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Electrical
Switchgear and Safety:
A concise guide for users
www.hse.gov.uk
Translated to Persian by: Taghi Vahidi, April 2007
(Note: The Persian translation of this article is available in
the Persian section of the website) Introduction
This leaflet is aimed at owners and operators of electrical
switchgear in industrial and commercial organisations who have
little knowledge and expertise available in-house on electrical
matters. It summarises the comprehensive advice given in the HSE
guide keeping electrical switchgear safe, which is aimed at
organisations employing electrical engineering managers and
specialists (see ‘Further reading’).
The leaflet provides guidance on the managing of three-phase
electrical switchgear with voltage ratings from 1000-33 000 volts
alternating current (ac). It covers selection, use, care and
maintenance. The equipment covered includes switchgear using oil,
air, sulphur hexafluoride or vacuum as the interrupting medium. The
leaflet deals with circuit-breakers, switches, switch fuses and
isolators and also covers contactors operating at voltages above
1000 volts alternating current (ac). It does not cover direct
current (dc) switchgear, low-voltage switchgear (voltages up to 1000
volts ac) and switchgear used on single-phase alternating current
(ac) traction systems.
The advice contained in the leaflet will help you to keep your
electrical switchgear safe and comply with The Health and Safety at
Work etc Act 1974, the Management of Health and Safety at Work
Regulations 1999 and the Electricity at Work Regulations 1989.
In general, switchgear has a proven record of reliability and
performance. Failures are rare but, where they occur, the results
may be catastrophic. Tanks may rupture and, with oil-filled
switchgear, this can result in burning oil and gas clouds, causing
death or serious injury and major damage to plant and buildings in
the vicinity. Failures of switchgear can also result in serious
financial losses.
The use of modern switchgear containing sulphur hexafluoride gas
and/or vacuum has removed the hazard of burning oil but inevitably
has introduced other risks that need to be managed. Accident
experience has shown that failure usually occurs at, or shortly
after, operation of the equipment. How switchgear is operated, its
condition and the circumstances existing in the electrical network
at the time of operation, can affect its ability to perform safely.
Managing switchgear
If you use switchgear you are required by law to provide management
systems that will ensure safe operation and minimise the risk of
injury. Such management systems should include the following:
● an appropriate system of records;
● policies and procedures covering the installation, commissioning,
operation, maintenance and removal of the equipment;
● definitions of responsibilities and training requirements for your
people;
● an auditing regime to monitor and maintain the effectiveness of
procedures.
Records
Check that the records of all switchgear in service, network
diagrams and configurations, including prospective fault level
values at every relevant point on the system, are available and up
to date. If no records are found you will need to prepare these as a
matter of urgency.
The switchgear record should include:
● a diagram(s) of the electrical network showing the
interconnections between the various plant items including the
switchgear and their location(s);
● fault levels at all relevant points;
● types of equipment as part of an asset register, which needs to
include details such as manufacturer and type, serial number and
year of manufacture, date of installation, voltage
and current rating, short-circuit rating and type of operating
mechanism;
● details of operational limitations due, for example, to the
possibility of overstressing;
● a maintenance record of each item of switchgear;
● the number of fault clearance operations since circuit-breakers
were last maintained (if known);
● details of any modifications carried out, for example the fitting
of anti-reflex control handles; and
● whether there are arc control devices for oil-filled
circuit-breakers.
The basic records in the case of a low-voltage installation may also
contain electrical installation certificates and periodic inspection
reports. See BS 7671 2001: Requirements for Electrical Installations
(IEE Wiring Regulations, Sixteenth Edition).
Policies and procedures
Safety of the equipment
Using the information in the records, you should assess the
switchgear and the electrical network to identify any potential
risks and problems. These can include overstressing of switchgear,
presence of equipment having dependent manual operation, absence of
anti-reflex control handles and inadequate means of protection
against fire.
From this assessment you will be able to identify the necessary
remedial action(s) you need to take to ensure that the equipment and
systems are being operated safely.
Actions you may need to take urgently could include:
● prohibiting operation of overstressed switchgear when live,
including disabling automatic operation to clear faults on the
system. This will involve adjustments to electrical protection
upstream to ensure the system remains protected;
● preventing access to the switchgear when live;
● reducing fault levels wherever possible by reconfiguring the
network;
● prohibiting the operation of dependent manually operated
switchgear when live, except under very carefully controlled
conditions;
● replacing overstressed switchgear.
Further actions you may need to take (the urgency of which will
depend on the results of your assessment) could include:
● replacing overstressed switchgear;
● when possible, replacing the closing mechanism for dependent
manually operated switchgear. When this is not possible, you will
need to replace the switchgear;
● fitting anti-reflex handles;
● improving measures for protection against fire.
If you do not have sufficient technical expertise in-house to carry
out an assessment and decide on the appropriate actions, you should
take advice from and employ suitably competent persons/organisations,
such as:
● electricity distribution companies;
● switchgear manufacturers;
● switchgear maintenance companies with particular expertise in
older types of switchgear;
● consulting organisations specialising in switchgear.
Once you have decided on the actions you need to take, you should
develop a plan and timetable to carry them out.
Operating procedures
You should develop operating procedures and select the appropriate
category of people for the activities needed for operating,
inspecting, repairing, maintaining and testing the switchgear. In
all cases, the people you employ will require the appropriate
knowledge of the safety rules and will need to know how to apply the
safety documents. You will also need to tell them their
responsibilities to ensure safety and for safe working. Their level
of knowledge of the switchgear could range from a general
understanding to detailed technical knowledge depending upon the
duties you expect them to have.
Electricity distribution companies, training companies, switchgear
manufacturers and technical services companies may employ people who
are adequately trained and competent to operate the network and
maintain the switchgear. Where you have little knowledge and
expertise available in-house on electrical matters, one option is to
employ them to do some or all of these activities. You should
certainly consider employing someone in-house who is competent to
deal with emergencies.
To ensure that the different activities that are associated with
switchgear are performed competently and to the safety rules, it is
also important to define different categories of people, for example
competent and authorised persons. This allows you to clearly define
the duties that are expected of them, and what they are not
authorised to do. Training courses can be prepared to meet the
requirements of these categories.
Safety rules and safety documents
You should develop and implement safety rules and a safety
documents scheme (for example use of limitation-of-access and
permit-to-work forms) because they are fundamental to safety in the
use, care and maintenance of plant. The correct use of the safety
rules and safety documents is essential.
Responsibilities and training
People operating, inspecting, maintaining and testing your
switchgear will need to be made familiar with the procedures, safety
rules and safety documents (particularly for high-voltage
switchgear). You will also need to tell them their responsibilities
to ensure safety and safe working.
As a user of switchgear you are required by law to ensure the people
you have selected to be competent persons or authorised persons
receive the necessary training so that they are able to carry out
their duties in safety and without risk to health. The following
organisations offer a full range of training courses, from general
appreciation of site access and responsibilities through to detailed
courses on operations, safety and maintenance practice:
● electricity distribution companies;
● training companies;
● switchgear manufacturers;
● technical services companies.
Auditing regime
It is very important that you implement an auditing regime
to ensure that the procedures you have developed are being operated
properly. It should also include means to identify and rectify
defects in the systems (need for training or retraining etc).
Inspecting and maintaining switchgear
You should regularly inspect, maintain and test all switchgear and
its environment, for example the switchroom. In all cases you should
do this in accordance with the manufacturer’s instructions.
This leaflet cannot cover in detail those aspects of inspection and
maintenance particular to each type of switchgear (oil, sulphur
hexafluoride and/or vacuum). Also, materials such as oil and sulphur
hexafluoride have their own requirements for handling, cleaning,
avoidance of contamination, disposal and recycling. There are also
hazards associated with their use.
Inspection
You should inspect substations regularly. During the
inspection work you should prioritise any remedial actions as
follows:
● immediately (this should always be the case when security of the
substation enclosure has been interfered with);
● earliest possible opportunity;
● next scheduled maintenance.
You should include the following items in the inspection schedule:
● switchgear environment (switchroom access and surrounds, including
fence and external walls if outdoors), signs of water getting
in/dampness, signs of unauthorised access and/or interference,
condition of firefighting equipment and warning notices, and general
housekeeping;
● signs of abnormal conditions such as high temperature, smell of
hot substances or ozone, presence of smoke, signs of fresh leakage
of oil or compound, distortion and evidence of sooting on
enclosures;
● general condition of switchgear, such as corrosion, evidence of
leaks, fluid levels, presence/condition of labels, padlocks and key
exchange interlocks, condition of instruments and protection
equipment;
● condition of ancillary equipment such as batteries and chargers,
control panels etc.
Maintenance
You should do this at regular pre-determined intervals by,
for example, time-based preventative maintenance - see below. You
should also do it, particularly in the case of oil-filled
circuit-breakers, immediately after it has operated to switch off an
electrical fault in the network. Certain types of switchgear (such
as that using sulphur hexafluoride and vacuum) are sometimes
designated or described as ‘low maintenance’. However, you should
not interpret this to mean that no maintenance is required.
Time-based preventative maintenance
This system of carrying out maintenance at regular,
pre-determined intervals has been in use for many years. You decide
the frequency of maintenance from factors such as:
● the type of switchgear;
● whether it uses oil, sulphur hexafluoride or vacuum interruptors;
● its age; and
● how often it is operated.
You should also take the maintenance history of the switchgear into
account. You should keep records for each item so you can identify
aspects such as deterioration in the condition of the equipment. You
can then adjust the period between each maintenance accordingly.
Selecting new, replacement or Refurbished switchgear
When your assessment shows that switchgear needs to be replaced you
should consider the following options, taking advice as necessary.
Replacing the switchboard in its entirety
This has the advantage that a completely new switchboard
installation will use the latest designs on offer from
manufacturers.
Replacing/refurbishing switchgear in the existing installation
You will have a number of options:
● replace the individual switchgear units (moving and fixed
portion);
● refurbish the switchboards or individual switchgear units;
● retrofit the switchgear (this usually applies to
circuit-breakers).
Factors to take into account before selecting switchgear
Before you can decide you need to obtain assurance that the
high-voltage insulation components of the busbar system, current
transformer chambers, cables and terminations etc have adequate
remaining life to justify the costs of partial replacement,
refurbishment or retrofitting. It is essential that an overall
assessment of the switchgear is carried out. This includes a
condition assessment of the high-voltage insulation by using partial
discharge measurement techniques and the evaluation of available
test data and relevant standards. Where circuit-breakers are under
consideration, you also need to consider the:
● condition of the secondary wiring, protection and control
equipment;
● interlocking and earthing arrangements in relation to current
safety standards;
● short-circuit ratings;
● venting arrangement (where appropriate);
● rating of the existing (fixed) equipment is adequate to ensure the
replacement equipment can be used to its full rating.
The availability of spares plays a role in the decision process. You
should ensure that both strategic items (eg bushings, current
transformer chambers, cable boxes, operating mechanisms) and routine
maintenance items (eg arcing contacts, turbulator inserts, gaskets,
tripping and closing coils) are available. Do this by contacting the
original equipment manufacturers, their successor companies (if no
longer trading) or small specialist engineering companies.
Only then can you evaluate the economics of refurbishment/retrofit
against replacement.
Second-hand equipment
You can buy second-hand switchgear from companies
specialising in the recovery of redundant switchgear and in its
refurbishment for re-sale. But you need to be sure you only deal
with reputable and experienced organisations. Such organisations are
required to provide documentation on the use and maintenance of the
equipment they sell. This would include information originating from
the original equipment manufacturers. The companies supplying the
refurbished equipment should ensure all relevant items are dealt
with during overhaul, upgrades, modifications etc. However, you
could employ an independent consultant to oversee the contract. This
can be a worthwhile safeguard against purchase of unsuitable
equipment that might turn out to be not fit for purpose.
Measures to limit fires
Failure of switchgear can lead to fires and where oil-filled
equipment is involved the incident can be major. A serious incident
not only poses potential fire and smoke risks to people in the
vicinity and to the building fabric but may also affect other plant.
You should therefore carefully consider the measures you need to
take and put in improvements where necessary. There are a number of
techniques that can be used singularly or in combination to mitigate
the effects of a fire and limit smoke spread.
Compartmentation
You can separate substation plant items by fire-resisting
barriers to limit the extent of any fire to the item affected, but
it is important this does not inhibit any venting that may be
required to safeguard against explosion. Also, if you have automatic
fire extinction or control then compartmentation is useful.
Control and extinction
Fire-extinguishing systems use extinguishing mediums such as
halon and carbon dioxide. Halon is not an ideal choice because of
environmental considerations but its use may be necessary in areas
where fire hazards are particularly severe and could affect adjacent
plant.
These systems require the flooding of fire compartments and often
are arranged to operate automatically on detection of a fire. You
should ensure that secure measures to make the system non-automatic
are available for use by people before entering the protected area.
Suitable warning notices and instructions should be prominently
displayed at the point(s) of access to the area. These instructions
should also be included in the safety rules.
You should also review the use and provision of portable fire
extinguishers and the procedures for checking these and any
permanent systems. Where problems are identified in design,
operation or during inspections you should ensure corrective actions
such as replacement, recharging and relocation etc are taken.
Fire prevention and detection
The most appropriate control measure is prevention.
Strategies you should consider are:
● good management of the plant items, for example careful control of
workmanship. There is a greater likelihood of an incident occurring
after replacement or maintenance of equipment;
● careful monitoring of any degradation of oil and dielectric
insulation;
● reduction of possible ignition sources;
● good housekeeping.
An appropriate automatic fire detection system could provide the
electrical plant room or area with early fire detection and alarm
features. This could also be linked with a control/extinction system
to provide fast-response fire suppression or control.
Further reading
Keeping electrical switchgear safe HSG230
HSE Books 2002 ISBN 0 7176 2359 9
BS 6626: 1985 Code of Practice for maintenance of electrical
switchgear and controlgear for voltages above 1 kV and up to and
including 36 kV
British Standards Institution BS 6423: 1983 Code
of Practice for maintenance of electrical switchgear and controlgear
for voltages up to and including 1 kV
British Standards Institution
BS 7671: 2001 Requirements for Electrical Installations (IEE Wiring
Regulations, Sixteenth Edition)
Institution of Electrical Engineers (see ‘Other sources of
advice’ for address)
Further information
British Standards are available from BSI Customer Services,
389 Chiswick High Road, London W4 4AL
Tel: 020 8996 9001 Fax: 020 8996 7001
Website: www.bsi-global.com
HSE priced and free publications are available by mail order from
HSE Books, PO Box 1999, Sudbury, Suffolk CO10 2WA
Tel: 01787 881165 Fax: 01787 313995
Website: www.hsebooks.co.uk
(HSE priced publications are also available from bookshops and
free leaflets can be downloaded from HSE's website: www.hse.gov.uk.)
For information about health and safety ring
HSE's Infoline Tel: 08701 545500 Fax: 02920 859260
e-mail: hseinformationservices@natbrit.com or write to
HSE Information Services, Caerphilly Business Park, Caerphilly CF83
3GG.
Other sources of advice
British Electrotechnical and Allied Manufacturers Association (BEAMA)
Westminster Tower
3 Albert Embankment
London
SE1 7SL
Tel: 020 7793 3000
Fax: 020 7793 3003
The Institution of Electrical Engineers (IEE)
PO Box 96
Stevenage
SG1 2SD
Tel: 01438 767328
Fax: 01438 742792
e-mail: sales@iee.org.ukThis leaflet contains notes
This leaflet contains notes on good practice which are not
compulsory but which you may find helpful in considering what you
need to do.
This leaflet is available in priced packs of 5 from HSE Books, ISBN
0 7176 2187 1.
Single free copies are also available from HSE Books.
© Crown copyright This publication may be freely reproduced, except
for advertising, endorsement or commercial purposes. First published
04/03.
Please acknowledge the source as HSE.
INDG372 6/04
C60
Printed and published by the Health and Safety Executive
www.hse.gov.uk/pubns/indg372.pdf
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