TP.DS 62.01
Issue 3
Feb 2009
Clearances and
conductor spacings
– and a safe access for a.c.
switchyards
TRANSPOWER
APPROVED
STANDARD
Implementation date: March 2009
COPYRIGHT © 2009 TRANSPOWER NEW ZEALAND LIMITED. ALL RIGHTS RESERVED.
This document is protected by copyright vested in Transpower New Zealand Limited (“Transpower”). No part of the document may be
reproduced or transmitted in any form by any means including, without limitation, electronic, photocopying, recording or otherwise, without
the prior written permission of Transpower. No information embodied in the documents which is not already in the public domain shall be
communicated 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.
TP.DS 62.01
Issue 3
Feb 2009
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 of
mobile elevated work platforms (MEWPs) in order to reduce fall hazards.
3.
Improve safety by requiring work plane heights to be aligned with the New Zealand
Department of Labour Code of Practice for Manual Handling (the design principles for manual
handling 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 to
circuit breaker mechanism boxes, and to prohibit designs based on the use of steps for this
purpose as per Service Advisory TP.DS 62.01 SA1 (now superseded by this document).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 on
insulating support columns.
6.
Improve safety by requiring existing installations that do not comply with minimum clearances
as determined by national and international standards to be remedied by restricting access and
use of warning signs.
7.
Improve circuit availability by requiring that routine maintenance and equipment change-outs
can 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 IEC
standards. The range of terms used has been significantly increased and these are defined in
Appendix A Definitions.
Because of the extensive nature of the changes in this third issue of TP.DS 62.01 the Revision History
log has been reset to restart again as at the date of issue.
Keywords
clearances
maintenance groups, zones,
and access
mobile elevating work
platforms (MEWPs)
protective barriers and
obstacles
provision for inadvertent
movement (Di)
spacings
walking access clearance (W)
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Revision History
Date
Issue
Amendments
Feb 2009
3
Refer to Preface on page 2.
CONTACT
This document is the responsibility of Engineering Services Group,
Transpower New Zealand Limited, Wellington. If you have any
queries 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 the
rear of this document or online via the Controlled Documentation
homepage of the Transpower website at www.transpower.co.nz
LIMITATION OF LIABILITY AND
DISCLAIMER OF WARRANTY
Transpower New Zealand Limited makes no representation or
warranties with respect to the accuracy or completeness of the
information contained in the document. Unless it is not lawfully
permitted to do so, Transpower specifically disclaims any implied
warranties of merchantability or fitness for any particular purpose
and shall in no event be liable for, any loss of profit or any other
commercial damage, including, but not limited to, special,
incidental, consequential or other damages.
CONFIDENTIALITY
All information disclosed in this document that is not general public
knowledge must be treated as strictly confidential and may not be
used or disclosed except for the purpose of developing documentation
for the benefit of Transpower.
© 2009 - Transpower New Zealand Limited
MINIMUM REQUIREMENTS
The requirements set out in Transpower’s standards are minimum
requirements that must be complied with by contractors, including
designers and other consultants. The contractor is expected to
implement any practices which may not be stated but which can
reasonably be regarded as good practices relevant to the purpose of
this standard. Transpower expects contractors to improve upon these
minimum requirements where possible and to integrate these
improvements into their procedures and quality assurance plans.
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TP.DS 62.01
Issue 3
Feb 2009
CONTENTS
PREFACE ............................................................................................................................2
1
PURPOSE............................................................................................................................5
2
POLICY................................................................................................................................5
3
COMPLIANCE.....................................................................................................................5
4
REFERENCES AND BACKGROUND MATERIAL ............................................................6
5
GENERAL REQUIREMENTS .............................................................................................7
6
7
8
9
5.1
Design Drawings .................................................................................................................7
5.2
Continuity in Service ..........................................................................................................7
5.3
Design Co-ordination .........................................................................................................7
5.4
Tables ....................................................................................................................................8
BASIC ELECTRICAL CLEARANCES............................................................................. 11
6.1
Requirements .....................................................................................................................11
6.2
Basic Electrical Clearances ...............................................................................................11
6.3
Increased Minimum Clearances Under Special Conditions .......................................11
6.4
Reduced Minimum Clearances Under Special Conditions.........................................11
CLEARANCES FOR SAFE ACCESS AND CONDUCTOR SPACINGS ........................ 12
7.1
Fundamental Design Requirement for Safety ...............................................................12
7.2
Walking Access Clearances..............................................................................................13
7.3
Minimum conductor heights ...........................................................................................14
7.4
Access for maintenance work ..........................................................................................15
7.5
Busbar Heights and Spacings ..........................................................................................23
7.6
Standard Clearances & Conductor Spacings.................................................................24
7.7
Alternative Clearances & Conductor Spacings .............................................................24
7.8
Low level equipment installations/ protective barriers (capacitors etc.)..................26
7.9
Access for Maintenance Vehicles and Plant ..................................................................27
7.10
Security Fence Clearances ................................................................................................33
7.11
Safe Access to Operational Equipment ..........................................................................33
EXISTING A.C. SWITCHYARDS ..................................................................................... 36
8.1
Policy requirements ..........................................................................................................36
8.2
Requirements for ground clearances and busbar heights ...........................................36
8.3
Non-compliant existing structures .................................................................................36
8.4
Modifications or extensions .............................................................................................38
IMPULSE TESTED EQUIPMENT .................................................................................... 39
9.1
Transformers......................................................................................................................39
APPENDICES
A
DEFINITIONS ................................................................................................................... 40
B
CONTROLLED DOCUMENT FEEDBACK FORM .......................................................... 42
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
1
PURPOSE
This standard defines minimum clearances to protect personnel, vehicles and equipment
against inadvertent contact, or hazardous proximity, to exposed conductors, and defines the
minimum basic clearances required in a.c. switchyards.
2
3
POLICY

All existing and new a.c. switchyards shall comply with New Zealand legal
requirements and the requirements of international and national standards, and New
Zealand industry documents as set out in Section 3, Compliance.

New a.c. switchyards shall be designed so that the required continuity in service of
energised equipment is maintained when nearby equipment is either maintained, or
replaced.

New a.c. switchyard layouts shall facilitate safe and efficient access by competent
employees who are carrying out operations and maintenance work using mobile
elevated work platforms where required. Where practical access for MEWPs shall
also apply to modifications and extensions to existing a.c. switchyards.
COMPLIANCE
The design of Transpower a.c. switchyards shall meet the minimum clearance requirements
of 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 external
clearances in air
Where conflict exists between the above documents they shall take precedence in the order
listed.
The design of Transpower a.c. switchyards shall facilitate compliance with the following
documents:

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 the
requirements of Section 8 Existing a.c. switchyards.
TP.DS 62.01
Issue 3
Feb 2009
4
REFERENCES AND BACKGROUND MATERIAL
The following documents are referred to in this standard or provided background material
for 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 transmission
lines, substations and underground, cables
TP.DG 47.01
Safety by design – strategy and application: elimination of hazards for
people, 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 Protection
Guidelines: 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 and
external 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 for
Manual Handling
New Zealand Department of Labour Code
HSE Act
Health and Safety in Employment Act 1992
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
5
GENERAL REQUIREMENTS
5.1
Design drawings
Design drawings for all new a.c. switchyards, and extensions, or modifications to existing
a.c. switchyards shall be prepared by the designer and submitted to Transpower for
approval. 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 maintenance
and 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 maintenance
All a.c. switchyards shall be designed so that routine maintenance can be safely carried out
without the need to remove from service, nearby energized equipment in other circuits.
Note that during replacement, upgrade or extension projects existing equipment within the
associated 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 to
remove 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), a
new circuit connected to that busbar shall be designed so that circuit breakers can be safely
replaced 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 without
the need to remove from service, nearby energized equipment in other circuits, including
sections of bus.
Example: To be able to replace the bus coupler circuit breaker and CTs with both adjacent
busbars live.
5.3
Design co-ordination
5.3.1
Switchyard layout and patterning
Replicable layouts that can be readily related to the single line diagram shall be used. The
equipment 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 fields
Close proximity to high voltage conductors can result in unacceptable exposure to electric
and magnetic fields.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Internal fences around air-cooled reactors and other areas of high magnetic fields shall
protect personnel outside the fence from magnetic fields in excess of the ICNIRP guideline
for occupational exposure.
TP.DG 30.01 Electric and magnetic field design parameters for a.c. 50 Hz transmission lines,
substations and underground, cables provides more specific requirements with regard to the
consideration of the limitation of EMF exposures during design.
5.4
Tables
Table 1: Minimum clearances for voltage range I: 1 kV < Um up to and including 245 kV
LIWV 1
Minimum phase to earth (N) &
phase to phase clearance
(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)
Nominal system
voltage
Highest equipment
voltage
Un
Um
(kV)
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 be
used to calculate maintenance clearances, protective barrier/obstacle clearances, or security
fence clearances.
3
110 kV lines which have a LIWV of 450 kVpk have a corresponding minimum clearance of
900 mm.
4
220 kV lines and transformers which have a LIWV of 950 kVpk (or 900 kVpk for
transformers prior to about 1982) have a corresponding minimum clearance of 1900 mm.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Table 2: Minimum clearances for voltage range II: Um > 245 kV
Nominal
system
voltage
Highest
equipment
voltage
Un
Um
(V)
(kV)
(kVpk)
(kVpk)
400
420
1425
1050
Note:
Rated
LIWV
Rated
SIWV
Minimum
phase to
earth
clearance
SIWV
Minimum phaseto-phase
clearance
(mm)
(kVpk)
(mm)
3400
1575
4200
N
The nearest IEC 61936-1 Nominal system voltage to 400 kV is 380 kV. Transpower has
selected a nominal system voltage of 400 kV. As the nominal system voltage is defined as a
suitable 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. voltages
from August 2008
Nominal
system
voltage
Minimum
busbar
(rigid type/
no sag)
clearance
height1
Busbar
spacing
centre line to
centre line for
rigid busbars
Minimum
vertical
work safety
clearance 1,3
V (includes
DiV of
1000 mm)
Minimum
horizontal work
safety clearance
1,3
H (includes DiH
of 1900 mm and
Ma of 1900 mm)
Un
Minimum
height of live
parts above
fixed
accessible
surfaces 1, 2
W
(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 not
included in the above table.
5.
Because the trend is to phase out 50 kV lines and a.c. switchyards these are not included in the
above table. Therefore for 50 kV installations design to 66 kV clearances.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Table 4: Revised safety distances as from 20th April 2005 to July 2008
Nominal system voltage
Minimum height of live parts
above fixed accessible
surfaces
Minimum busbar (rigid type/
no sag) clearance height
assuming 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
Un
Refer to Section 8.
Table 5: Acceptable safety distances for installations built prior to 20th April 2005
Nominal system voltage
Minimum height of live parts
above fixed accessible
surfaces
Minimum busbar (rigid type/
no sag) clearance height
assuming 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
Un
Refer to Section 8.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
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 protection
for personnel and equipment by reducing flashovers caused by system over-voltages and
lightning 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 earth
clearances (N) and phase to phase clearances. These clearances are used for a.c.
switchyard structures, conductors, and insulators etc. that, for practical reasons, have not
been tested for compliance with the LIWV type tests, either individually or as a total built
unit. 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 when
increased 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 may
require to be increased are as follows:
6.4
(a)
Minimum clearances between conductors of an installation that may be subject to
phase opposition shall be 20 % higher than the standard minimum values.
(b)
Minimum clearances between conductors of an installation, which are assigned to
different insulation levels, shall be 25 % higher than the standard minimum values
established 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 standard
minimum clearances shall be maintained as a minimum.
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 suitable
measures 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 to
Transpower.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
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 spacing requirements for new a.c. switchyards.
7.1
Fundamental design requirement for safety
Designs must ensure that competent personnel can carry out operating and maintenance
procedures without inadvertently encroaching within the danger zone.
The danger zone is defined by the minimum phase to earth clearance (N) to live
conductors.
Figure 1: Danger zone concept
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Feb 2009
7.2
Walking access clearances
New a.c. switchyards shall be designed to have minimum safe clearances from all surfaces
that are accessible to competent employees walking throughout the substation.
Figure 2: Minimum design dimensions for safe access
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
The minimum walking access clearance to live parts from accessible ground, or accessible
platforms 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 minimum
height of live conductors above fixed accessible surfaces given in Table 3 or the
walking access clearance W, where W= N + 2440. The clearance W is referenced to
the maximum conductor sag.
(b)
The lowest part of any insulation, for example the upper edge of metallic insulator
bases, 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 the
lowest live conductor is not always located at the equipment terminals.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
7.4
Access for maintenance work
New a.c. switchyard designs shall be based on the provision of safe and efficient
maintenance access from temporary elevated surfaces for all work that cannot be done from
ground level.
It shall be possible to locate temporary work platforms so that routine maintenance can be
carried out without the need for outages of equipment in other equipment maintenance
groups.
Standard designs shall not be based on the use of scaffolding/ climbing /ladders for routine
maintenance 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 retermination 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 work
platforms. For example, equipment should not be located in the area in front of a circuit
breaker, 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 units
etc. without requiring shutdown of any primary electrical equipment.
7.4.1
Equipment maintenance access groups
Equipment 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 and
inspection. A typical example of this is indicated in Figure 4.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Figure 4: SLD primary equipment maintenance groups
7.4.2
Equipment maintenance zones
Maintenance zones are based upon the maintenance access width, the volume occupied by
the equipment, and the work plane heights. Refer to Figures 5, 6 and 7 below.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
Issue 3
Feb 2009
Figure 5: CB/CT maintenance access envelope and zone – plan view
The required height of the temporary work platform is determined by the highest work
plane height. Generally, the highest work plane shall be at the same height as the highest
equipment point, and for ergonomic reasons, is taken as being located 1000 mm above the
work platform.
For circuit breakers the highest work plane shall be at the same height as the highest
terminals, and taken as being located 1000 mm above the work platform for ergonomic
reasons.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Feb 2009
Figure 6: Maintenance access envelope and zone – vertical view
A maintenance access width plus sufficient room to facilitate replacement of major
components, as well as replacement of the entire unit of equipment, shall be provided
around the periphery of all large equipment items such as transformers.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Feb 2009
Figure 7: Transformer maintenance access
It may not always be practical to provide an access width along each side of an item of
equipment in order to meet general requirements.
The maintenance access series of drawings TP58394 (refer subsection 5.1 above) is being
extended to show maintenance access arrangements as they become available for various
types of equipment.
7.4.3
Positioning of temporary elevated work platforms
Temporary elevated work platforms shall be able to be safely moved into the work position
without requiring outages of equipment other than the equipment to be worked on. The
component distances in Figures 8 and 9 have been selected to cater for a reasonably wide
range of MEWPs as used by contractors.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Figure 8: Mobile elevating work platforms – minimum design requirements
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Feb 2009
7.4.4
Work Position of Temporary Elevated Work Platforms
Once in position the required minimum clearances are as per Figure 9 below.
Figure 9: Boom type EWPs – heights and clearances
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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Feb 2009
7.4.5
Access using ladders
Where it is not possible to gain access using MEWPs, then access using ladders is
permissible for inspection purposes, but ladders are not to be used as work platforms.
Figure 10: Use of ladders – heights and clearances
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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7.4.6
Work safety clearances formula
For definitions of Di, (including DiV and DiH), Rv, and Rh, refer to the distance for
inadvertent movement, vertical reach and horizontal reach respectively in the definitions
section.
(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 for
DiH
Vehicle, or mobile plant in transit (subsection 7.9)
1000 mm for DiH, and 0 mm for DiV
All other applications, unless the type of
equipment justifies the use of a value of Di
0 mm
Ma values to be used:
MEWP boom or stick type
1900 mm
Scissor 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 heights
Generally busbar mounting heights are to comply with Table 3 to allow vehicles and plant
to pass underneath. The required height is to the lowest part of the busbar. For vertically
spaced 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 designed
such that under the worst combination of conditions the minimum height at any point shall
not be less than that required by Table 3.
Busbars mounted in a special enclosure, which prevents access to personnel while the
equipment is live, may be mounted at any height sufficient to give phase to earth clearances
in accordance with Table 1 and 2. In such cases protective barriers shall be installed in
accordance with subsection 7.8.
© 2009 - Transpower New Zealand Limited
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TP.DS 62.01
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7.5.2
Busbar horizontal spacings
The centre line to centre line spacings in Table 3 allow for the installation of the typical
designs of disconnectors and earth switches in line with the busbars. The typical
disconnectors 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 also
accommodated at 72.5 kV, 123 kV and 245 kV. For single side break disconnectors the
spacings must be increased.
The spacings are also suitable for in-line installation of current transformers and circuit
breakers.
Vertically-spaced busbars must meet the requirements of Table 1 and 2, after making due
allowance for flexibility, etc.
Flexible or strung busbars require greater spacings to allow for side swing and the
separation of bundled conductors.
7.6
Standard clearances and conductor spacings
Table 3 summarizes the above subsections and gives the minimum vertical and horizontal
work 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 to
Transpower provided they meet the policy requirements, and meet:
1.
The walking access and minimum equipment height requirements as set out in
Table 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 the
Manager responsible for this standard and approval of the manager responsible for
equipment maintenance.
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TP.DS 62.01
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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 may
propose an alternative solution for Transpower’s consideration, or request advice from
Transpower on alternative acceptable solutions. For example, in the case of scissor type
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TP.DS 62.01
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MEWPs a value of Ma less than 1900 mm may be proposed if suitable narrower mobile
equipment 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 protective
obstacles and appropriate warning signage to ensure that competent employees can walk
safely 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 carrying
out routine inspections, operations or maintenance to a safe distance from the live parts.
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TP.DS 62.01
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Either solid or mesh barriers shall be used as per Figure 12. Barriers with openings
exceeding 50 mm shall not be used.
For non-rigid protective barriers and wire meshes, the clearance values shall be increased to
take 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
Clearances
The access envelopes designed for maintenance vehicles and plant shall include provision
for inadvertent movement, provision for door opening, and shall have a clearance from
overhead conductors and other live parts, equal to, or greater than the reduced minimum
approach distance given in NZECP 34 Table 6 plus 100 mm. (Refer to Figures below).
7.9.2
Under station busbars
Mounting heights for flexible busbars and other sections of live conductor under which
vehicles may pass shall be designed such that under the worst combination of conditions the
minimum height at any point shall not be less than that given in Table 3. This is for the
passage of maintenance equipment underneath busbars on the basis that such equipment
movements 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 the
equipment is live, may be mounted at any height sufficient to give phase to earth clearances
in accordance with Tables 1 and 2.
7.9.3
Primary equipment excluding transformers
To 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 meet
the following criteria:
1.
As a minimum straight through access shall be available between every second
diameter from one side of the structure to the other.
2.
The access route and area provided shall be suitable for the following MEWPs and
crane:
(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 these
types 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 figures
below.
Note, the above crane and MEWPs have been selected solely for the purpose of ensuring
that design access envelopes cater for a reasonable range of mobile plant that the
maintenance contractors may need to use for typical bay equipment.
7.9.4
Transformer or heavy item access
Formed heavy transport routes shall be provided for the installation and removal of
transformers 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 a
minimum width of 3000 mm and a minimum height of 4500 mm. Actual transformer
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TP.DS 62.01
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dimensions, and lifting arrangements etc. should be specified during the design phase, and
appropriate 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. An
appropriate 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 conductors
of RMAD + 100 mm.
Equipment shall be located so that no outages are required during movement of the
transporter with or without the transformer loaded.
If the required space for access is not possible because of site restrictions, warning signs
shall be attached to structures at a height of approximately 2,400 mm to their underside and
stop lines shall be painted across the access route.
7.9.5
Equipment mounted on high structures
Safe 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 primary
equipment from service. For example in some cases a high reaching type MEWP such as a
Genie S-65 may be required.
7.9.6
Calibration vehicle and trailer access
At sites where revenue metering is carried out at voltages above 33 kV, access shall be
provided for the calibration vehicle and trailer to be safely parked within 4,000 mm of the
instrument transformers that require calibration.
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TP.DS 62.01
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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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TP.DS 62.01
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Figure 15: Vehicle access between live bays
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TP.DS 62.01
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7.9.7
Vehicle & plant access around structure perimeters
Wherever practicable, a vehicle access route shall be provided all the way around the inside
of 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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TP.DS 62.01
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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 types
listed 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:
7.10
(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 loaded
and turning/ slewing, or when a crane is lifting an equipment item such as a circuit
breaker onto a transport truck.
Security fence clearances
The clearances/ distance between switchyard perimeter security fences and equipment shall
comply 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 minimise
equipment outages for maintenance work.
For maintenance purposes the top of the security fence is to be treated as a work plane, and
the 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 34
apply with regard to vertical height of the conductor above the ground and the top of the
fence.
7.11
Safe access to operational equipment
7.11.1
Equipment mechanism boxes
Safe access from an accessible surface (normally at ground level) shall be provided for
operational or in-service inspection purposes of equipment mechanisms, counters, gauges,
mechanism boxes etc.
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TP.DS 62.01
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Figure 17: Live tank CB installation
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TP.DS 62.01
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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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TP.DS 62.01
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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 for
vehicle access under busbars, as scheduled in Tables 4 and 5 in subsection 5.4, apply to
existing structures. The clearances and heights in Table 4 apply to structures designed after
20th April 2005 to July 2008, while those in Table 5 apply to structures designed before 20th
April 2005.
Tables 4 and 5 give the height above normally accessible ground for access within a fenced
structure area, in which live metal other than busbars, i.e. not exceeding 1 m in any
horizontal dimension, may be mounted. This permits some flexibility to cater for different
arrangements of the connections between equipment terminals and overhead busbars, but
the transition to the busbar height should be made as close as reasonably possible to the
equipment terminals. Ideally vertical droppers onto the equipment terminals would be
used, 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 appropriate
permanent signage and protective obstacles (fences and bollards) shall be put in place to
achieve compliance/ control the hazards to safe levels, until such time as replacement can be
justified.
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TP.DS 62.01
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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 any
protective obstacle (see Figure 19 above).
Protective obstacles shall be located so that the minimum clearance from where an operator
may stand on the accessible side of the obstacle to the live part. This is determined by a taut
string 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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TP.DS 62.01
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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 the
following 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 this
purpose).
Note: Table 1 clearances are generally lower than those in the predecessor documents. There have
been a number of significant reductions in clearances since Electrical Design Standard DC
3.1.2, 1974 was issued.
2.
The minimum heights of live metal above ground level specified in Electrical Design
Standard DC 3.1.2, 1974 are satisfied.
Note: Minimum heights of live metal above ground level were revised by Transpower to accept the
values 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, is
now 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 taken
to ensure that there are sufficient clearances for inspection and testing of the replacement
circuit breaker. This is because modern SF6 live tank circuit breakers typically have a greater
height profile than designed for when bulk oil circuit breakers were installed in older
structures. The clearances to the terminals of the SF6 live tank circuit breakers must be
sufficient 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 variation
means that safety is compromised.
Note: Replacing existing equipment with equipment that requires more space in structures that have
minimal 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 a
guide, if the clearance between ground and any part of the equipment and live metal is less
than N + 2440 then the clearance is considered to be minimal. For example it is considered
unsafe practice to replace a 33 kV circuit breaker with a larger 66 kV circuit breaker if this
results in the distance between the nearest live metal at the point of isolation and where earths
are 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 and
may differ from clearances offered on purchased equipment. There are fundamental
differences between the requirements for buswork and connections, and the requirements
for the individually specified, works tested, equipment to which the busbars and
connections are attached. However, to achieve consistency of applied clearances and
conductor spacings throughout outdoor switchyard structures the minimum phase to
earth, and phase to phase clearances given in Tables 1 and 2 shall apply to all new
equipment items.
9.1
Transformers
The minimum phase to phase and phase to earth clearance and terminal spacings for
transformers shall comply with IEC 60076-3 except that the minimum phase to phase and
phase 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 other
equipment shall comply with IEC 61936-1 (see also IEEE 979 Guide for substation fire
protection). This only applies to new transformer bays. If an existing transformer bay is
being upgraded then the opportunity should be taken to include a fire resistant wall if this is
practicable.
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APPENDIX A
A
TP.DS 62.01
Issue 3
Feb 2009
DEFINITIONS
Terms in this standard are used as defined in TP.AG 10.02 Transpower Glossary. Other
definitions are:
clearance: The distance between two conductive parts or between a live part and earth
along a string stretched the shortest way between these conductive parts (the taut string
distance). (See also definition of taut string distance).
competent: An employee is competent when they can demonstrate to Transpower, at any
time, that they have the necessary knowledge, skills and experience to carry out work within
a switchyard safely, to the standards used by Transpower.
danger zone: The zone defined by the minimum phase to earth clearance (N) around
exposed 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: The part providing protection of equipment against certain external influences
and protection against direct contact from any direction.
highest equipment voltage: The highest r.m.s value of phase to phase voltage for which the
equipment is designed in respect of its insulation as well as other characteristics that relate
to this voltage in the relevant equipment standards.
horizontal reach (Rh): The horizontal reach of a person allowed for the purposes of working
from 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 allowance
of 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 or
capacitive voltage.
maintenance access width (Ma): The access width provided for maintenance access, and
within which ladders and mobile elevating work platforms (MEWPs) from which
maintenance is carried out are located.
maintenance clearance: A collective term for horizontal work safety clearance (H), vertical
work safety clearance (V), and walking access clearance (W).
maintenance zone: A zone comprising the equipment to be worked on, the surrounding
maintenance access width, and the associated space required for maintenance work, and
within which work from pre-planned work platform locations may be carried out.
minimum height: The smallest permissible vertical clearance between accessible surfaces
and live parts without protection against direct contact, or those parts that may be subject to
a hazardous voltage.
minimum phase to earth clearance (N): The smallest permissible clearance in air between
live parts and earth or between live parts and parts at earth potential (values of N as per
IEC 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 from
another.
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APPENDIX A
TP.DS 62.01
Issue 3
Feb 2009
network security: A term used to describe the ability or capacity of a network to provide
service after one or more equipment failures. It can be defined by deterministic planning
criteria such as (n), (n-1), (n-2) security contingency. A security contingency of (n-m) at a
particular location in the network means that m component failures can be tolerated without
loss of service.
nominal value: The value of a quantity used to designate and identify a component, device,
equipment or system.
nominal system voltage: A suitable approximate value of voltage used to designate or
identify 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 or
those parts that could carry a hazardous voltage.
protective barrier: The part providing protection against direct contact from any usual
direction of access.
protective obstacle: The part preventing unintentional access to an area where safety
clearances will be infringed, but not preventing access to this area by deliberate action.
security fence clearance: The smallest permissible clearance, measured horizontally,
between an external fence and live conductors.
SIWV: Switching Impulse Withstand Voltage.
spacings: The distances measured between centre lines of conductors or equipment.
standard person: Figure 2 shows the height and reach of the standard person. This is based
on 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 stretched
the shortest way between those parts.
vertical reach (Rv): The maximum vertical reach of a person (2440 mm) measured from the
accessible surface or temporary work platform floor. The accessible surface is either ground
level, 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 between
live parts and the work plane. This distance includes an allowance of 300 mm for use of a
hand 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): The minimum safe clearance distance, measured as a taut
string distance to be observed between normally exposed live parts and any accessible
surface which a person may walk on (normally ground level) in an outdoor installation of
open design.
Work plane: The work plane is taken to be at waist height (1000 mm) above the accessible
surface or temporary work platform. 1000 mm is a nominal value that may be varied, but
should not be increased without careful consideration of the nature and duration of the
work to be undertaken.
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APPENDIX B
B
TP.DS 62.01
Issue 3
Feb 2009
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 look
for the Controlled Document Feedback Form on the Contractors/Consultants section on our website at
www.transpower.co.nz.
No:
Content change request
Date:
Initiator's name/title:
Company:
Phone:
Fax:
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Controlled document number:
TP.
Controlled document title:
Affected section or clause number(s):
Present clause:
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Reason for change:
If you are including supporting information or attachments, please list here, e.g. photos:
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