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Demonstrate knowledge of mechanical overhead line design

Level / 7
Credits / 20

PurposePeople 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

Special notes

1This unit standard is intended for use in engineering courses at graduate level.

2Performance 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.

3The content of this unit standard is based on the content of the Queensland University of TechnologyunitEEP 217Overhead 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.

Rangeconductors include – All Aluminium Conductor (AAC), Aluminium Conductor Steel Reinforced (ACSR), All Aluminium Alloy Conductor (AAAC).

Performance criteria

1.1The characteristics of the three main types of aluminium conductors are differentiated.

Rangedescription may include but is not limited to – tension, sag, composition, voltage

1.2Three main types of conductor characteristics are contrasted and compared.

Rangeat least three examples of – jointing, strength to mass ratio, resistance, current rating, operating temperature, conductivity.

1.3The Modulus of Elasticity is explained and applied in the selection of conductors.

Rangehomogeneous material, composite materials.

1.4The key electrical characteristics of an earthwire are identified.

Rangehigh conductivity material, surge impedance.

1.5The purpose of an earthwire in relation to high voltage lines is explained.

Element 2

Calculate conductor sags and tensions.

Rangeexamples include – support heights being equal, support heights differ, horizontal distance differs, vertical loading at supports, negative weight spans, temperature variances.

Performance criteria

2.1Conductor sag is calculated correctly.

2.2True conductor length is calculated correctly.

2.3Conductor tension is calculated correctly.

Rangewind loading, ice loading, creep.

2.4Tangential tension is calculated correctly.

2.5A tip load calculation is applied.

2.6Final conductor length is calculated correctly.

2.7Calculations of sags and tensionsare considered and findings are applied to the design brief.

Rangea minimum of three of each – single spans, ruling spans

2.8An allowable adjacent span ratio is determined.

Element 3

Explain structure spotting and its effects on a mechanical overhead line design.

Performance criteria

3.1The principles of structure spotting are explained and applied to a mechanical overhead line design.

Rangestructure 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.

3.2Cost of structure spotting per kilometre is calculated.

3.3The effects of wind pressure on conductors at structures, and between structures, is determined.

Rangeswing out on insulators, swing out on spans.

3.4The margin of clearance for swing out mid-span is determined.

Range33kV, 66kV, 110kV, 220kV.

Element 4

Complete a design brief for mechanical overhead line design.

Performance criteria

4.1Environmental conditions are determined and how these convert to design parameters is explained.

Rangemay 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.

4.2Conductor performance is determined, and factors that contribute to and mitigate against fatigue are appraised.

Rangestatic 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.

4.3Topographical and meteorological conditions that are most likely to contribute to the cause of aeolian vibration are described.

4.4An explanation for creep is provided, and expected creep and notate allowable tolerances are calculated correctly.

Rangeexplanation 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.

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 you wish to suggest changes to the content of this unit standard.

 New Zealand Qualifications Authority 2018