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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
Electricity Supply
Domain
Electricity Supply - Transmission Networks
Status
Registered
Status date
21 May 2010
Date version published
21 May 2010
Planned review date
31 December 2014
Entry information
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.
Accreditation
Evaluation of documentation and visit by NZQA and
industry.
Standard setting body (SSB)
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.
 New Zealand Qualifications Authority 2016
26014 version 1
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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.
Range
high voltage line earthing, substation earthing, Multiple Earth Neutral (MEN) and
Single Wire Earth Return (SWER).
Performance criteria
1.1
Percentage limits of power system overvoltages are described.
Range
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.
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Element 2
Describe and compare the characteristics of soil types and conditions from at least two
locations.
Range
stratified grounds, measurement of soil resistivity.
Performance criteria
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.
Range
high voltage lines, distribution systems.
Performance criteria
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.
Range
electrode resistance, multiple electrodes, electric shock potential.
Performance criteria
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.
Range
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.
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Element 5
Develop plans for earth mesh and grid designs.
Range
may include but is not limited to – horizontal grids, grounding grids, earth-grids,
electrodes, mesh-mesh, grid-mesh, grid-grid.
Performance criteria
5.1
Sizing of earthing conductors is completed.
Range
5.2
electrical rating, mechanical rating.
Electrodes and jointing methods suitable for the designs are selected.
Range
meshes, grids.
5.3
Electromagnetic forces that could affect the designs are identified.
5.4
Environmental factors are taken into account in the plans.
Range
5.5
corrosion, location, physical protection.
Transient characteristics of earths are taken into account in the plans.
Range
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.
Range
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.
Performance criteria
6.1
Installation of electrodes is described.
Range
manual, mechanical, drilling.
6.2
Desired resistance values are calculated correctly.
6.3
Multiple electrode applications are assessed.
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Element 7
Report on the results of the analysis and conclusion of earth test measurements.
Performance criteria
7.1
Types of instruments used are described.
Range
7.2
Method of measuring resistivity is described.
Range
7.3
ohmmeter, null balance, earth tester, earth loop tester.
Wenner method, fall of potential method.
Field test results are analysed.
Range
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.
 New Zealand Qualifications Authority 2016