Page 1 of 5 Demonstrate knowledge of the fundamentals of power system earthing Level 7 Credits 15 Purpose People credited with this unit standard are able to: compile an explanation on the purpose of earthing; describe and compare the characteristics of soil types and conditions from at least two locations; compare different types of line design; calculate and compile fault levels and prospective short circuit currents, and describe their effects; develop plans for earth mesh and grid designs; describe installation techniques and materials used for the line project; and report on the results of the analysis and conclusion of earth test measurements. Subfield Domain Status Electricity Supply Electricity Supply - Transmission Networks Registered Status date 21 May 2010 Date version published 21 May 2010 Planned review date 31 December 2014 Entry information Accreditation Standard setting body (SSB) Recommended: one of relevant Bachelor s degree in engineering; National Diploma in Engineering (Electrotechnology) (Level 6) [Ref: 1313]; National Diploma in Engineering (Level 6) with strands in Mechanical Engineering, Production Engineering, and Mechanical Services, and with an optional strand in Practical Endorsement [Ref: 0534]; or New Zealand Certificate of Engineering; or demonstrate equivalent knowledge and skills. Evaluation of documentation and visit by NZQA and industry. Electricity Supply Industry Training organisation Accreditation and Moderation Action Plan (AMAP) reference 0120 This AMAP can be accessed at http://www.nzqa.govt.nz/framework/search/index.do. Special notes 1 This unit standard is intended for use in engineering courses at graduate level.
Page 2 of 5 2 Performance and work practices in relation to the elements and performance criteria must comply with all current legislation, especially the Electricity Act 1992, and any regulations and codes of practice recognised under that statute; the Health and Safety in Employment Act 1992; and the Resource Management Act 1991. Electricity supply industry codes of practice and documented industry procedures include the Safety Manual Electricity Industry (SM-EI) Wellington: Electricity Engineers Association. A full list of current legislation and industry codes is available from the Electricity Supply Industry Training Organisation, PO Box 1245, Hamilton 3240. 3 The following texts may be referenced in conjunction with this unit standard: Tagg, G.F. Earth Resistances (London: Newnes, 1964); Electricity Council of New South Wales, Guide to Protective Earthing (Sydney: The Council, 1992); Dwight, H.B., Calculation of Resistances to Ground (1936), vol 55, AIEE Transactions; Rudenberg, R., Grounding Principles and Practices (1945), vol 64, no 1, Electrical Engineering; Sverak, J.G. et al, Safe Substation Grounding, Part I (1981), vol PAS-100, issue 9, IEEE Transactions; Swan, G. A.H. and McRae, B. P. The Earthing of High Voltage Substations (Electrical Engineering Transactions, The Institution of Engineers Australia, July 1964). 4 The content of this unit standard is based on the content of the Queensland University of Technology unit EEP 201 Fundamentals of Power System Earthing and anyone who has completed and passed that unit is entitled to be awarded this unit standard. Further information about this process may be obtained from the Electricity Supply Industry Training Organisation, PO Box 1245, Hamilton 3240. Elements and performance criteria Element 1 Compile an explanation on the purpose of earthing. high voltage line earthing, substation earthing, Multiple Earth Neutral (MEN) and Single Wire Earth Return (SWER). 1.1 Percentage limits of power system overvoltages are described. power frequency overvoltages, surge voltages. 1.2 Personal safety criteria are described in terms of touch potential. 1.3 Prospective earth fault current levels are stated in explanation. 1.4 Control of earth fault currents is described.
Page 3 of 5 Element 2 Describe and compare the characteristics of soil types and conditions from at least two locations. stratified grounds, measurement of soil resistivity. 2.1 Non-homogenous soils are described. 2.2 Resistivity is explained. 2.3 The soil as a conductor is described. Element 3 Compare different types of line design. high voltage lines, distribution systems. 3.1 Components used on proposed line projects are identified. 3.2 The process of line design is described using flow charts. 3.3 The process of analysing site conditions is described. Element 4 Calculate and compile fault levels and prospective short circuit currents, and describe their effects. electrode resistance, multiple electrodes, electric shock potential. 4.1 Step and touch voltages and potential gradients are derived. 4.2 Current divisions and potential rises of mats and poles are determined by computer-based compilation. computer-based compilation determines earth fault current, line to ground faults (substation end), line to ground faults (mid-line), line to ground faults (at poles). 4.3 Hazardous voltage situations are identified. 4.4 Flow of lightning currents to ground is described. 4.5 Division of earth currents at substations is described.
Page 4 of 5 Element 5 Develop plans for earth mesh and grid designs. may include but is not limited to horizontal grids, grounding grids, earth-grids, electrodes, mesh-mesh, grid-mesh, grid-grid. 5.1 Sizing of earthing conductors is completed. electrical rating, mechanical rating. 5.2 Electrodes and jointing methods suitable for the designs are selected. meshes, grids. 5.3 Electromagnetic forces that could affect the designs are identified. 5.4 Environmental factors are taken into account in the plans. corrosion, location, physical protection. 5.5 Transient characteristics of earths are taken into account in the plans. non-linearity and hysteresis in earths subject to large impulse currents, time-dependent behaviour of distributed earthing systems, effects directly related to high frequency components. Element 6 Describe installation techniques and materials used for the line project. installations may include but are not limited to solid earthing, resistanceearthing, reactance-earthing, arc-suppression (Petersen) coil, earthing and electromagnetic shielding, earthing protection against lightning and electrostatic discharge. 6.1 Installation of electrodes is described. manual, mechanical, drilling. 6.2 Desired resistance values are calculated correctly. 6.3 Multiple electrode applications are assessed.
Page 5 of 5 Element 7 Report on the results of the analysis and conclusion of earth test measurements. 7.1 Types of instruments used are described. ohmmeter, null balance, earth tester, earth loop tester. 7.2 Method of measuring resistivity is described. Wenner method, fall of potential method. 7.3 Field test results are analysed. single electrode, multiple electrodes, MEN systems, soil resistivity. Please note Providers must be accredited by NZQA, or an inter-institutional body with delegated authority for quality assurance, before they can report credits from assessment against unit standards or deliver courses of study leading to that assessment. Industry Training Organisations must be accredited by NZQA before they can register credits from assessment against unit standards. Accredited providers and Industry Training Organisations assessing against unit standards must engage with the moderation system that applies to those standards. Accreditation requirements and an outline of the moderation system that applies to this standard are outlined in the Accreditation and Moderation Action Plan (AMAP). The AMAP also includes useful information about special requirements for organisations wishing to develop education and training programmes, such as minimum qualifications for tutors and assessors, and special resource requirements. Comments on this unit standard Please contact the Electricity Supply Industry Training Organisation info@esito.org.nz if you wish to suggest changes to the content of this unit standard.