clearances and conductor spacings

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Clearances andconductor spacings and a safe access for a.c.switchyards

T R A N S P O W E R APPROVED S T A N D A R D

Implementation date: March 2009

C O P Y R I G H T 2 0 0 9 T R A N S P O W E R N E W Z E A L A N D L I M I T E D . A L L R I G H T S R E S E R V E D .

This document is protected by copyright vested in Transpower New Zealand Limited (Transpower). No part of the document may bereproduced or transmitted in any form by any means including, without limitation, electronic, photocopying, recording or otherwise, withoutthe prior written permission of Transpower. No information embodied in the documents which is not already in the public domain shall becommunicated in any manner whatsoever to any third party without the prior written consent of Transpower.

Any breach of the above obligations may be restrained by legal proceedings seeking remedies including injunctions, damages and costs.


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PREFACE

Issue 3 of this standard is a major revision of the previous Issue 2. It has been re-developed to:

1. Include clearances and spacings for 400 kV a.c. switchyards.

2. Improve safety by requiring minimum maintenance access clearances to enable the use ofmobile elevated work platforms (MEWPs) in order to reduce fall hazards.

3. Improve safety by requiring work plane heights to be aligned with the New ZealandDepartment of Labour Code of Practice for Manual Handling (the design principles for manualhandling are identical to those considered for determining work platform heights).

4. Improve safety by up-dating minimum height to live metal clearances to improve access tocircuit breaker mechanism boxes, and to prohibit designs based on the use of steps for thispurpose as per Service Advisory TP.DS 62.01 SA1 (now superseded by this document).

5. Improve safety by re-instating a minimum height requirement to the lowest insulating shed oninsulating support columns.

6. Improve safety by requiring existing installations that do not comply with minimum clearancesas determined by national and international standards to be remedied by restricting access anduse of warning signs.

7. Improve circuit availability by requiring that routine maintenance and equipment change-outscan be carried without necessitating the shutdown of nearby energised circuits.

8. Include design criteria for extending and modifying existing a.c. switchyard structures.

9. Alignment with Australian practices except when this would involve conflict with IECstandards. The range of terms used has been significantly increased and these are defined inAppendix ADefinitions.

Because of the extensive nature of the changes in this third issue of TP.DS 62.01 the Revision Historylog has been reset to restart again as at the date of issue.

Keywords

clearances maintenance groups, zones,and access

mobile elevating workplatforms (MEWPs)

protective barriers andobstacles

provision for inadvertentmovement (Di)

spacings

walking access clearance (W)

2009 - Transpower New Zealand Limited 2


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Revision History

C O N T A C T

This document is the responsibility of Engineering Services Group,Transpower New Zealand Limited, Wellington. If you have anyqueries please contact the Engineering Services Manager.

If you would like to make suggestions to improve this document,please use the Controlled Document Feedback Form located at therear of this document or online via the Controlled Documentationhomepage of the Transpower website at www.transpower.co.nz

C O N F I D E N T I A L I T Y

All information disclosed in this document that is not general publicknowledge must be treated as strictly confidential and may not beused or disclosed except for the purpose of developing documentationfor the benefit of Transpower.

L I M I T A T I O N O F L I A B I L I T Y A N D

D I S C L A I M E R O F W A R R A N T Y

Transpower New Zealand Limited makes no representation orwarranties with respect to the accuracy or completeness of theinformation contained in the document. Unless it is not lawfullypermitted to do so, Transpower specifically disclaims any impliedwarranties of merchantability or fitness for any particular purpose

and shall in no event be liable for, any loss of profit or any othercommercial damage, including, but not limited to, special,incidental, consequential or other damages.

M I N I M U M R E Q U I R E M E N T S

The requirements set out in Transpowers standards are minimumrequirements that must be complied with by contractors, includingdesigners and other consultants. The contractor is expected toimplement any practices which may not be stated but which canreasonably be regarded as good practices relevant to the purpose ofthis standard. Transpower expects contractors to improve upon theseminimum requirements where possible and to integrate theseimprovements into their procedures and quality assurance plans.

Date Issue Amendments

Feb 2009 3 Refer to Preface on page 2.

http://www.transpower.co.nz/http://www.transpower.co.nz/http://www.transpower.co.nz/


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CONTENTS

PREFACE............................................................................................................................21 PURPOSE............................................................................................................................52 POLICY................................................................................................................................53 COMPLIANCE.....................................................................................................................54 REFERENCES AND BACKGROUND MATERIAL ............................................................65 GENERAL REQUIREMENTS .............................................................................................7

5.1 Design Drawings.................................................................................................................75.2 Continuity in Service ........................................................... ...............................................75.3 Design Co-ordination ........................................................... ..............................................75.4 Tables ................................................................ ................................................................ ....8

6 BASIC ELECTRICAL CLEARANCES............................................................................. 116.1 Requirements .................................................................... .................................................116.2 Basic Electrical Clearances ...................................................................... .........................116.3 Increased Minimum Clearances Under Special Conditions .......................................116.4 Reduced Minimum Clearances Under Special Conditions.........................................11

7 CLEARANCES FOR SAFE ACCESS AND CONDUCTOR SPACINGS........................ 127.1 Fundamental Design Requirement for Safety...............................................................127.2 Walking Access Clearances..............................................................................................137.3 Minimum conductor heights ................................................................ ...........................147.4 Access for maintenance work..........................................................................................157.5 Busbar Heights and Spacings ................................................................. .........................237.6 Standard Clearances & Conductor Spacings.................................................................247.7 Alternative Clearances & Conductor Spacings.............................................................247.8 Low level equipment installations/ protective barriers (capacitors etc.)..................267.9 Access for Maintenance Vehicles and Plant ..................................................................277.10 Security Fence Clearances................................................................................................337.11 Safe Access to Operational Equipment ..................................................................... .....33

8 EXISTING A.C. SWITCHYARDS..................................................................................... 368.1 Policy requirements ................................................................... .......................................368.2 Requirements for ground clearances and busbar heights ...........................................368.3 Non-compliant existing structures .................................................................. ...............368.4 Modifications or extensions.............................................................................................38

9 IMPULSE TESTED EQUIPMENT .................................................................................... 399.1 Transformers......................................................................................................................39

APPENDICES

A DEFINITIONS ................................................................................................................... 40B CONTROLLED DOCUMENT FEEDBACK FORM .......................................................... 42


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1 PURPOSE

This standard defines minimum clearances to protect personnel, vehicles and equipmentagainst inadvertent contact, or hazardous proximity, to exposed conductors, and defines the

minimum basic clearances required in a.c. switchyards.

2 POLICY

All existing and new a.c. switchyards shall comply with New Zealand legalrequirements and the requirements of international and national standards, and NewZealand industry documents as set out in Section 3, Compliance.

New a.c. switchyards shall be designed so that the required continuity in service ofenergised equipment is maintained when nearby equipment is either maintained, orreplaced.

New a.c. switchyard layouts shall facilitate safe and efficient access by competent

employees who are carrying out operations and maintenance work using mobileelevated work platforms where required. Where practical access for MEWPs shallalso apply to modifications and extensions to existing a.c. switchyards.

3 COMPLIANCE

The design of Transpower a.c. switchyards shall meet the minimum clearance requirementsof the following documents:

1. IEC 61936-1 Power installations exceeding 1 kV a.c. Common rules

2. NZECP 34 New Zealand Code of Practice for Electrical Safe Distances

3. AS 2067 High voltage installations and ESAA NENS 04 National guidelines for safe

approach distances to electrical apparatus

4. IEC 60071-2 Insulation co-ordination Part 2:Application guide

5. IEC 60076-3 Power transformers Part 3: Insulation levels, dielectric tests and externalclearances in air

Where conflict exists between the above documents they shall take precedence in the orderlisted.

The design of Transpower a.c. switchyards shall facilitate compliance with the followingdocuments:

Electricity Regulations 1997

Regulations made under the HSE Act 1992

Safety Manual Electricity Industry (SM-EI)

Code of Practice for Manual Handling, Department of Labour documents

Existing a.c. switchyards that do not fully comply shall be brought into line with therequirements of Section 8Existing a.c. switchyards.


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4 REFERENCES AND BACKGROUND MATERIAL

The following documents are referred to in this standard or provided background materialfor the development of this standard:

TP.DG 01.01 Insulation co-ordination

TP.DG 30.01 Electric and magnetic field design parameters for a.c. 50 Hz transmissionlines, substations and underground, cables

TP.DG 47.01 Safety by design strategy and application: elimination of hazards forpeople, plant and the environment during construction, operations,maintenance and disposal

TP.DS 53.02 Station security physical and electronic requirements

DC 3.1.2:1974 Electrical design standard

AS 2067 High voltage installations

BS 7354 Code of practice for design of high voltage open-terminal stations

ESAA NENS 04 National guidelines for safe approach distances to electrical apparatus

ICNIRP International Commission on Non-ionizing Radiation ProtectionGuidelines: Guidelines for limiting exposure to time-varying (1998)electric, magnetic and electromagnetic fields

IEC 60071-2 Insulation co-ordination Part 2:Application guide

IEC 60076-3 Power transformers Part 3: Insulation levels, dielectric tests andexternal clearances in air

IEC 61936-1 Power installations exceeding 1 kV a.c. Common rules

IEEE 979 Guide for substation fire protection

NZECP 34 Electrical Safe Distances

SM-EI Safety Manual Electricity Industry

Electricity Regulations Electricity Regulations 1997

Code of Practice forManual Handling

New Zealand Department of Labour Code

HSE Act Health and Safety in Employment Act 1992


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5 GENERAL REQUIREMENTS

5.1 Design drawings

Design drawings for all new a.c. switchyards, and extensions, or modifications to existinga.c. switchyards shall be prepared by the designer and submitted to Transpower forapproval. These drawings shall include critical dimensions and show:

1. The proposed equipment maintenance groups.

2. The proposed equipment maintenance zones.

3. The type of temporary access equipment that can be used for routine maintenanceand the replacement of equipment.

4. Clearances and minimum spacings.

5. Access ways for routine maintenance/ equipment change-outs.

Refer to the drawing series TP58394 for examples of points 1 to 5 above.

5.2 Continuity in service

5.2.1 Routine maintenanceAll a.c. switchyards shall be designed so that routine maintenance can be safely carried outwithout the need to remove from service, nearby energized equipment in other circuits.

Note that during replacement, upgrade or extension projects existing equipment within theassociated maintenance group that does not meet this requirement shall, where practicable,be relocated to a position that does meet this requirement.

5.2.2 Equipment replacement

5.2.2.1 Network security requirements

Circuits shall be designed so that equipment can be safely replaced without the need toremove from service nearby energized equipment in other circuits.

5.2.2.2 Zero contingency circuits

Where there is no back-up for circuits connected to a busbar (i.e. there is only n security), anew circuit connected to that busbar shall be designed so that circuit breakers can be safelyreplaced without the need to remove from service, either the busbar or nearby circuits.

5.2.2.3 Bus coupler installations

Bus coupler installations shall be designed so that equipment can be safely replaced withoutthe need to remove from service, nearby energized equipment in other circuits, includingsections of bus.

Example: To be able to replace the bus coupler circuit breaker and CTs with both adjacentbusbars live.

5.3 Design co-ordination

5.3.1 Switchyard layout and patterningReplicable layouts that can be readily related to the single line diagram shall be used. Theequipment layouts and conductor dispositions in circuit bays of the same type (line,transformers, capacitor banks etc.) shall consistently conform to an established pattern.

5.3.2 Electric and magnetic fieldsClose proximity to high voltage conductors can result in unacceptable exposure to electric

and magnetic fields.



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Internal fences around air-cooled reactors and other areas of high magnetic fields shallprotect personnel outside the fence from magnetic fields in excess of the ICNIRP guidelinefor occupational exposure.

TP.DG 30.01Electric and magnetic field design parameters for a.c. 50 Hz transmission lines,

substations and underground, cables provides more specific requirements with regard to theconsideration of the limitation of EMF exposures during design.

5.4 Tables

Table 1: Minimum clearancesfor voltage range I: 1 kV < Um up to and including 245 kV

Nominal systemvoltage

Un

Highest equipmentvoltage

Um

LIWV1

Minimum phase to earth (N) &phase to phase clearance

(kV) (kV) (kVpk) (mm)

11 12 75 500 (150 see Note 2)

22 24 125 500 (220 see Note 2)

33 36 170 500 (320 see Note 2)

50 55 250 500

66 72.5 325 630

110 123 550 1100 (see Note 3)

220 245 1050 2100 (see Note 4)

Notes:1 Clearances are determined by LIWV not by nominal system or highest equipment voltages.2 Reduced clearances may be used if there is no practical alternative, if other means are

provided to prevent flashovers by birds or vermin. The reduced clearances are not to beused to calculate maintenance clearances, protective barrier/obstacle clearances, or securityfence clearances.

3 110 kV lines which have a LIWV of 450 kVpk have a corresponding minimum clearance of900 mm.

4 220 kV lines and transformers which have a LIWV of 950 kVpk (or 900 kVpk fortransformers prior to about 1982) have a corresponding minimum clearance of 1900 mm.



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Table 2: Minimum clearances for voltage range II: Um > 245 kV

Nominalsystemvoltage

Un

Highestequipment

voltage

Um

RatedLIWV

RatedSIWV

Minimumphase to

earth

clearanceN

SIWV Minimum phase-to-phaseclearance

(V) (kV) (kVpk) (kVpk) (mm) (kVpk) (mm)

400 420 1425 1050 3400 1575 4200

Note: The nearest IEC 61936-1 Nominal system voltage to 400 kV is 380 kV. Transpower hasselected a nominal system voltage of 400 kV. As the nominal system voltage is defined as asuitable approximate value 400 kV is used in Table 2 as opposed to 380 kV.

Table 3: Standard clearances for safe access and conductor spacings A.C. voltagesfrom August 2008

Nominalsystemvoltage

Un

Minimumheight of liveparts above

fixedaccessiblesurfaces

1, 2

W

Minimumbusbar

(rigid type/no sag)

clearanceheight

1

Busbarspacing

centre line tocentre line forrigid busbars

Minimumvertical

work safetyclearance

1,3

V (includesDiV of

1000 mm)

Minimumhorizontal worksafety clearance

1,3H (includes DiH

of 1900 mm andMa of 1900 mm)

(kV) (mm) (mm) (mm) (mm) (mm)

66 3070 4070 1500 3070 4430

110 3540 4540 2100 3540 4900

220 4540 5540 3600 4540 5900

400 5840 6840 5400 5840 7200

Notes:1. All clearances are surface to surface taut string distances, whereas conductor spacings are centre

line to centre line measurements.2. Refer to Figure 3 for installation example designed to achieve walking access clearance W.3. The maintenance clearances H and V are based on the use of MEWPs as illustrated in

Figure 9.4. Because outdoor 33 kV and lower voltage level air insulated a.c. switchyards are no longer

economic due to the comparatively low cost of indoor switchgear installations these are notincluded in the above table.

5. Because the trend is to phase out 50 kV lines and a.c. switchyards these are not included in theabove table. Therefore for 50 kV installations design to 66 kV clearances.



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Table 4: Revised safety distances as from 20th April 2005 to July 2008

Nominal system voltage

Un

Minimum height of live partsabove fixed accessible

surfaces

Minimum busbar (rigid type/no sag) clearance heightassuming vehicle access

(kV) (mm) (mm)

11 3000 4000

22 3000 4000

33 3000 4000

50 3000 4000

66 3100 4100

110 3500 4500

220 4500 5500

Refer to Section 8.

Table 5: Acceptable safety distances for installations built prior to 20th April 2005

Nominal system voltage

Un

Minimum height of live partsabove fixed accessible

surfaces

Minimum busbar (rigid type/no sag) clearance heightassuming vehicle access

(kV) (mm) (mm)

11 2600 3600

22 2700 3700

33 2800 3800

50 2900 3900

66 3100 4100

110 3500 4500

220 4500 5500

Refer to Section 8.


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6 BASIC ELECTRICAL CLEARANCES

6.1 Requirements

The requirements of this section apply to both new and existing a.c. switchyards.

Insulation coordination of electrical equipment is required to provide a level of protectionfor personnel and equipment by reducing flashovers caused by system over-voltages andlightning strikes. Basic electrical clearances are required in order to achieve this purpose.

6.2 Basic electrical clearances

Tables 1 and 2 list Transpower nominal system voltages, highest equipment voltages,lightning impulse withstand voltage (LIWV) and corresponding minimum phase to earthclearances (N) and phase to phase clearances. These clearances are used for a.c.switchyard structures, conductors, and insulators etc. that, for practical reasons, have notbeen tested for compliance with the LIWV type tests, either individually or as a total builtunit. The clearances are based on conservative criteria and are to be used for any outdoor

equipment that has not passed the appropriate LIWV type test. Circumstances whenincreased clearances are, or may be required, are detailed in subsection 6.3.

6.3 Increased minimum clearances under special conditions

Circumstances when the minimum clearances given in Tables 1 and 2 shall be or mayrequire to be increased are as follows:

(a) Minimum clearances between conductors of an installation that may be subject tophase opposition shall be 20 % higher than the standard minimum values.

(b) Minimum clearances between conductors of an installation, which are assigned todifferent insulation levels, shall be 25 % higher than the standard minimum valuesestablished for the higher insulation level present.

(c) Where conductors can move under the influence of short circuit forces, at least 50 %of the standard minimum clearances shall be maintained as a minimum.

(d) Where conductors can move under the influence of wind, at least 75 % of the standardminimum clearances shall be maintained as a minimum.

6.4 Reduced minimum clearances under special conditions

In cases where there is insufficient space available to achieve the minimum clearances then,subject to approval by Transpower, reduced clearances may be used provided that suitablemeasures are put in place such as barriers or obstacles to ensure the protection of personnel,and provided the achieved probability of flashover is controlled to a level acceptable toTranspower.



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7 CLEARANCES FOR SAFE ACCESS AND CONDUCTOR SPACINGS

This section sets out the minimum clearances required for safe access to a.c. switchyards,and also includes the minimum conductor spacingrequirements for new a.c. switchyards.

7.1 Fundamental design requirement for safety

Designs must ensure that competent personnel can carry out operating and maintenanceprocedures without inadvertently encroaching within the danger zone.

The danger zone is defined by the minimum phase to earth clearance (N) to liveconductors.

Figure 1: Danger zone concept



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7.2 Walking access clearances

New a.c. switchyards shall be designed to have minimum safe clearances from all surfacesthat are accessible to competent employees walking throughout the substation.

Figure 2: Minimum design dimensions for safe access



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The minimum walking access clearance to live parts from accessible ground, or accessibleplatforms shall be W, where W = N + RV and RV = 2440 mm.

7.3 Minimum conductor heights

(a)

The minimum conductor height shall not be less than the greater of the minimumheight of live conductors above fixed accessible surfaces given in Table 3 or thewalking access clearance W, where W= N + 2440. The clearance W is referenced tothe maximum conductor sag.

(b) The lowest part of any insulation, for example the upper edge of metallic insulatorbases, shall not be less than 2440 mm above the accessible surface.

Figure 3: Minimum design dimensions for walking access

Note, as in the case of capacitor voltage transformers, attention to detail is required since thelowest live conductor is not always located at the equipment terminals.



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7.4 Access for maintenance work

New a.c. switchyard designs shall be based on the provision of safe and efficientmaintenance access from temporary elevated surfaces for all work that cannot be done fromground level.

It shall be possible to locate temporary work platforms so that routine maintenance can becarried out without the need for outages of equipment in other equipment maintenancegroups.

Standard designs shall not be based on the use of scaffolding/ climbing /ladders for routinemaintenance access. The exceptions to this are:

1. Ladders for inspection purposes.

2. Scaffolding which may be necessary due to the unique nature of the work, such as re-termination of high voltage power cables.

The preferred means of access for maintenance work is a MEWP.

Junction boxes shall not be located such that they impede the positioning of temporary workplatforms. For example, equipment should not be located in the area in front of a circuitbreaker, or the area along the side adjacent to the access route for maintenance plant.

It shall be possible to maintain equipment such as boundary fences, spare transformer unitsetc. without requiring shutdown of any primary electrical equipment.

7.4.1 Equipment maintenance access groupsEquipment maintenance groups are formed by splitting the equipment into logical groups,any of which can be removed from service as a group for routine maintenance andinspection. A typical example of this is indicated in Figure 4.



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Figure 4: SLD primary equipment maintenance groups

7.4.2 Equipment maintenance zonesMaintenance zones are based upon the maintenance access width, the volume occupied bythe equipment, and the work plane heights. Refer to Figures 5, 6 and 7 below.



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Figure 5: CB/CT maintenance access envelope and zone plan view

The required height of the temporary work platform is determined by the highest workplane height. Generally, the highest work plane shall be at the same height as the highestequipment point, and for ergonomic reasons, is taken as being located 1000 mm above thework platform.

For circuit breakers the highest work plane shall be at the same height as the highestterminals, and taken as being located 1000 mm above the work platform for ergonomic

reasons.



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Figure 6: Maintenance access envelope and zone vertical view

A maintenance access width plus sufficient room to facilitate replacement of majorcomponents, as well as replacement of the entire unit of equipment, shall be providedaround the periphery of all large equipment items such as transformers.



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Figure 7: Transformer maintenance access

It may not always be practical to provide an access width along each side of an item ofequipment in order to meet general requirements.

The maintenance access series of drawings TP58394 (refer subsection 5.1 above) is beingextended to show maintenance access arrangements as they become available for varioustypes of equipment.

7.4.3 Positioning of temporary elevated work platformsTemporary elevated work platforms shall be able to be safely moved into the work positionwithout requiring outages of equipment other than the equipment to be worked on. Thecomponent distances in Figures 8 and 9 have been selected to cater for a reasonably wide

range of MEWPs as used by contractors.



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Figure 8: Mobile elevating work platforms minimum design requirements



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7.4.4 Work Position of Temporary Elevated Work PlatformsOnce in position the required minimum clearances are as per Figure 9 below.

Figure 9: Boom type EWPs heights and clearances



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7.4.5 Access using laddersWhere it is not possible to gain access using MEWPs, then access using ladders ispermissible for inspection purposes, but ladders are not to be used as work platforms.

Figure 10: Use of ladders heights and clearances



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7.4.6 Work safety clearances formulaFor definitions of Di, (including DiV and DiH), Rv, andRh, refer to the distance forinadvertent movement, vertical reachand horizontal reach respectively in the definitionssection.

(a) The vertical work safety clearance, V = N + DiV + Rv Work plane height, where:

Vertical reach (Rv) = 2440 mm

Work plane height = 1000 mm

(b) The horizontal work safety clearance, H = N + Ma + DiH

Di values to be used:

MEWP boom or stick type 1000 mm for DiV and 1900 mm for DiH

Scissor lift platform 1000 mm for DiV and 1500 mm for DiH

Ladder 300 mm for DiV (allows for one step) and 0 m forDiH

Vehicle, or mobile plant in transit (subsection 7.9) 1000 mm for DiH, and 0 mm for DiV

All other applications, unless the type ofequipment justifies the use of a value of Di

0 mm

Ma values to be used:

MEWP boom or stick type 1900 mmScissor lift platform 1900 mm

Ladder 25 % of working length of ladder (mm)

Security fence spacing (subsection 7.10) 1000 mm

Protective barriers and obstacles 1000 mm

All other applications 1000 mm

7.5 Busbar heights and spacings

7.5.1 Busbar mounting heightsGenerally busbar mounting heights are to comply with Table 3 to allow vehicles and plantto pass underneath. The required height is to the lowest part of the busbar. For verticallyspaced busbars the required height is the height to the lowest part of the lowest busbar.

Mounting heights for flexible busbars and other sections of live conductor shall be designedsuch that under the worst combination of conditions the minimum height at any point shallnot be less than that required by Table 3.

Busbars mounted in a special enclosure, which prevents access to personnel while theequipment is live, may be mounted at any height sufficient to give phase to earth clearancesin accordance with Table 1 and 2. In such cases protective barriers shall be installed inaccordance with subsection 7.8.



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7.5.2 Busbar horizontal spacingsThe centre line to centre line spacings in Table 3 allow for the installation of the typicaldesigns of disconnectors and earth switches in line with the busbars. The typicaldisconnectors are rocking and vertical break types at 33 kV and vertical break at 72.5 kV,

123 kV and 245 kV. Centre rotating disconnectors and some centre break are alsoaccommodated at 72.5 kV, 123 kV and 245 kV. For single side break disconnectors thespacings must be increased.

The spacings are also suitable for in-line installation of current transformers and circuitbreakers.

Vertically-spaced busbars must meet the requirements of Table 1 and 2, after making dueallowance for flexibility, etc.

Flexible or strung busbars require greater spacings to allow for side swing and theseparation of bundled conductors.

7.6 Standard clearances and conductor spacings

Table 3 summarizes the above subsections and gives the minimum vertical and horizontalwork safety clearances (V and H) for new a.c. switchyards.

7.7 Alternative clearances and conductor spacings

Alternatives to the above standard clearances and conductor spacings may be proposed toTranspower provided they meet the policy requirements, and meet:

1. The walking access and minimum equipment height requirements as set out inTable 3 above.

2. The maintenance clearances formulae and values as set out above.

The selection of alternative options is to be based on the following hierarchy:

3. Use of boom or stick type elevating work platforms as set out above.

4. Use of other types, e.g. scissor type MEWPs.

5. Other options.

Drawings of the proposed alternative shall be submitted to Transpower for approval by theManager responsible for this standard and approval of the manager responsible forequipment maintenance.



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7.7.1 Scissors elevating work platforms

Figure 11: Scissor lifts heights and clearances fall back option 1

Where the provisions of this Standard cannot be practicably achieved, the designer maypropose an alternative solution for Transpowers consideration, or request advice from

Transpower on alternative acceptable solutions. For example, in the case of scissor type



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MEWPs a value of Ma less than 1900 mm may be proposed if suitable narrower mobileequipment would suit the work.

7.8 Low level equipment installations/ protective barriers (capacitors etc.)

Where necessary the designs shall incorporate earthed protective barriers, and/or protectiveobstacles and appropriate warning signage to ensure that competent employees can walksafely as intended and gain access where necessary throughout the substation.

Figure 12: Protection against direct contact

Protective barriers shall be of substantial construction and shall be suitable for the

environment in which they are located. They shall limit the approach of personnel carryingout routine inspections, operations or maintenance to a safe distance from the live parts.



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Either solid or mesh barriers shall be used as per Figure 12. Barriers with openingsexceeding 50 mm shall not be used.

For non-rigid protective barriers and wire meshes, the clearance values shall be increased totake into account movement or deflection of the protective barrier or mesh and meet the

worst case seismic and wind design loads.

7.9 Access for maintenance vehicles and plant

7.9.1 ClearancesThe access envelopes designed for maintenance vehicles and plant shall include provisionfor inadvertent movement, provision for door opening, and shall have a clearance fromoverhead conductors and other live parts, equal to, or greater than the reduced minimumapproach distance given in NZECP 34 Table 6 plus 100 mm. (Refer to Figures below).

7.9.2 Under station busbarsMounting heights for flexible busbars and other sections of live conductor under whichvehicles may pass shall be designed such that under the worst combination of conditions the

minimumheight at any point shall not be less than that given in Table 3. This is for thepassage of maintenance equipment underneath busbars on the basis that such equipmentmovements are carried out in accordance with SM-EI Rule 3.712.

Busbars mounted in a special enclosure, to which access by personnel is prevented while theequipment is live, may be mounted at any height sufficient to give phase to earth clearancesin accordance with Tables 1 and 2.

7.9.3 Primary equipment excluding transformersTo ensure equipment maintenance and replacement of typical bay equipment such as CBs,CTs etc. can be undertaken safely and efficiently, access routes shall be provided that meetthe following criteria:

1. As a minimum straight through access shall be available between every seconddiameter from one side of the structure to the other.

2. The access route and area provided shall be suitable for the following MEWPs andcrane:

(a) Genie Z-45/ 25J RT

(b) Genie S-45

(c) Franna AT-20 (20 tonne crane, required clearance height 3100 mm).

The minimum turning radii shall be based on the largest specified turning radii of thesetypes plus 1000 mm.

3. In combination with the maintenance zones and available area enable equipment

change-outs to be carried out safely and efficiently.

4. Meet the minimum access route profile requirements as indicated in the figuresbelow.

Note, the above crane and MEWPs have been selected solely for the purpose of ensuringthat design access envelopes cater for a reasonable range of mobile plant that themaintenance contractors may need to use for typical bay equipment.

7.9.4 Transformer or heavy item accessFormed heavy transport routes shall be provided for the installation and removal oftransformers or other heavy items.

Access routes for transformer transporters and cranes intended for lifting transformers shall

meet the requirements of Figures 13 to 16 except that the vehicle envelope shall have aminimum width of 3000 mm and a minimum height of 4500 mm. Actual transformer



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dimensions, and lifting arrangements etc. should be specified during the design phase, andappropriate increases in height/ width made to the vehicle envelope as necessary.

Corners for the transport route shall have an outside radius of not less than 10,000 mm. Anappropriate increase in turning radius shall be used where it is foreseen that required

turning radius could exceed 10,000 mm.

The transport route shall provide for a minimum loaded vehicle clearance to live conductorsof RMAD + 100 mm.

Equipment shall be located so that no outages are required during movement of thetransporter with or without the transformer loaded.

If the required space for access is not possible because of site restrictions, warning signsshall be attached to structures at a height of approximately 2,400 mm to their underside andstop lines shall be painted across the access route.

7.9.5 Equipment mounted on high structuresSafe access for MEWPs having sufficient reach shall be provided for work on equipment

items such as light fittings, lightning spires etc. without the need to remove primaryequipment from service. For example in some cases a high reaching type MEWP such as aGenie S-65 may be required.

7.9.6 Calibration vehicle and trailer accessAt sites where revenue metering is carried out at voltages above 33 kV, access shall beprovided for the calibration vehicle and trailer to be safely parked within 4,000 mm of theinstrument transformers that require calibration.



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Figure 13: Vehicle access between non-live equipment



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Figure 14: Vehicle access between de-energised bay and live bay



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Figure 15: Vehicle access between live bays



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7.9.7 Vehicle & plant access around structure perimetersWherever practicable, a vehicle access route shall be provided all the way around the insideof the substation security fence of minimum dimension as per Figure 16 below.

Figure 16: Vehicle access around inside of security fence

Corners of access routes around structure perimeters shall, where practical, have an outside

radius of not less than 10,000 mm.



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7.9.8 Stable access and work surface for MEWPs and crane

A stable durable surface that is capable of carrying a fully loaded MEWP of any of the typeslisted in clause 7.9.3 shall be provided for maintenance access/ equipment change outs:

Genie Z-45/ 25J RT

Genie S-45

The surface layer properties shall be such that:

(a) Significant damage does not occur to the surface, and that

(b) Unforeseen movement of the MEWP does not occur when the MEWP is fully loadedand turning/ slewing, or when a crane is lifting an equipment item such as a circuitbreaker onto a transport truck.

7.10 Security fence clearances

The clearances/ distance between switchyard perimeter security fences and equipment shallcomply with the minimum requirements of Figure 16. Where this is not possible the

minimum security fence clearances shall be based on one of the following alternatives:

(a) N + 1000 mm, when boundary fence is a solid wall;

(b) N + 1500 mm, when boundary fence is mesh/ with openings construction.

For alternatives (a) and (b) the fence must be of a low maintenance type to minimiseequipment outages for maintenance work.

For maintenance purposes the top of the security fence is to be treated as a work plane, andthe overhead live conductor limit designed to be no less than V (refer to Figure 16).

Vertically above and beyond the outside of the security fence the provisions of NZECP 34apply with regard to vertical height of the conductor above the ground and the top of thefence.

7.11 Safe access to operational equipment

7.11.1 Equipment mechanism boxesSafe access from an accessible surface (normally at ground level) shall be provided foroperational or in-service inspection purposes of equipment mechanisms, counters, gauges,mechanism boxes etc.



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Figure 17: Live tank CB installation



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7.11.2 Safe access to equipment at 50 kV and lower voltage level

Figure 18: 33 kV / 415 kV local service transformer (new installation)



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8 EXISTING A.C. SWITCHYARDS

8.1 Policy requirements

Existing a.c. switchyards shall meet the policy compliance requirements set out in Section 3,in order to ensure a consistency of approach to safety.

8.2 Requirements for ground clearances and busbar heights

The minimum heights of live metal/conductors above ground for walking access and forvehicle access under busbars, as scheduled in Tables 4 and 5 in subsection 5.4, apply toexisting structures. The clearances and heights in Table 4 apply to structures designed after20th April 2005 to July 2008, while those in Table 5 apply to structures designed before 20thApril 2005.

Tables 4 and 5 give the height above normally accessible ground for access within a fencedstructure area, in which live metal other than busbars, i.e. not exceeding 1 m in anyhorizontal dimension, may be mounted. This permits some flexibility to cater for different

arrangements of the connections between equipment terminals and overhead busbars, butthe transition to the busbar height should be made as close as reasonably possible to theequipment terminals. Ideally vertical droppers onto the equipment terminals would beused, but in practice this may not be possible in a significant number of cases.

8.3 Non-compliant existing structures

Where existing structures do not comply with the above requirements appropriatepermanent signage and protective obstacles (fences and bollards) shall be put in place toachieve compliance/ control the hazards to safe levels, until such time as replacement can bejustified.



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8.3.1 Protective obstacle clearances (for mitigation of substandard clearances)

Figure 19: Protection against direct contact

Within outdoor installations a minimum protective obstacle clearance of N + 300 mm(minimum 600 mm) shall be maintained from live parts to the internal surface of anyprotective obstacle (see Figure 19 above).

Protective obstacles shall be located so that the minimum clearance from where an operatormay stand on the accessible side of the obstacle to the live part. This is determined by a tautstring distance of W.

Protective obstacles shall be a minimum height of 1200 mm and a maximum height of

1400omm to be effective.

Appropriate warning signage shall be provided.



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8.4 Modifications or extensions

Modifications/extensions to existing electrical structures must meet the requirements,spacings and distances in place at the time they were originally installed, and also meet thefollowing requirements:

1. Minimum phase phase and phase earth clearances as per Table 1 of this standard(the clearance values in brackets at the lower voltage levels may be applied for thispurpose).

Note: Table 1 clearances are generally lower than those in the predecessor documents. There havebeen a number of significant reductions in clearances since Electrical Design Standard DC3.1.2, 1974 was issued.

2. The minimum heights of live metal above ground level specified in Electrical DesignStandard DC 3.1.2, 1974 are satisfied.

Note: Minimum heights of live metal above ground level were revised by Transpower to accept thevalues specified in Electrical Design Standard DC 3.1.2, 1974 for existing older structures.Service Advisory TP.DS 62.01 SA1 which was issued on 20th April 2005 for this purpose, isnow superseded by this Issue of TP.DS 62.01, and which includes DC 3.1.2 as an appendix.

3. Maintenance access spacings as per original design shall not be reduced.

Note: It is particularly important that when bulk oil circuit breakers are being replaced, care is takento ensure that there are sufficient clearances for inspection and testing of the replacementcircuit breaker. This is because modern SF6 live tank circuit breakers typically have a greaterheight profile than designed for when bulk oil circuit breakers were installed in olderstructures. The clearances to the terminals of the SF6 live tank circuit breakers must besufficient to allow for connection of test equipment with adjacent equipment in service.

4. The original layout and patterning of equipment shall not be varied if the variationmeans that safety is compromised.

Note: Replacing existing equipment with equipment that requires more space in structures that haveminimal clearance is not permitted where the minimal clearances are significantly reduced.Minimal clearances typically occur in older structures where the voltage is < 50 kV. As aguide, if the clearance between ground and any part of the equipment and live metal is lessthan N + 2440 then the clearance is considered to be minimal. For example it is consideredunsafe practice to replace a 33 kV circuit breaker with a larger 66 kV circuit breaker if thisresults in the distance between the nearest live metal at the point of isolation and where earthsare to be applied is reduced.

5. Wherever reasonably practical compliance with the latest standard shall be achieved

during modification or extension.



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9 IMPULSE TESTED EQUIPMENT

The minimum basic electrical clearances in this standard are for untested equipment andmay differ from clearances offered on purchased equipment. There are fundamental

differences between the requirements for buswork and connections, and the requirementsfor the individually specified, works tested, equipment to which the busbars andconnections are attached. However, to achieve consistency of applied clearances andconductor spacings throughout outdoor switchyard structures the minimum phase toearth, and phase to phase clearances given in Tables 1 and 2 shall apply to all newequipment items.

9.1 Transformers

The minimum phase to phase and phase to earth clearance and terminal spacings fortransformers shall comply with IEC 60076-3 except that the minimum phase to phase andphase to earth clearance and spacings for 33 kV and below shall be 500 mm respectively.Spacings shall include an additional allowance of 150 mm for the space taken up by the

terminal connection.

The minimum distance from a transformer to another transformer, building or otherequipment shall comply with IEC 61936-1 (see also IEEE 979Guide for substation fireprotection). This only applies to new transformer bays. If an existing transformer bay isbeing upgraded then the opportunity should be taken to include a fire resistant wall if this ispracticable.


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A DEFINITIONSTerms in this standard are used as defined in TP.AG 10.02Transpower Glossary. Otherdefinitions are:

clearance: The distance between two conductive parts or between a live part and earthalong a string stretched the shortest way between these conductive parts (the taut stringdistance). (See also definition of taut string distance).

competent: An employee is competent when they can demonstrate to Transpower, at anytime, that they have the necessary knowledge, skills and experience to carry out work withina switchyard safely, to the standards used by Transpower.

danger zone: The zone defined by the minimum phase to earth clearance (N) aroundexposed live parts.

Note: Exposed includes insulated but not to full working voltage.

distance for inadvertent movement (Di): The distance, vertical (DiV) and/or horizontal(DiH), which is allowed for the inadvertent movement of both personnel and machines.

earthed: Effectively connected to the general mass of earth.

enclosure: Thepart providing protection of equipment against certain external influencesand protection against direct contact from any direction.

highest equipment voltage: The highest r.m.s value of phase to phase voltage for which theequipment is designed in respect of its insulation as well as other characteristics that relateto this voltage in the relevant equipment standards.

horizontal reach (Rh): The horizontal reach of a person allowed for the purposes of workingfrom a fixed work platform shall be 1440 mm.

horizontal work safety clearance (H): The minimum distance measured horizontally

between live parts and the equipment to be worked on. This distance includes an allowanceof 300 mm for use of hand held tools.

LIWV: Lightning Impulse Withstand Voltage.

live: Connected to a source of electrical supply or subject to hazardous induced orcapacitive voltage.

maintenance access width (Ma): The access width provided for maintenance access, andwithin which ladders and mobile elevating work platforms (MEWPs) from whichmaintenance is carried out are located.

maintenance clearance: A collective term for horizontal work safety clearance (H), verticalwork safety clearance (V), and walking access clearance (W).

maintenance zone: A zone comprising the equipment to be worked on, the surroundingmaintenance access width, and the associated space required for maintenance work, andwithin which work from pre-planned work platform locations may be carried out.

minimum height: Thesmallest permissible vertical clearance between accessible surfacesand live parts without protection against direct contact, or those parts that may be subject toa hazardous voltage.

minimum phase to earth clearance (N): Thesmallest permissible clearance in air betweenlive parts and earth or between live parts and parts at earth potential (values of N as perIEC 61936-1 are used in this design standard).

minimum phase to phase clearance: smallest permissible clearance in air between live

parts of different phases or between the same phase that are electrically separate fromanother.



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network security: A term used to describe the ability or capacity of a network to provideservice after one or more equipment failures. It can be defined by deterministic planningcriteria such as (n), (n-1), (n-2) security contingency. A security contingency of (n-m) at aparticular location in the network means that m component failures can be tolerated withoutloss of service.

nominal value: Thevalue of a quantity used to designate and identify a component, device,equipment or system.

nominal system voltage: Asuitable approximate value of voltage used to designate oridentify a system

Note: Any reference to nominal voltage means nominal system voltage.

protection against direct contact: Measures that prevent the body of a person or an object(reaching into the danger zone) persons coming into hazardous proximity to live parts orthose parts that could carry a hazardous voltage.

protective barrier: Thepart providing protection against direct contact from any usualdirection of access.

protective obstacle: Thepart preventing unintentional access to an area where safetyclearances will be infringed, but not preventing access to this area by deliberate action.

security fence clearance: Thesmallest permissible clearance, measured horizontally,between an external fence and live conductors.

SIWV: Switching Impulse Withstand Voltage.

spacings: Thedistances measured between centre lines of conductors or equipment.

standard person: Figure 2 shows the height and reach of the standard person. This is basedon AS 2067.

switchyard: An area, enclosed by a security fence, containing normally live conductors

and/or other exposed live material.

taut string distance: The distance between two parts measured along a taut string stretchedthe shortest way between those parts.

vertical reach (Rv): The maximum vertical reach of a person (2440 mm) measured from theaccessible surface or temporary work platform floor. The accessible surface is either groundlevel, or a fixed walkway.(This is based on AS 2067, and includes an allowance of 300 mm for use of a hand held tool)

vertical work safety clearance (V): The minimum distance measured vertically betweenlive parts and the work plane. This distance includes an allowance of 300 mm for use of ahand held tool.

voltage range I: Voltage in the range 1 kV < Um up to and including 245 kV.

voltage range II: Voltage in the range Um > 245 kV.

walking access clearance (W): Theminimum safe clearance distance, measured as a tautstring distance to be observed between normally exposed live parts and any accessiblesurface which a person may walk on (normally ground level) in an outdoor installation ofopen design.

Work plane: The work plane is taken to be at waist height (1000 mm) above the accessiblesurface or temporary work platform. 1000 mm is a nominal value that may be varied, butshould not be increased without careful consideration of the nature and duration of thework to be undertaken.


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B CONTROLLED DOCUMENT FEEDBACK FORM

If you would like to submit any feedback or suggestions to Transpower to improve this document,there are two ways you can do this. You can either complete the form below and fax it to: Controlled

Document Services, Transpower NZ Ltd, on 04-494 6738; or you can submit a form online - just lookfor the Controlled Document Feedback Form on the Contractors/Consultants section on our website atwww.transpower.co.nz.

Content change request No:

Date: Initiator's name/title:

Company: Phone: Fax:

Email:

Controlled document number: TP.

Controlled document title:

Affected section or clause number(s):

Present clause:

Proposed change:

Reason for change:

If you are including supporting information or attachments, please list here, e.g. photos:

clearances and conductor spacings

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