derived from the health effects exposure limit values. As the underlying exposure limit values are time averaged values, the square of the action level should be averaged over any six-minute period. Figure A3 High frequency action level for electric field strength (red line). The Council Recommendation reference level is shown in green. A2.2.4 Action levels for frequencies between 6 GHz and 300 GHz For frequencies above 6 GHz, the Control of Electromagnetic Fields at Work Regulations 2016 define action levels for electric field strength, magnetic flux density and radiofrequency power density. The power density action level should be averaged over any 20 cm 2 of exposed area, subject to the condition that spatial maximum averaged of any 1 cm 2 should not 25

34 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK exceed 20 times the action level (S). Power density action levels are also time averaged, over any six-minute period for frequencies up to 10 GHz, and over any 68 /f1.05 minute period for higher frequencies (where f is the frequency in GHz). Beyond this the averaging time decreases with increasing frequency reflecting decreasing penetration depth. For frequencies above 6 GHz, the action levels for electric field strength and magnetic flux density are derived from the power density exposure limit value. Hence, although not explicitly stated in the Control of Electromagnetic Fields at Work Regulations 2016, for consistency the spatial and time averaging conditions for action level (S) should also apply to [action level (E)] 2 and [action level (B)] 2 at frequencies above 6 GHz. Figure A4 High frequency action level for magnetic flux density (red line). The Council Recommendation reference level is shown in green. A3 Exemption Certificates Regulation 13 of the Control of Electromagnetic Fields at Work Regulations 2016 grants the Health and Safety Executive the power to exempt employers from the requirements of Regulations 4(1) (exposure limit values) and 7 (action plan). Such exemptions may only be granted provided exposures to electromagnetic fields are as low as reasonably practicable and employees are protected against health and safety risks related to exposure. To date only one exemption certificate has been issued. This exempts a range of work activities: electrolysis as part of a manufacturing process 26

35 APPENDIX A use of dielectric heating equipment use of induction heating equipment use of manually-operated resistance welding equipment use of magnetic resonance imaging equipment other than for patients in the health sector This exemption certificate clearly applies in the case of induction heating within the School of Metallurgy and Materials. A4 Practical Guide The Directive from which the Control of Electromagnetic Fields at Work Regulations 2016 are derived placed an obligation on the European Commission to publish a practical guide to its implementation. This was prepared by Public Health England on behalf of the Commission and was published at the end of A5 Council Recommendation 1999/519/EC Although employees at particular risk may not be adequately protected by the action levels specified in the Control of Electromagnetic Fields at Work Regulations 2016, they will not normally be at risk provided exposures do not exceed the specified in Council Recommendation 1999/519/EC. This Recommendation provides a framework to protect members of the general public from the established adverse health effects that may result from exposure to electromagnetic fields. The Council Recommendation is non-binding, but sets out a system of basic restrictions, which are quantities that should not be exceeded and are conceptually equivalent to the ELVs used in the Control of Electromagnetic Fields at Work Regulations As the basic restrictions are mostly set in terms of internal quantities within the body that cannot be readily measured, the Council Recommendation also sets out a system of set in terms of external field quantities that can be more readily assessed (illustrated in figures A3 A6). The are derived from the basic restrictions using conservative approaches such that provided the are not exceeded, then the underlying basic restrictions will not be exceeded. However, as the derivation of the is based on worst case assumptions, it is often possible to exceed the and still not exceed the basic restrictions. In this respect the are conceptually equivalent to the action levels used in the Control of Electromagnetic Fields at Work Regulations The system of protection described in the Council Recommendation has been widely adopted as a framework for protection of the general public. In particular, the specified in the Council Recommendation have been used as a basis for managing exposures in many publicly accessible areas. In addition, the have been used to inform the development of standards for the electromagnetic immunity of active implanted medical devices. 27

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37 APPENDIX B APPENDIX B Measurement Equipment and Survey Methods B1 Low Frequency Magnetic Fields Measurements of magnetic flux density were made using either a Narda ELT-400 exposure level meter or a Narda EFA-300 FFT Electromagnetic Field Analyser. B1.1 ELT-400 The ELT-400 (serial numbers: N-0422 [Aberthaw and Didcot B] and N-0423 [Connah s Quay, Drax, Heysham 2 and Staythorpe]) is a rugged magnetic field meter specified for frequencies between 1 Hz and 400 khz. It is used in conjunction with either an isotropic 100 cm 2 precision probe (serial numbers: M-0862 [Aberthaw and Didcot B] and M-0863 [Connah s Quay, Drax, Heysham 2 and Staythorpe]) or an isotropic 3 cm 2 probe (serial numbers: C-0146 [Aberthaw and Didcot B] and C-0147 [Connah s Quay, Drax, Heysham 2 and Staythorpe]). Unless otherwise stated measurements were made using the 100 cm 2 probe. The meter incorporates a series of shaped time domain filters that are applied directly to the measured signal in order to account for the shape of the action levels. These filters effectively account for the contribution of different frequencies by applying the weighted peak method in the time domain as specified in the EMF Directive. This approach allows for phase and results are displayed directly as a percentage of the relevant action levels. The ELT-400 meter is equipped with both root mean square (rms) and peak detectors. B1.2 EFA-300 FFT This instrument consists of an intelligent meter (serial numbers: K-0047 [Aberthaw and Didcot B] and O-0021 [Connah s Quay, Drax, Heysham 2 and Staythorpe]) with a digital display used with an external isotropic 100 cm 2 precision magnetic field probe (serial numbers: AB-0004 [Aberthaw and Didcot B] and AG-0015 [Connah s Quay, Drax, Heysham 2 and Staythorpe]). The unit is specified for frequencies between 5 Hz and 32 khz. The EFA-300 FFT incorporates a fast Fourier transform mode that allows live spectra to be recorded whilst the test equipment is energised. This was used to make spectral measurements. The EFA-300 FFT also incorporates a shaped time domain mode that applies the weighted peak approach in the time domain and thus forgoes splitting the signal into its various frequency components for comparison with corresponding. The influence of frequency is taken into account using shaped-frequency-response filters, and the approach also allows for phase. The measurement result is displayed as a percentage of the Council Recommendation. B2 Low Frequency Electric Fields Measurements of electric field strength were again made using the Narda Electromagnetic Field Analyser type EFA-300 FFT (serial numbers: K-0047 [Aberthaw and Didcot B] and 29

38 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK O-0021 [Connah s Quay, Drax, Heysham 2 and Staythorpe]) described in Section B1.2, but this time used with a Narda isotropic electric field probe (serial numbers: H-0032 [Aberthaw and Didcot B] and M-0005 [Connah s Quay, Drax, Heysham 2 and Staythorpe]) specified for frequencies between 5 Hz and 32 khz. The electric field probe was connected via a fibre optic link to the EFA-300 meter. B3 Static Magnetic Field Measurements of static magnetic flux density were made using a Metrolab three-axis hall magnetometer (model THM1176) [Drax]. This comprised a Socket SoMo 650 handheld computer loaded with Metrolab software used with a low field hall probe (serial number 0378) suitable for fields up to 8 mt. Measurements were made of the three-axis resultant static magnetic flux density using the low field probe. Each time the instrument was switched on at a new measurement location the reading was zeroed by inserting the probe into the zero gauss chamber. 30

39 APPENDIX C APPENDIX C Measurement Results Aberthaw Power Station During the survey the Unit 9 generator was operated at maximum capacity of 535 MW. The results of measurements of maximum magnetic flux densities and electric field strengths (as percentages of the low action levels and Council Recommendation ) are presented in the tables below. Results greater than or equal to 100% of the relevant level are presented in red font, those between 50% and 100% are presented in amber font. C1 Routine Generation Magnetic flux densities were surveyed around the Unit 9 generator, its pilot exciter, exciter and rectifier cabinets, and in accessible areas around the generator terminals. Results of the magnetic flux density survey are presented in Table C1 below. The spectral content of the magnetic fields was assessed near the pilot exciter and at the closest accessible point to the generator terminals (Figures C1 and C2 respectively). It can be seen that the pilot exciter has harmonic components at both 50 and 100 Hz, whereas the field around the generator terminals is dominated by the fundamental frequency of 50 Hz. Table C1 Maximum magnetic flux densities measured in the vicinity of the Unit 9 generator expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Generator stator sides 5 71 Non-drive end of generator stator Unit 9 pilot exciter 3* 40 At railings around pilot exciter 3 18 Unit 9 Exciter Unit 9 rectifiers back Unit 9 rectifiers -front Below generator at access door to generator terminals # * 3% of limb action levels in closest hand accessible areas at surface of pilot exciter 4% of limb action levels in closest hand accessible areas at surface of exciter Exceeds 100% of Council Recommendation across whole width of walkway alongside exciter Exceeds 100% of Council Recommendation across whole width of walkway at back of rectifiers # Falling to 100% of Council recommendation at top of stairs (approximately 2 m from door) 31

40 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Figure C1 Spectral content of magnetic fields around pilot exciter Figure C2 Spectral content of magnetic fields at entrance door to generator terminals 32

41 APPENDIX C C2 Power Distribution C2.1 Isolated Phase Bus The isolated phase bus was generally inaccessible. However, it passed close to the access walkway running along one side of the generator hall. Magnetic flux densities measured at the closest point of access represented 4% of the low action levels and 51% of the Council Recommendation. C2.2 Generator Transformer The Unit 9 generator transformer steps up the 22 kv output of the generator to 275 kv for transmission to the National Grid substation. Both electric and magnetic fields were surveyed in the generator transformer compound around the transformer and associated cabling and pylons. At Aberthaw the generator transformer has a water cooling system, with circulating oil used to transfer heat from the transformer to the cooling water system housed in an adjacent room. The fields generated by the cooling oil pump were also assessed. Results of the electric field survey are presented in Table C2 and the magnetic flux density survey in Table C3, below. A schematic drawing of the generator transformer compound, showing the approximate extent of the areas where the Council Recommendation reference levels are exceeded is given in Figure C3. The spectral content of the electric and magnetic fields in the generator transformer compound are presented in Figure C4 and Figure C5 below. It can be seen from these figures that the spectra are dominated by the fundamental frequency of 50 Hz. Table C2: Maximum electric field strengths measured in Unit 9 generator transformer compound expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation In Unit 9 generator transformer compound 2 3 Table C3 Maximum magnetic flux densities measured in Unit 9 generator transformer compound expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Side of transformer (away from overhead busbars) 34 >100* Side (beneath overhead busbars

42 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table C3 Maximum magnetic flux densities measured in Unit 9 generator transformer compound expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Area beneath overhead busbars around pylons - >100* Front at 0.5 m 8 - Around earth cable Around cables at base of pylons 35 >100* Maximum outside transformer compound - 43 Cooling oil pump 4 38 * Exposure exceeds 100% of throughout stated area Up to 10% of limb action levels close to earth Up to 13% of limb action levels at 0.1 m around cables Figure C3 Plan of generator transformer compound showing extent of areas where Council Recommendation are exceeded 34

43 APPENDIX C Figure C4 Spectrum of electric field measured beneath pylons in generator transformer compound Figure C5 Spectrum of magnetic fields measured in generator transformer compound C2.3 Unit 9 Auxiliary Transformer The Auxiliary transformer steps the 22 kv output from the generator down to 11 kv for distribution within the unit. Electric and magnetic fields were surveyed in the unit auxiliary 35

44 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK transformer room: around the transformer and associated cabling, earth connections and liquid oscillating resistor; and in accessible areas outside the room around the cooling system. Results of the magnetic flux density survey are presented in Table C4 below. A plan of the Unit 9 transformer room, showing the approximate extent of the areas where the Council Recommendation are exceeded is given in Figure C6. The spectral content of the magnetic field was measured around the Unit 9 transformer and is presented in Figure C7 below. It can be seen from this figure that the spectrum is dominated by the fundamental frequency of 50 Hz. Table C4 Maximum magnetic flux densities measured in the Unit 9 Auxiliary Transformer Building expressed as percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Around transformer Cables up side of transformer 41* 450 Cables in corner of transformer compound Earth connection Liquid oscillating resistor 4 51 * Up to 10% of limb action levels around cables Up to 12% of limb action levels around cables 36

45 APPENDIX C Figure C6 Plan of Unit 9 auxiliary transformer compound, showing extent of areas where the Council Recommendation are exceeded Figure C7 Spectral content of magnetic fields around Unit 9 auxiliary transformer 37

46 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK C2.4 Station Transformer No. 4 (132 kv - 11 kv) Magnetic fields were surveyed around station transformer No. 4, which steps down 132 kv to 11 kv. Associated cooling fans, conductors and control panel were also surveyed. Measurements were also made in accessible areas outside the transformer compound fence. The results of measurements are presented in Table C5 below. A measurement of the spectral content of the magnetic fields associated with the station transformer No. 4 was made; results are presented in Figure C8 below. It can be seen from this figure that the spectra are dominated by the fundamental frequency of 50 Hz. Table C5 Maximum magnetic flux densities measured around station transformer No. 4 expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Side of transformer * End of transformer Cooling fans 1 13 Around outward conductors Cooling control panel - 8 Max outside transformer compound fence - 7 * Falling to 100% at 2 m Falling to 100% at 0.1 m 38

47 APPENDIX C Figure C8 Spectral content of magnetic fields associated with station transformer No. 4 C2.5 Turbine House No.2 Transformer Magnetic fields were surveyed around the 3.3 kv 415 V Turbine House No. 2 Transformer, and in accessible areas around the outside of the transformer compound. The results of measurements are presented in Table C6 below. Table C6 Maximum magnetic flux densities measured around station Turbine House No. 2 Transformer, expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Around transformer 3 35 Max around outside of transformer compound - 4 C2.6 Flue Gas Desulphurisation (FGD) CW 11 kv Switch Room Magnetic fields were surveyed around switch gear in the FGD CW 11 kv switch room and around associated incoming cabling. The results of measurements are presented in Table C7 below. 39

48 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK A measurement of the spectral content of the magnetic fields associated with the switchgear was made; results are presented in Figure C9 below. It can be seen from this figure that the spectra are dominated by the fundamental frequency of 50 Hz, with minor contributions from harmonics. Table C7 Maximum magnetic flux densities measured in FGD Cooling Water 11kV switch room, expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Front of switch gear cabinets 1 6 Rear of switchgear cabinets 7* 100* Cables below station board incomer * Maximum by station board incomer Figure C9 Spectral content of magnetic fields associated with 11kV switchgear in FGD CW switch room C2.7 National Grid 275 kv Substation Building Magnetic and electric fields were surveyed in accessible areas around the outside of the National Grid Substation Building and beneath overhead power lines in the site car park. 40

49 APPENDIX C The results of the magnetic flux density survey around the Substation Building are presented in Table C8 below. Measurements of electric field strengths were also made in accessible areas outside the fenced compound containing connectors to pylons, and underneath power lines in the car park. Results are presented in Table C9. A measurement of the spectral content of the electric fields outside the substation was also made; the results can be seen in Figure C10. It can be seen that the spectrum is dominated by the fundamental frequency of 50 Hz. Table C8 Maximum magnetic flux densities measured around National Grid 275 kv Substation Building expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation No. 7 substation outside access doors 3 35 Cable entry point to no. 7 substation - 45 Cable entry point to No 8 substation (ground level) Cable entry point to No 8 substation (body level) Outside fenced compound to rear of substation, beneath connections to pylons Table C9 Maximum electric field strengths measured around National Grid substation expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Car park, beneath power lines to pylons Outside substation, beneath connections to pylons

50 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Figure C10 Spectral content of electric fields beneath connections to National Grid from substation C3 Ancillary Equipment C3.1 Precipitator Magnetic fields were surveyed around the transformer, supply boards and rectifiers associated with the precipitator. The results of measurements are presented in Table C10 below. Table C10 Maximum magnetic flux densities measured around precipitator transformer, rectifiers and supply boards, expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Precipitator heating and sapping gear supply board Supply board 2 19 Rectifiers - 17 Transformer rectifier 9C4 (415 V - 6 kv DC) Around outside of cage

51 APPENDIX C C3.2 Electric Motors A variety of electric motors of various sizes are used to drive pumps and fans throughout the station. Magnetic fields were surveyed around examples of motors used on the site. The results of measurements are presented in Table C11 below. Table C11 Maximum magnetic flux densities measured around various pumps, motors and fans, expressed as percentages of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation ID Fan 3.3 kv Motor Surface of motor 1 35 By cables 3 7 Walkway 1 5 Unit 9 FGD Booster Fan Motor (Hyundai 7430kW, 11 kv, 460A) Terminal box 8 86 Surface of motor 2 25 Cooling water pump motors (11 kv, 4 MW) No. 7 Cooling water pump * No. 9 Cooling water pump motor - around pump No. 9 Cooling water pump motor -at terminal box No. 10 Cooling water pump motor - around pump No. 10 Cooling water pump motor -at terminal box Site washdown pump Maximum around pump 4 40 Feed Water Pump (11 kv, 6 MW) Pump surface - booster end * Falling to 100% at 0.3 m Falling to 100% at 0.1 m Falling to 100% at 0.2 m 43

52 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK This page is intentionally blank 44

53 APPENDIX D APPENDIX D Measurement Results Connah s Quay Power Station The survey at Connah s Quay Power Station was carried out on 26 May 2016 between 10:30 and 15:30. During most of this time (c. 11:00 to 14:30) the generator on Unit 1 was operating at a maximum output of 325 MW and measurements were directed towards the generator and associated power distribution system. The ancillary equipment was addressed before this time and the SFC transformer, 400 kv lines and Control Building after this time when the output had reduced to 230 MW. The results of measurements of maximum magnetic field strengths and electric field strengths (as percentages of the action levels in the EMF Directive and in the Council Recommendation 1999) are presented below. Results greater than or equal to 100% of the relevant level are presented in red font, those between 50% and 100% are presented in amber font. D1 Routine Generation No measurements of electric field strength were made around the generators as all of the associated conductors are insulated, with the electric field contained within the insulating medium. Magnetic field strength measurements were made around the Unit 1 generator and associated excitation systems. D1.1 Excitation System The magnetic field was slightly in excess (110%) of the low action levels close to the cables at the rear of the excitation disconnection switch. The field also approached the high action levels (87%) in the localised region close to the cables and exceeded (160%) the limb action levels in contact with these cables (see Table D2). Although field strengths were too localised to result in whole body exposures, precautions should be taken to prevent touching of conductors (see Section 6.2 of the main report). The spectral content of the magnetic fields measured at the rear of the Unit 1 Excitation Disconnection switch is shown in Figure D1. The spectrum is dominated by the fundamental frequency of 50 Hz, although there are significant contributions from higher frequency harmonics. The magnetic field exceeded the Council Recommendation in localised regions around the excitation system cabinets (see Tables D1 and D2). It is likely that the fields also exceeded the within the exclusion zone (hatched area) close to the generator, although measurements could not be made here due to the potentially explosive atmosphere. Precautions should therefore be taken with regard to the access of employees at particular risk into these regions (see Section 6.2 of the main report). 45

54 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D1 Maximum magnetic flux densities measured around Unit 1 Static Excitation System expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Front mid-section Front mid-section 0.5 m from floor Front RH 5 40 RH side Back LH 7 7 Back mid-section Back mid-section 0.5 m from floor LH side <1 20 Inside control cubical on LH side <1 20 * Measurements made at chest height approximately 0.1 m from unit (in an anti-clockwise direction) Table D2 Maximum magnetic flux densities measured around Unit 1 Excitation Disconnection Switch expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Front mid-section Back mid-section Back RH side 0.15 m from floor next to cables Back RH side at floor level in close contact with cables On floor between Excitation Disconnection Switch and Static Excitation System * * 86% high action level; 160% limb action level Spectral content shown in Figure D1 46

55 APPENDIX D Figure D1 Spectral content of magnetic fields from rear of Unit 1 Excitation Disconnection Switch D1.2 Generator Measurements of accessible magnetic flux density were made around the Unit 1 generator and are presented in Table D3. The spectral content of the magnetic fields measured at the end of the Unit 1 generator housing is shown in Figure D2. The spectrum is dominated by the fundamental frequency of 50 Hz. Table D3 Maximum magnetic flux densities measured around Unit 1 Generator expressed as a percentage of the low action levels and Council Recommendation reference levels Measurement Location % Low action levels % Council Recommendation Inside steam turbine acoustic enclosure* 3 7 Edge of exclusion zone on LH side of generator* Housing next to acoustic enclosure <1 6 Mid-section of generator housing <1 7 RH of generator housing 1 9 End of generator housing LH side of DC brush gear 47

56 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D3 Maximum magnetic flux densities measured around Unit 1 Generator expressed as a percentage of the low action levels and Council Recommendation reference levels Measurement Location % Low action levels % Council Recommendation At 0.1 m 4 50 At 0.5 m 3 32 Front of DC brush gear 2 19 Small lubrication oil generator on exciter end (150 kva) LH side 1 10 Front (open end) 1 10 RH side 2 38 At cable to connection box 2 33 * Measurements made at chest height Spectral content shown in Figure D2 Figure D2 Spectral content of magnetic fields at end of Unit 1 generator housing 48

57 APPENDIX D D2 Power Distribution Measurements of electric field strength were made around the Unit 1 isolated phase bus, generator transformer compound; in the offices of the adjacent Control Building; inside the banking compound; and beneath the National Grid overhead lines, which cross back over the site. D2.1 Isolated Phase Bus Measurements of magnetic flux density were made at the closest points of access to the isolated phase bus from the Unit 1 generator. The results of these measurements are presented in Table D4. Table D4 Maximum magnetic flux densities measured around Unit 1 isolated phase bus expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Red phase 0.1 m from voltage transformer at chest height Below lower section of conductor feeding low voltage transformer Yellow phase LH side of lower section of conductor feeding low voltage transformer Directly under main isolated phase bus at chest height D2.2 Generator Transformer Compound Measurements of both electric field strength (Table D5 and D6) and magnetic flux density (Table D7) were made in and around the Unit 1 generator transformer compound. The electric field was much less than the low action levels at all locations and only reached half (56%) of the Council Recommendation 5 m outside the Unit 1 transformer generator compound beneath the low-point of the conductors (Table D6). The magnetic flux density measured in and around the Unit 1 generator transformer compound was less than the low action levels at all positions, although it did exceed the Council Recommendation inside the acoustic housing (Table D7). 49

58 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D5 Maximum electric field strength measured inside the Unit 1 generator transformer compound expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Below red phase conductor Below yellow phase conductor Below blue phase conductor * Measurements made approximately 2.8 m from fencing with probe positioned 2 m above ground level 8% of high action level 6% of high action level 7% of high action level Table D6 Maximum electric field strength measured outside Unit 1 generator transformer compound expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Below red phase conductor Below yellow phase conductor Below blue phase conductor * Measurements made approximately 5 m from fencing with probe positioned 2 m above ground level 12% of high action level 7% of high action level 14% of high action level Table D7 Maximum magnetic flux densities measured in and around Unit 1 generator transformer compound expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Measurements made inside the acoustic housing at 0.1 m from unit (in an anti-clockwise direction) Front of unit RH side front of unit (blue phase) RH side middle of unit (yellow phase)

59 APPENDIX D Table D7 Maximum magnetic flux densities measured in and around Unit 1 generator transformer compound expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation RH side back of unit (red phase Back of unit LH side back of unit (red phase) 6 70 LH side middle of unit (yellow phase) LH side front of unit (blue phase) Measurements made around acoustic housing at 0.1 m from wall LH side back (red phase) LH side middle (yellow phase) LH side front (blue phase) 2 20 Measurements made at fencing opposite acoustic housing at 1 m from fence Below red phase conductor <1 7 Below yellow phase conductor Below blue phase conductor <1 3.7 Measurements made outside compound approximately 5 m from fencing Below red phase conductor <1 5.8 Below yellow phase conductor <1 6.6 Below blue phase conductor <1 6 * All measurements made at chest height D2.3 Control Building Measurements of electric (Table D8) and magnetic (Table D9) fields were also made in an office at the south-east corner on the third floor of the Control Building. This office was the closest point to the Unit 1 conductors. 51

60 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D8 Maximum electric field strength measured in south-east corner office on Third Floor of Control Building expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation At window closest to Unit 1 conductors <1 <1 * Measurements made approximately 2 m above floor level Table D9 Maximum magnetic flux density measured in south-east corner office on Third Floor of Control Building expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation At window closest to Unit 1 conductors <1 1 D2.4 Unit 1 SFC Transformer The results of measurements of magnetic flux density around the Unit 1 SFC transformer are presented in Table D10. The measured magnetic flux densities were below both the low action levels and Council Recommendation at all positions. Table D10 Maximum magnetic flux densities measured around Unit 1 SFC transformer (9.4 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Front of unit 3 6 RH side of unit (at earth conductors) 4 48 RH side back of unit 3 16 Back of unit at cables at waist height 3 15 Back of unit at cables at floor level 3 19 LH side of unit 3 16 * Measurements made at 0.1 m from unit and unless otherwise stated at chest height 52

61 APPENDIX D D2.5 Turbine Hall Transformer The results of measurements of magnetic flux density around the Unit 1 Turbine Hall Transformer are presented in Table D11. The measured magnetic flux densities were less than the low action levels and Council Recommendation at all positions. Table D11 Maximum magnetic flux densities measured around Unit 1 Turbine Hall small transformer (6.6 kv to 415 V, 1.25 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Front of unit 3 35 RH side of unit 3 29 Back of unit 3 42 LH side of unit <1 7 * Measurements made at 0.1 m from surface of unit at chest height D kv Switch Rooms Magnetic flux densities were assessed in two 6.6 kv switch rooms associated with Unit 1. The results are presented in Tables D12 and D13. Where a value of 100% of the is indicated in these tables the entry is generally intended to show the distance at which the magnetic flux density reaches this value. With one exception, the magnetic flux densities in the vicinity of the 6.6 kv switchgear were less than the low action levels. The one exception to this was in contact with the cables from the Unit 1 Transformer feeding the 6.6 kv switch room, where the field was slightly in excess (110%) of the low action levels over a very localised region that would not give rise to whole body exposures. These were the same cables that had generated strong fields in the generator transformer compound. However, in some of these locations there were localised regions where the Council Recommendation reference level was exceeded. The reference level was exceeded by a factor of almost four (390%) close to the cable array from the transformer feeding the 6.6 kv switch room (see Table D12). There were also other localised regions where the magnetic flux density was around the reference level. Precautions should therefore be taken with regard to the access of employees at particular risk into these regions (see Section 6.2 of the main report). 53

62 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D12 Maximum magnetic flux densities measured in the Unit 1 Transformer 6.6 kv switch room (21 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation RH side of unit at chest height 2 22 Back of unit at chest height 3 26 Back cable on LH side at waist height Middle cable on LH side at waist height Front cable on LH side at waist height In contact with middle cables* at waist height * Cable current A as measured with current clamp 31% of high action level 14% of limb action level Table D13 Maximum magnetic flux densities measured in the Unit kv switch room (21 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation 6.6 kv switchgear Front of unit 1 15 RH side of unit <1 5 Back of unit 3 50 Back of unit at RH side approximately 0.15 m from floor LH side of unit at back approximately 0.15 m from floor LH side of unit kv switchgear Front of unit <1 5 RH side of unit

63 APPENDIX D Table D13 Maximum magnetic flux densities measured in the Unit kv switch room (21 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Back of unit <1 9 LH side of unit <1 8 D V Switch Room Magnetic flux densities were also assessed in the 415 V switch room and the results of these measurements are presented in Table D14. Again there were localised regions where magnetic flux densities were close to or just above the Council Recommendation reference levels. Table D14 Maximum magnetic flux densities measured in the Unit 1 Turbine Hall 415 V switch room (2.5 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation Cabinets on LH of Transformer A 1 12 LH of Transformer A door 3 44 LH of Transformer A door approximately 0.5 m from floor LH of Transformer A door approximately 2 m from floor RH of Transformer A door 2 42 RH of Transformer A door approximately 0.5 m from floor RH of Transformer A door approximately 2 m from floor Cabinets between Transformers A and B LH of Transformer B door 2 29 LH of Transformer B door approximately 0.5 m from floor LH of Transformer B door approximately 2 m off floor

64 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D14 Maximum magnetic flux densities measured in the Unit 1 Turbine Hall 415 V switch room (2.5 MVA) expressed as a percentage of the low action levels and Council Recommendation Measurement Location % Low action levels % Council Recommendation RH of Transformer B door 2 36 RH of Transformer B door approximately 0.5 m from floor RH of Transformer B door approximately 2 m from floor Cabinets on RH of Transformer B 1 12 RH of back of Transformer B <1 5 Back of Transformer B Back of Transformer A LH of back of Transformer A m from LH end cabinet of unit <1 15 * Measurements made at 0.1 m from surface of units at chest height D2.8 Banking Compound Measurements of electric field strength (Table D15) and magnetic flux density (Table D17) were made in the Unit 1 areas of the banking compound and beneath the outgoing 400 kv conductors (Tables D16 and D18). The electric field exceeded the low action levels (130%) beneath the low-level exposed conductors within the banking compound, but did not exceed the high action levels (64%) (see Table D15). The field was also more than twice (250%) the Council Recommendation. Precautions should therefore be taken with regard to the access of employees into the banking compounds (see Sections 6.1 and 6.2 of the main report). The electric field strength reached over half (65%) of the low action levels on the grass beneath the 400 kv lines. At the same position the field strength exceeded (130%) the Council Recommendation reference level (see Table D16), which is applicable to exposures of the general public. This is of significance since the grass area has in the past been used for staff social events. It is recommended, therefore, that this area under the 400 kv lines should no longer be used for public events. The magnetic flux density measured in the Unit 1 area of the banking compound and beneath the outgoing 400 kv overhead lines was less than the low action levels. In addition, the flux density was also well below the Council Recommendation. The spectral 56

65 APPENDIX D content of the magnetic fields measured below the south line on the grass area is shown in Figure D3. The spectrum is dominated by the fundamental frequency of 50 Hz. Table D15 Maximum electric field strength measured inside Banking Compound expressed as a percentage of the low action levels and Council Recommendation reference levels Measurement Location* % Low action levels % Council Recommendation Below red phase low-level swan-neck conductor Below yellow phase low-level swanneck conductor Below blue phase low-level swanneck conductor * Measurements made approximately 2 m above ground level 64% of high action level 53% of high action level Table D16 Maximum electric field strength measured beneath 400 kv outgoing conductors crossing over staff car park expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Below lowest point of south line Below lowest point of north line 7 14 Below south line on grass area approximately 3.5 m from path to car park * Measurements made approximately 2 m above ground level 57

66 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D17 Maximum magnetic flux density measured inside Banking Compound expressed as a percentage of the low action levels and Council Recommendation reference levels Measurement Location* % Low action levels % Council Recommendation Below red phase low level swan neck conductor Below yellow phase low level swan neck conductor Below blue phase low level swan neck conductor Next to yellow phase current transformer Next to red phase current transformer 1 11 Below red phase high level straight conductor Below yellow phase high level straight conductor Below blue phase high level straight conductor <1 5 <1 5 <1 7 * Measurements made at head height Table D18 Maximum magnetic flux density measured beneath 400 kv outgoing conductors crossing over staff car park expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Below lowest point of south line <1 4 Below lowest point of north line <1 2 Below south line on grass area approximately 3.5 m from path to car park <1 4 * Measurements made at head height Spectral content shown in Figure D3 58

67 APPENDIX D Figure D3 Spectral content of magnetic fields below south line on grass area D3 Ancillary Equipment No measurements of electric field strength were made around the ancillary equipment as all of the associated conductors are insulated, with the electric field contained within the insulating medium. D3.1 Unit 3 HP Feed Pump Magnetic flux densities around the 1.9 MW Unit 3 HP Feed Pump were assessed and the results are presented in Table D19. The magnetic flux densities were less than both the low action levels and the at all positions. Table D19 Maximum magnetic flux density measured around Unit 3 HP Feed Pump (1.92 MW, 6.6 kv) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation RH side at back 1 12 RH side in middle 3 29 RH side at front 2 18 Front by air intake grille <1 2 59

68 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK Table D19 Maximum magnetic flux density measured around Unit 3 HP Feed Pump (1.92 MW, 6.6 kv) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation LH side at front 2 14 LH side in middle 1 14 LH side at back <1 7 Front of connection box on RH side of unit Top of connection box 0.15 m from cables * Measurements made at 0.1 m from unit and unless otherwise stated at chest height D3.2 Unit 3 Cooling Water Pump Magnetic flux densities around the 980 kw Unit 3 Cooling Water Pump were assessed and the results are presented in Table D20. The magnetic flux density was less than the low action levels and Council Recommendation at all locations. Table D20 Maximum magnetic flux density measured around Unit 3 Cooling Water Pump (980 kw, 6.6 kv) expressed as a percentage of the low action levels and Council Recommendation Measurement Location* % Low action levels % Council Recommendation Ground level around pump <1 <1 Ground level at drive shaft <1 2 Upper level in front of motor <1 4 Upper level below motor in contact with cable 2 20 Upper level RH side of motor <1 4 Upper level RH of front of unit <1 1 Upper level RH side of unit <1 <1 * Measurements made at 0.1 m from unit and unless otherwise stated at chest height 60

69 APPENDIX E APPENDIX E Measurement Results Didcot B Power Station During the survey the generator was operating at maximum output, with the two Gas Turbines 61 and 62 (GT61 and GT62) operating at 205 MW each and Steam Turbine 60 (ST60) operating at 222 MW. The results of measurements of maximum magnetic field strengths and electric field strengths (as percentages of the low action levels and Council Recommendation ) are presented below. Results greater than or equal to 100% of the relevant level are presented in red font, those between 50% and 100% are presented in amber font. E1 Routine Generation Magnetic flux densities were surveyed around the ST60 steam turbine excitation system. However, as access was not possible within the gas control area, measurements were also made around the GT61 gas turbine generator together with its exciter and neutral cables. E1.1 Steam Turbine Excitation Room Results of the magnetic flux density survey are presented in Table E1 below. The spectral content of the magnetic field was measured in the excitation room and is presented in Figure E1 below. It can be seen from this figure that although the fundamental frequency at 50 Hz is the dominant component, there are significant contributions from higher frequency harmonics. A schematic drawing of the steam turbine excitation room, showing the approximate extent of the areas where the Council Recommendation are exceeded is given in Figure E2. Table E1 Maximum magnetic flux densities measured in the ST60 steam turbine excitation room, expressed as percentages of the low action levels and Council Recommendation Measurement location % low action level % Council Recommendation reference level Side of transformer cage * Cables outside transformer cage > Exciter cabinet Common neutral cabinet 1 52 Common neutral cable 2 53 Cables from transformer in corner of room

70 ASSESSMENT OF ELECTRIC AND MAGNETIC FIELD EXPOSURE FROM POWER GENERATION FOR ENERGY UK * Falling to 100% of the at 0.95 m 140% of the limb action levels in hand accessible areas close to the cables Falling to 100% of low action levels at 0.4 m Maximum of 150% of high action levels falling to 100% at 0.35 m Falling to 100% of at 2 m Figure E1 Spectral content of magnetic fields in the steam turbine excitation room 62

71 APPENDIX E Figure E2 Plan of steam turbine excitation room, showing the approximate extent of the area where Council Recommendation are exceeded E1.2 Gas Turbine Exciter Control Cabinet PCC Switch Room Measurements of magnetic flux density were made around the exciter supply cabinet for gas turbine GT61 during routine operation. The results are presented in Table E2. Results of measurements of the spectral content of magnetic fields associated with the excitation cabinet during routine operation can be seen in Figure E3 below. It can be seen that although the dominant component is at 50 Hz, there is considerable harmonic content, which extends to high frequencies. Table E2 Maximum magnetic flux densities measured around the GT61 gas turbine exciter control cabinet in the PCC switch room, expressed as percentages of the low action levels and Council Recommendation Measurement location % low action level % Council Recommendation reference level Front of cabinets 2 90 Back of cabinets BTL Battery charger