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Demonstrate knowledge of electrical overhead line design
Level
7
Credits
20
Purpose
People credited with this unit standard are able to: establish the load factors
that contribute to the design of a transmission line; calculate the insulation
requirements in a transmission line; evaluate the hardware requirements in a
transmission line; develop clearances and maintenance specification in the
transmission line design; determine the protection requirements against
lightning for a transmission line; establish the interferences present in the
design of a transmission line; and complete a design brief for overhead line
design.
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.
 New Zealand Qualifications Authority 2016
26015 version 1
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Special notes
1
This unit standard is intended for use in engineering courses at graduate level.
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 content of this unit standard is based on the content of the Queensland
University of Technology unit EEP 216 Overhead Line Design – Electrical 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
Establish the load factors that contribute to the design of a transmission line.
Range
loads include 33kV, 66kV, 110kV, 220kV.
Performance criteria
1.1
Critical line performance parameters are identified.
Range
1.2
The prevailing climatic conditions are analysed and impact calculated correctly.
Range
1.3
maximum temperature, relative humidity and height above sea
level, thunder-day levels, wind speed, direction, wind span.
Line environment is identified and analysed.
Range
1.4
structural security, lightning performance, maintenance,
electromagnetic fields, audible noise limit, unbalance limit.
footing resistance, pollution.
Voltage stress is calculated correctly.
Range
continuous 50Hz voltage, temporary overvoltages, slow-front
voltages, fast-front overvoltages, combined voltages.
 New Zealand Qualifications Authority 2016
26015 version 1
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Element 2
Calculate the insulation requirements in a transmission line.
Range
types of insulator include - disc, long rods, line posts, horizontal vee.
Performance criteria
2.1
The different types of insulation material and their use to meet insulation
conditions are compared.
Range
2.2
Insulation stress is calculated correctly.
Range
2.3
glass, porcelain, composite.
continuous 50Hz voltage, temporary overvoltages, slow-front
voltages, fast-front overvoltages, combined voltages.
The effects of atmospheric conditions on insulation strength are determined.
Range
material fatigue, corrosion, stress.
2.4
Insulation distances and approach distances for a given design of a
transmission line are specified.
2.5
Compression fitting is calculated correctly for the insulators selected for the
design.
2.6
Switching surge currents and power frequency voltages are calculated and the
appropriate circuits designed.
Range
continuous 50Hz voltage, temporary overvoltages, slow-front
voltages, fast-front overvoltages, combined voltages.
Element 3
Evaluate the hardware requirements in a transmission line.
Performance criteria
3.1
Line cost components are identified.
3.2
Construction and energising costs of the transmission lines are calculated
correctly.
Range
3.3
single circuit, double circuit, single pole, steel towers.
The effects of wind pressure on conductors at structures and between
structures are determined.
Range
swing out on insulators, swing out on spans.
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3.4
The margin of clearance for swing out mid span is determined.
Range
33kV, 66kV, 110kV, 220kV.
Element 4
Develop clearances and maintenance specification in the transmission line design.
Performance criteria
4.1
The insulator swing out is determined.
Range
4.2
impulse clearance, maintenance clearance, power frequency
clearance, live line clearance.
The various clearances for a transmission line are determined.
Range
power frequency, switching surge, phase-to-phase tower, intraspan clearances.
4.3
The maintenance approach and live line clearances are calculated correctly.
4.4
Maintenance factors for the transmission line design are determined.
Range
conductors and earthwires, insulators, electrical clearances,
climbing aids, earthing and bonding, corrosion, time intervals.
Element 5
Determine the protection requirements against lightning for a transmission line.
Performance criteria
5.1
Earthing and protection systems are compared.
Range
5.2
circuit outages, single earthwires, double earthwires.
Shielding requirements are calculated correctly and designed.
Range
earthwire effective shielding angle for 220kV line with 13 normal
disc for insulation strings.
5.3
Ground flash density of lightning strikes is identified and accounted for.
5.4
Lightning performance is calculated correctly.
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Element 6
Establish the interferences present in the design of a transmission line.
Performance criteria
6.1
Areas of noise are identified.
Range
audible noise, radio and television noise (sound static and picture
interference), insulation corona.
6.2
Corona discharges are explained.
6.3
The corona onset surface voltage gradient is calculated using Peek’s equation.
6.4
Electric and magnetic fields are identified.
Range
Coulomb’s Law, Ampere’s Theorem.
Element 7
Complete a design brief for electrical overhead line design.
Performance criteria
7.1
A suitable structure selection is proposed with specific criteria.
Range
environmental, terrain, aesthetic, climatic rating, operational
requirements.
7.2
The failure possibilities are determined.
7.3
Line parameters and operating conditions are specified.
Range
computation for – insulation requirements, system voltages,
clearances, system fault levels.
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.
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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