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Demonstrate knowledge of mechanical overhead line design
Level
7
Credits
20
Purpose
People credited with this unit standard are able to: identify the properties and
describe the construction of conductors and earthwires, and select different
types for specific duties; calculate conductor sags and tensions; explain
structure spotting and its effects on a mechanical overhead line design; and
complete a design brief for mechanical 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.
Special notes
1
This unit standard is intended for use in engineering courses at graduate level.
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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 content of this unit standard is based on the content of the Queensland
University of Technology unit EEP 217 Overhead Line Design – Mechanical 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
Identify the properties and describe the construction of conductors and earthwires, and
select different types for specific duties.
Range
conductors include – All Aluminium Conductor (AAC), Aluminium Conductor
Steel Reinforced (ACSR), All Aluminium Alloy Conductor (AAAC).
Performance criteria
1.1
The characteristics of the three main types of aluminium conductors are
differentiated.
Range
1.2
Three main types of conductor characteristics are contrasted and compared.
Range
1.3
homogeneous material, composite materials.
The key electrical characteristics of an earthwire are identified.
Range
1.5
at least three examples of – jointing, strength to mass ratio,
resistance, current rating, operating temperature, conductivity.
The Modulus of Elasticity is explained and applied in the selection of
conductors.
Range
1.4
description may include but is not limited to – tension, sag,
composition, voltage
high conductivity material, surge impedance.
The purpose of an earthwire in relation to high voltage lines is explained.
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Element 2
Calculate conductor sags and tensions.
Range
examples include – support heights being equal, support heights differ,
horizontal distance differs, vertical loading at supports, negative weight spans,
temperature variances.
Performance criteria
2.1
Conductor sag is calculated correctly.
2.2
True conductor length is calculated correctly.
2.3
Conductor tension is calculated correctly.
Range
wind loading, ice loading, creep.
2.4
Tangential tension is calculated correctly.
2.5
A tip load calculation is applied.
2.6
Final conductor length is calculated correctly.
2.7
Calculations of sags and tensions are considered and findings are applied to
the design brief.
Range
2.8
a minimum of three of each – single spans, ruling spans
An allowable adjacent span ratio is determined.
Element 3
Explain structure spotting and its effects on a mechanical overhead line design.
Performance criteria
3.1
The principles of structure spotting are explained and applied to a mechanical
overhead line design.
Range
3.2
structure options, structure cost, catenary constant values for
maximum high temperature, catenary constant values for
maximum low temperature, catenary constant values for average
temperature, maximum allowable span, maximum sag hot curve,
wt/wd ratio, negative weight spans, loadings, ruling span
calculation.
Cost of structure spotting per kilometre is calculated.
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3.3
The effects of wind pressure on conductors at structures, and between
structures, is determined.
Range
3.4
swing out on insulators, swing out on spans.
The margin of clearance for swing out mid-span is determined.
Range
33kV, 66kV, 110kV, 220kV.
Element 4
Complete a design brief for mechanical overhead line design.
Performance criteria
4.1
Environmental conditions are determined and how these convert to design
parameters is explained.
Range
4.2
may include but is not limited to – current rating, voltage,
maximum conductor temperature, maximum working wind,
thunder days per annum, maximum and minimum temperatures,
aeolian vibration, ice loading, air pollutants, soil conditions.
Conductor performance is determined, and factors that contribute to and
mitigate against fatigue are appraised.
Range
static stress factors which may include – tension, bending,
clamping stress, residual stress, use of armour rods, use of helical
suspension clamps;
dynamic stress factors which may include – aeolian vibration,
galloping vibration, conductor self-dampening, external dampers.
4.3
Topographical and meteorological conditions that are most likely to contribute to
the cause of aeolian vibration are described.
4.4
An explanation for creep is provided, and expected creep and notate allowable
tolerances are calculated correctly.
Range
explanation to include at least two of – AAC, ACSR, AAAC.
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