D e s i g n a n d c o n f i g u r a t i o n s t a n d a r d

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1 D e s i g n a n d c o n f i g u r a t i o n s t a n d a r d 132 kv 400 kv Installation of underground AC cables in urban areas EDS-0074 Document title EDS-0074 Rev 0 Installation of underground AC cables in urban areas Document no. 13/ Target group Electricity Transmission and external suppliers Valid until 1 November 2019 Revision Document Author Reviewer Approver status Name Date Name Date Name Date TSA, HSL, 0 Approved RAO SSV, JDV, MGB, PJH, XEJA JSC Table of contents 1. Scope/introduction Abbreviations and definitions References and standards General Health and safety requirements Environmental requirements Quality requirements Dependencies and conditions Performance requirements Technical requirements Design requirements Decoupling of excavation works and cable installation Cable system installation design Drum lengths Cable system formation Earth continuity conductor Earth potential rise near tall objects Optical fibres for temperature and vibration measurements and communication Optical fibres for PD measurements Generic cable route profile Cable trench, joint bay and horizontal directional drillings Installation conditions Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 1/16

2 8.2 Cable trench Joint bay Horizontal directional drillings Optical fibres for PD measurements Earth continuity conductor Installation conditions Cable installation Installation of ducts Cable installation water push-pull Cable installation winch pulling Joint installation Handover testing Spare parts Documentation Appendices Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 2/16

3 1. Scope/introduction This technical design standard specifies Energinet s technical requirements for installation of underground High Voltage (HV) and Extra High Voltage (EHV) cables in urban areas. The standard is intended to be used during tendering for new cables, tendering for test of cable systems, tendering for installation of cables, etc. The standard ensures a unified approach to component and installation design and ensures that all relevant parts of Energinet agree on the requirements. Furthermore, this standard specifies that Energinet, cable manufacturers, accessories manufacturers, cable installers, civil contractors, etc. agree on a common set of criteria for cable installation. In that way, all interfaces related to cable installation should be clarified. It should be noted that this standard is related only to the cable installation in urban areas. Bonding equipment and auxiliary equipment are standardised in Energinet standard ETS-0054, cables are specified in ETS-0066, and accessories are standardised in ETS Installation of underground AC cables in rural areas is specified in EDS-0075, and cable system design is standardised in EDS Abbreviations and definitions DS/EN ECC EDS EGS EHV EKS ETS HDD HV IEC ISO PD Danish Standard Earth continuity conductor Energinet design standard Energinet guideline Extra high voltage Energinet concept Energinet technical standard Horizontal directional drilling High voltage International Electrotechnical Commission International Standards Organization Partial discharge 2. References and standards 2.1 General Design of HV and EHV cables must in general be based on the most recent version of the applicable DS/EN standards, DS/IEC standards, IEC standards, and Cigré recommendations, including (but not limited to): DS/EN 60228:2006 Conductors of insulated cables IEC :2006 Electric cables Calculation of the current rating Part 1-1: Current rating equations (100 % load factor) and calculation of losses General Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 3/16

4 IEC :2006/AMD1:2014 Amendment 1 Electric cables Calculation of the current rating Part 1-1: Current rating equations (100 % load factor) and calculation of losses General IEC :1993 Electric cables Calculation of the current rating Part 1: Current rating equations (100 % load factor) and calculations of losses Section 2: Sheath eddy current loss factors for two circuits in flat formation DS/IEC :2002 Electric cables Calculation of the current rating Part 1-3: Current rating equations (100 % load factor) and calculation of losses Current sharing between parallel single-core cables and calculation of circulating current losses DS/IEC :2015 Electric cables Calculation of the current rating Part 2-1: Thermal resistance Calculation of the thermal resistance IEC :1995 Electric cables Calculation of the current rating Part 2: Thermal resistance Section 2: A method for calculating reduction factors for groups of cables in free air, protected from solar radiation DS/IEC :2017 Electric cables Calculation of the current rating Part 2-3: Thermal resistance Cables installed in ventilated tunnels DS/IEC :2017 Electric cables Calculation of the current rating Part 3-1: Operating conditions Site reference conditions IEC :2012 Electric cables Calculation of the current rating Part 3-2: Sections on operating conditions Economic optimization of power cable size IEC :2007 Electric cables Calculation of the current rating Part 3-3: Sections on operating conditions Cables crossing external heat sources DS/IEC 60840:2012 Power cables with extruded insulation and their accessories for rated voltages above 30 kv (U m = 36 kv) up to 150 kv (U m = 170 kv) Test methods and requirements IEC :1985 Calculation of the cyclic and emergency current rating of cables. Part 1: Cyclic rating factor for cables up to and including 18/30(36) kv IEC :1985/AMD1:1994 Amendment No. 1 IEC :1985/AMD2:2008 Amendment 2 Calculation of the cyclic and emergency current rating of cables Part 1: Cyclic rating factor for cables up to and including 18/30 (36) kv IEC :1989 Calculation of the cyclic and emergency current rating of cables. Part 2: Cyclic rating of cables greater than 18/30 (36) kv and emergency ratings for cables of all voltages IEC :1989/AMD1:2008 Amendment 1 Calculation of the cyclic and emergency current rating of cables Part 2: Cyclic rating of cables greater than 18/30 (36) kv and emergency ratings for cables of all voltages DS/IEC :2002 Calculation of the cyclic and emergency current rating of cables Part 3: Cyclic rating factor for cables of all voltages, with partial drying of the soil DS/IEC 62067:2012 Power cables with extruded insulation and their accessories for rated voltages above 150 kv (U m = 170 kv) up to 500 kv (U m =550 kv) Test methods and requirements Cigré TB 283:2005 Special bonding of high voltage power cables Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 4/16

5 Cigré TB 303:2006 Revision of qualification procedures for high voltage and extra high voltage AC extruded underground cable systems Cigré TB 347:2008 Earth Potential Rises in specially bonded Screen Systems Cigré TB 446:2011 Advanced design of metal laminated coverings: recommendation for tests, guide to use, operational feed back Cigré TB 531:2013 Cable Systems Electrical Characteristics Cigré TB 560:2013 Guideline to Maintaining the Integrity of XLPE Cable Accessories Furthermore, at least the following Energinet standards should be taken into account in reference to underground HV and EHV cables: EDS-0075 Installation of underground AC cables in rural areas EDS-0077 Design of underground AC cable systems ETS-0054 Bonding equipment and auxiliary equipment for underground AC cable systems ETS-0066 Underground AC cables ETS-0067 Accessories for underground AC cables EGS-0084 Underground AC cables - cable data sheet EGS-0085 Underground AC cables - joint data sheet EGS-0086 Underground AC cables - termination data sheet 2.2 Health and safety requirements Cable installation must be designed in a way that takes health and safety into consideration to the absolute highest possible level for everybody involved in design, production, transport, installation, commissioning, operation, maintenance, and decommissioning of the cable system. 2.3 Environmental requirements Cable installation must be designed in a way that takes environmental aspects into consideration to the absolute highest possible level. This means that cable installation must be designed to minimise the environmental impact on the entire lifecycle of the cable system, including design, production, transport, installation, commissioning, operation, maintenance, and decommissioning of the cable system. 2.4 Quality requirements In addition to the standard ISO certificates, etc., Energinet expects installation to be carried out in a way making it possible to trace the quality of the cable and all equipment and tools used to the greatest possible extent along the entire cable route. This will enable a better and more accurate root cause analysis in case of future cable failures. 3. Dependencies and conditions Section intentionally left blank; Dependencies and conditions specified elsewhere. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 5/16

6 4. Performance requirements Section intentionally left blank; Performance requirements specified elsewhere. 5. Technical requirements Section intentionally left blank; Technical requirements specified elsewhere. 6. Design requirements The cable system must be designed and manufactured for a lifetime of at least 40 (forty) years, and the process of cable installation must not reduce this expected lifetime. This means that equipment/components installed with the cable system, from (and including) termination to (and including) termination, must also be able to sustain 40 (forty) years, and that equipment used for installation must not influence the 40-year lifetime expectancy of the cable system. The methods described in EDS-0075 must be used to the greatest possible extent, as they are considered as price effective compared to the methods suggested in the present standard. The methods described in EDS-0075 require, however, that the cable route is clear of large obstacles, and that it is to a great extent possible to have long open trenches. This is not possible in urban areas where issues, such as traffic regulation, crossing of a significant amount of third-party lines (e.g. power cables, optical fibres, district heating, water, gas), etc., restrict the length of an open trench. The present standard, therefore, describes methods to overcome these obstacles to optimise the relationship between price, techniques, time schedules, etc. Energinet is open to new installation methods. However, if other methods are suggested, Energinet, cable manufacturers, accessories manufacturers, cable installers, civil contractors, etc. must agree on the terms. It should be noted that cables will be installed in air temperatures down to -5 o C. 6.1 Decoupling of excavation works and cable installation As stated, the most important reasons for performing cable installation differently in urban areas compared to rural areas are: It is not possible to have long trenches open at a time Crossing under and over a significant amount of other lines is required. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 6/16

7 Therefore, it is necessary to decouple the excavation works and the cable installation. Different methods for this are described in the following. The order of priority in the installation method is: 1. Installation in open trench/with digging box, if at all possible and reasonable 2. Installation in ducts a. With water pressure b. With wire pull 3. Installation in tunnel. The open trench and digging box methods are described in EDS-0075 and, therefore, not further described in the present document. Installation in tunnel is presently a very expensive method and is at best to be applied to a few cable systems only. This method is, therefore, not further described in the present document, and the method will have to be developed and described on a project basis. Consequently, the following sections focus mostly on installing cables in ducts. Cables to be installed in ducts must be equipped with a pulling head. 7. Cable system installation design For design of the cable system itself, including accessories, etc., reference is made to EDS Drum lengths Cable systems must be designed so that it is possible to install the cables within a reasonable timespan. Therefore, a maximum of 1200 m for drum lengths must be considered as standard. 7.2 Cable system formation Cables in urban areas will as standard be installed in close trefoil formation or in duct trefoil formation with a trench cross section according to the following drawings: 13L /150 kv duct installation 13L /150 kv direct installation 13L kv duct installation 13L kv direct installation These drawings present the entire cable trench, including all cover plates, warning nets, location of fibres, etc. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 7/16

8 7.2.1 Earth continuity conductor If the cable system design prescribes the use of an ECC along part of the cable route, or the entire cable route, the installation conditions must be as follows. The ECC must be laid parallel and as close as possible to the cable system, and also transposed at an equal distance between consecutive earthed points (Figure 1 and Figure 2). If the symmetry in the transposition cannot be complied with, calculations of circulating currents must be performed to ensure that lowering of the system ampacity does not occur. Figure 3 shows an example of a three-line diagram for a single-point-bonded system (flat configuration) with ECC. In case two ECCs are installed, the second ECC must be laid symmetrically to the first, which must be installed according to what is stated above. Figure 1 - Transposition of ECC for trefoil formation. a) First half of the cable route, b) Second half of the cable route Figure 2 - Transposition of ECC for trefoil formation in ducts. a) First half of the cable route, b) Second half of the cable route Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 8/16

9 2/3 d 2/3 d Single Core Bonding Lead Earth Continuity Conductor (ECC) Single Phase SVL Box Single Phase Grounding Box Cable Termination Figure 3 - Schematic of single-point bonding methodology, including transposing of ECC, cables in flat configuration Earth potential rise near tall objects In case the cable system route runs past a tall object, e.g. an overhead line tower, a wind turbine, etc., it is necessary to protect the cable jacket from pin holes, which may arise if the tall object is struck by lightning. Calculations performed for Energinet 1 show that it should to the greatest possible extent be avoided to run past a tall object at a distance lower than 50 metres between the cable and the object. Depending on the distance between cable and tall object, the following precautions must be put in place: Distance [m] Protective measure <15 Foundation of tall object must be extra earthed by applying seven bare copper wires of at least 95 mm 2 each with a length of 30 m. The wires must be installed in a half-star formation away from the HV/EHV cable, see Figure 4. Furthermore, it is necessary to install one bare copper ECC conductor of 300 m (150 m on each side of the tall object) of at least 95 mm 2 per cable phase. These bare ECCs must be installed 0.1 m (centre-to-centre) from each HV/EHV cable phase on the side closest to the tall object It is necessary to install one bare copper ECC conductor of 300 m (150 m on each side of the tall object) of at least 95 mm 2 per cable phase. These bare ECCs must be installed 0.1 m (centre-to-centre) from each HV/EHV cable phase on the side closest to the tall object. 1 Reference is made to an internal Energinet document 13/ Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 9/16

10 30-50 It is necessary to install one bare copper ECC conductor of 300 m (150 m on each side of the tall object) of at least 95 mm 2 along the outer cable phase. This bare ECC must be installed 0.1 m (centre-to-centre) from the HV/EHV cable phase on the side closest to the tall object. >50 No protective measures needed. HV/EHV cable Foundation of tall object Figure 4 - Added earthing of the foundation of the tall object Optical fibres for temperature and vibration measurements and communication When specified that a communication (and measurement) fibre is required for any cable system, an optical fibre will be installed according to Figure 5. a) b) Figure 5 - Placement of optical fibre for communication and temperature and vibration monitoring. a) Fibre for cables installed in a duct, b) Installed next to the trefoil formation Optical fibres for PD measurements When specified that PD measurements of joints are required for any cable system, an extra optical fibre cable will be installed for transferring data. This optical fibre will be installed on the outside of one of the outer phases, see Figure 6. a) b) Figure 6 - Placement of optical fibre for PD monitoring. a) PD fibre for cables installed in a duct, b) Installed next to the trefoil formation. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 10/16

11 7.3 Generic cable route profile As standard, it must be possible to install the cable in a cable route with the profile as described in Table 1. The profile is an artificial cable route used for calculations only. Distance from cable Route profile specification drum [m] 0 3 kn pushing with Caterpillar m HDD installation. For close trefoil formation, PE ducts are SDR 17 Ø250 mm (outer diameter). For cable systems in ducts, the same ducts are used also for HDDs. Curved installation, maximum installation depth below ground surface 10 m o left bend with a radius of 5.0 m o right bend with a radius of 5.0 m Elevation of 10 m o right bend with a radius of 5.0 m 1200 End of cable pull Table 1 - Profile of cable route which the cable must be able to sustain with the different installation methods. 8. Cable trench, joint bay and horizontal directional drillings 8.1 Installation conditions It is assumed that the temperature at normal burial depth (from 1-2 metres) is 20 o C. It is assumed that the soil is dry, as in many cases it will be under asphalt, and limited amounts of water can penetrate. Consequently, for urban installations, there are no limitations on the jacket/duct outer temperature, and the ampacity can, therefore, be based solely on the maximum allowed conductor temperature. The properties stated in Table 2 must be assumed for e.g. cable dimensioning. Material Thermal resistivity [Km/W] Specific heat [J/Km 3 ] Soil (top soil, sub soil, etc.) 2.0 2,000,000 Thermal backfill (sand used in 0.8 2,000,000 trenches, etc.) (value will be tested for every 1000 m 3 ) Concrete 0.5 2,000,000 Bentonite (used for filling of HDDs) 0.7 2,000,000 Table 2 - Thermal properties used for cable dimensioning, etc. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 11/16

12 8.2 Cable trench For both the open trench and digging box installation methods, the construction sites must be designed as shown in the following drawings: In urban areas where traffic can be expected, the working area will be equipped with barriers (e.g. fences), and the area will look as specified in drawing 13L In very special cases where space does not allow for a wide working area as described in 13L , the method specified in drawing will be used 13L In cases where traffic is not expected, work is expected to be carried out in accordance with EDS Joint bay Joint bays will be excavated as the normal trench, i.e. no extra space, as the jointing is suggested to be performed above ground. However, joint bays may be up to 0.5 metres deeper than the rest of the cable route in order to ensure room for thermal expansion of the cables, etc. After jointing, the joints will be lowered into the trench. The standard manhole for link boxes in urban areas will be as specified in drawing 13L The standard manhole for optical fibre boxes will be as specified in drawing 13L Horizontal directional drillings Horizontal directional drillings (HDDs) are commonly used for crossing under roads, train tracks, rivers, etc., and the installation will be as shown in drawing 13L This drawing presents the entire HDD, including location of communication fibres, etc Optical fibres for PD measurements When specified that PD measurements are required for any cable system, an extra optical fibre cable will be installed for transferring data. This optical fibre will be installed in one of the outer HDD ducts together with the HV/EHV power cable Earth continuity conductor If the cable system design prescribes the use of an ECC along part of the cable route, or the entire cable route, the installation conditions must be as follows. To the greatest extent possible, the ECC will be installed in the outer duct together with the HV/EHV power cable. If there are two or more HDDs within one minor section, the ECC may alternate position between the two outer phases in order to even out asymmetry as much as possible. In this case, and if the symmetry in the transposition for other reasons cannot Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 12/16

13 be complied with, calculations of circulating currents must be performed to ensure that excessive deterioration of the system ampacity does not occur Installation conditions Standard HDD pipes used are PE Ø250 mm (outer diameter) SDR 17 PN10. For cables systems installed mainly in ducts, the same ducts are used also for HDDs. As standard for installing HDDs in flat formation, Energinet plans according to Table 3. Installation depth [m] Centre-to-centre spacing [m] Temperature [ o C] Linear interpolation between 5 m at 20 o C and 10 m at 15 o C > Table 3 - Installation conditions in HDD To reduce friction, lubricant is applied to the cable surface before entering the duct. After cable installation, the spacing between cable surface and duct inner surface will be filled with: Bentonite for ducts with inner diameters larger than 2 x diameter of cable Clean water for ducts with inner diameters of up to 2 x diameter of cable It should, however, be noted that it cannot be guaranteed that water is present for the entire lifetime of the cable. 9. Cable installation In general, the maximally allowed pulling forces and tensions must be respected. As standard, it is assumed that the following values can be sustained by the cable: Maximum pulling force for straight pulls: 30 N/mm 2 for aluminium conductors 50 N/mm 2 for copper conductors Maximum sidewall pressure: Sidewall pressure in bends to which the cable can be exposed is up to 2500 DaN/m Maximum radial roller tension: Tension on the cable from each roller is up to 100 DaN/roller Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 13/16

14 9.1 Installation of ducts The ducts used must have an inner diameter as close to and at least 1.5 times the outer diameter of the cable. Depending on the cable route, the longest possible trench is opened, and ducts are connected on the ground (e.g. by means of butt welding, compression connectors, etc.) in the longest possible sections. Depending on the cable route, as long a trench as possible is opened, and ducts are connected on the ground (e.g. with butt welding, compression connectors, etc.) in the longest possible lengths. The ducts are then pulled into the trench. Each section is subsequently connected to the next section inside the trench (e.g. with compression connectors, electrowelded joints, etc.). The supplier of the ducts will propose the most appropriate duct jointing techniques. The choice of jointing techniques must be based on health and safety, reliability of jointing works, time, price, complexity, etc. Ducts have an individual length of metres; therefore, metres is the expected lower limit of open trench length. 9.2 Cable installation water push-pull Cables installed with the water pressure method must be able to sustain the water pressure, the pulling tension and the sidewall pressures expected in the ducts. Ducts with a maximum pressure of 10 bars will be installed; therefore, the cable must also be able to sustain 10 bars of pressure for the short time it takes to install the cables in the duct (up to 10 hours). This requirement also relates to end caps, pulling heads, etc. The cable must be able to sustain the lubricants used for this, e.g. soft soap or a siliconebased lubricant. The method is presented in Figure 7. Figure 7 - Water push-pull method The cable pulling head is connected to a pulling pig with a flexible strap, and a caterpillar at the inlet will be pushing the cable into the ducts. The water then pulls at the pig, which then pulls the cable through the ducts. Ducts must be installed with an over length (as much over length as is needed for the cable) at the outlet, as it is not possible to pull more cable out than what initially comes out of the duct. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 14/16

15 It is possible that Energinet chooses to install multiple cable sections from the same joint bay. This will mean that some of the cables will be transported to the final destination by the free-floating technique, see Figure 8. Figure 8 Free-floating technique The cable must, before free floating is initiated, be cut into its final length, and a pulling head must be installed. A rear pig is attached to the rear pulling head, and the cable is then pushed through the ducts, as tube post, until it reaches its final position. Water tanks and pumps must be installed in the joint pits in order to ensure that the water, to the greatest possible extent, is recycled among the different cable sections, and that no water is spilled into or inside the joint pits. Any water, which is collected at the end of the installation campaign, must be disposed of properly, as it must be considered as contaminated. 9.3 Cable installation winch pulling An alternative to the water pressure method is the use of a winch, pulling the cables into the ducts. The forces (pulling tension, sidewall pressure, etc.) are expected to be higher than for the water pressure method, and therefore it is not the preferred technique. It must be ensured that ducts are able to handle the pressure from winch wires and cables, especially in curves. Similar to the water pressure method, the cables will be pushed into the ducts by a caterpillar. 10. Joint installation Joint pits for normal cross-bonded joints (through link boxes) and joints, which are to be grounded, are shown in the following drawings: 13L L L Joint pits for direct cross-bonded joints are shown in the following drawings: 13L L Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 15/16

16 13L Joint pits for straight joints are shown in the following drawings: 13L L L The drawings also present the location of possible temporary and permanent manholes, the required overlap of the cable ends, and the electrical equipment and connections, which have to be installed in the joint pit. Manholes are defined in drawing 13L It should be noted that for urban applications, Energinet requires rigid joint housings to ensure maximum mechanical stability and durability. 11. Handover testing The cable must at least be tested according to ETS-0082 after the following handovers: 1. Each cable section must be tested, when the individual drums have been delivered from cable manufacturer to Energinet s storage facility. 2. Each cable section must be tested, when the individual drums have been transported from Energinet s storage facility to the actual pulling site. 3. The individual cable length must be tested after the pulling and either just before or just after it is covered with sand. 12. Spare parts Section intentionally left blank; Spare parts specified elsewhere. 13. Documentation Section intentionally left blank; Documentation specified elsewhere. 14. Appendices No appendices. Doc. 13/ EDS-0074 Klassificering: Til arbejdsbrug/restricted 16/16