v3.0
Operation of SF6 Switchgear
OwnerName / Peter Vujanic
Title / Head of Health Safety and Environment
Signature
Date / 01 May 2016
Authoriser
Name / Dudley Sparks
Title / Operational Safety Manager
Signature
Date / 01 May 2016
This document forms part of the UK Power Networks Integrated Management System and compliance with its requirements is mandatory. Departure from these requirements may only be taken with the written approval of the above authoriser.
Revision RecordVersion number / 3.0 / What has changed?
Change of owner, changed on to new format. References updated.
Why has it changed?
Early review to bring in line with other DSR procedures.
Date published / 01/05/2016
Next review date / 01/05/2019
Prepared by / R Hembling
Version number / 2.0 / What has changed?
Changes after an Operational SAT review of the SF6 pints of isolation.
Why has it changed?
Date published / 20/05/2013
Next review date / 23/04/2016
Prepared by / D Sparks
Version number / 1.2 / What has changed?
Following feedback and advice from Asset Management we have removed the requirement to check POI gas pressures every 3 days. Also minor wording change to section 8.4.
Why has it changed?
Date published / 16/06/2011
Next review date / 27/05/2013
Prepared by / N Saunders
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Contents
1.0 Introduction and Purpose 3
2.0 Scope 3
3.0 Objective 3
4.0 References 4
5.0 Definitions 4
6.0 Responsibilities 4
7.0 Records 5
8.0 Process Detail 5
8.1 IDENTIFICATION 5
8.2 ROUTINE OPERATIONS 5
8.3 Points of Isolation 5
8.4 EFFECT OF LOSS OF GAS PRESSURE 7
8.5 Action to be taken following a gas alarm or gas lock out 8
9.0 Operative’s Flow Diagram 9
10.0 Superseded Documents 9
11.0 APPENDIX A 10
1.0 Introduction and Purpose
Sulphur hexafluoride (SF6) is an exceptionally stable gas which, in its pure form, is colourless, odourless, tasteless, non-toxic, and heavier than air. It is used in high voltage switchgear because of its excellent insulation and arc-quenching properties, but if the normal operating pressure is not maintained its ability to provide the required levels of insulation or to suppress an arc may be compromised.
When arcing occurs in SF6 the gas may break down into lower order fluoride compounds which are both toxic and corrosive. Under normal operating conditions no special precautions are required because a molecular sieve within the switch compartment will neutralise these compounds. This sieve has a long life but is degraded by excessive operations or moisture and oxygen introduced into the gas during top ups. If there is a serious leak of gas, or if an electrical arc ruptures the enclosure, the escaping gas may distribute toxic compounds. Additional safety and environmental precautions will then be required.
Sulphur hexafluoride is a powerful 'greenhouse gas' and consequently strict controls must be put in place to prevent any discharges into the atmosphere.
In normal circumstances SF6 is neither a health nor an environmental hazard so long as the Company's policies and procedures are correctly applied, but it is important to note that when entering an enclosed substation containing SF6 gas filled apparatus, operators must consider the risk of leaking gas reducing the oxygen in the atmosphere. See HSS 01 090, Access to and Working in Confined Spaces.
When entering a substation known to contain SF6-filled switchgear, if there is a foul sulphurous smell and/or white powder, there has probably been a fire or an explosion involving SF6 filled apparatus. In this case, do not touch anything. Leave the substation immediately and telephone Flashcall and AIRLine. HSS 01 039 Response to Environmental Incidents and HV Operation procedures shall be followed.
2.0 Scope
This procedure is supplementary to the UK Power Networks Distribution Safety Rules, and does not authorise any departure from them.
It applies to all apparatus containing SF6 connected to the High Voltage system.
This Procedure details the actions to be followed when carrying out routine switching and work on apparatus containing SF6. This work includes the action to be taken when there is a reduction in the gas pressure of SF6 switchgear; precautions required when SF6 switchgear is to be used as a point of isolation; and guidance on working within GIS gas zones.
The procedures to be used for top up, leak location and following an uncontrolled release of SF6 are given in EDS 03-0036 Management of Switchgear Containing SF6; HSS 01 005 Management of Sulphur Hexafluoride; and HSS 01 039 Response to Environmental Incidents.
3.0 Objective
To ensure the safety of staff operating and working on the UK Power Networks high voltage systems, and to provide an approved procedure for compliance with the UK Power Networks Distribution Safety Rules.
4.0 References
DSRs / UK Power Networks Distribution Safety RulesDSR 01 002 / HV System Operations
HSS 01 005 / Management of Sulphur Hexafluoride
FTR 12 / Emergency Response to Rapid Loss of SF6 From Switchgear Due to Electrical Fault. Inspect, make Safe and Restore Supplies
HSS 01 039 / Response to Environmental Incidents
EAS 07-0021 / Signs and Labels for Operational Sites and Equipment
EDS 03-0026 / 145kV and 72.5kV Gas Insulated Switchgear - gas zone identification and alarms
EDS 03-0036 / Management of Switchgear Containing SF6
FGAS Regs / Fluorinated Greenhouse Gas Regulations 2009
HSS 01 090 / Access to and Working In Confined Spaces
EU Regulation 842/2006 / Regulation of Certain Fluorinated Greenhouse Gases
COSHH 149 / Sulphur Hexafluoride (SF6)
ENA Engineering Recommendation G69/- / Guidance on Working with Sulphur Hexafluoride
5.0 Definitions
Terms used for normal system operations are defined in the UK Power Networks Distribution Safety Rules. Within this document such terms are identified by initial capital letters.SF6 Switchgear / Apparatus using SF6 for arc quenching and/or insulation.
Gas Insulated Switchgear (GIS) / Apparatus using SF6 gas for arc quenching and insulation with separated gas zones. GIS is normally found only on the 66kV and 132 kV systems.
6.0 Responsibilities
It is the responsibility of all staff who have been authorised to operate or work on the high voltage system to comply with this procedure.
7.0 Records
All operations on the UK Power Networks High Voltage network, including draining and filling gas pressure zones shall be agreed by the HV Control Engineer. The HV diagram in the Control Centre shall be dressed to reflect the current configuration of the distribution network and with any other relevant details (e.g. faulty apparatus, safety documents)
(see DSR 01 002 HV System Operations).
Gas zone diagrams for all GIS equipment are provided by the manufacturer or UKPN and placed at every site as part of the installation process.
Records of apparatus containing SF6 gas shall be maintained in Ellipse which are available to the Control Engineer at all times.
All details of gas top-ups shall be recorded in Ellipse and AIRLine. See EDS 03-0036
8.0 Process Detail
8.1 IDENTIFICATION
All sites at which SF6 is present shall be identified by a sign (see Appendix A) prominently displayed. The sign informs operators and the emergency services that special precautions will be required if a catastrophic failure has occurred.
In addition, to comply with EU Regulation 842/2006, all HV SF6 switchgear supplied since 2007 should have a data plate stating that the apparatus contains a fluorinated greenhouse gas, and the quantity of gas contained.
8.2 ROUTINE OPERATIONS
When entering an enclosed substation containing SF6 gas filled apparatus, operators must consider the risk of leaking gas reducing the oxygen in the atmosphere. See HSS 01 090 Access to and Working in Confined Spaces.
Where practical, before carrying out any local switching operations the pressure indicator on the gas filled container shall be examined to check that the gas pressure is within the operating range. If it is not, the switchgear shall not be operated Live, and the procedure given in section 8.4 shall be followed.
8.3 Points of Isolation
When using SF6 switchgear as a point of isolation:
· where practical the pressure of the gas shall be checked prior to the issue of any Safety Document
SF6 switchgear shall not be used as a point of isolation, or operated live where
· Where no gauge is fitted and no remote or local alarms or indications are fitted so the gas pressure cannot be confirmed
· it is found that the gas pressure is outside the operating range (the procedure given in section 8.4 shall be followed), or
· if it is unclear from the gauge or on receipt of control indications or alarms as to whether the gas pressure is within safe operating limits.
· if the switchgear cannot be operated by the electrical control system as this can be indication of the device being in the locked out state.
8.3.1 Working with SF6 switchgear
· The location of all SF6 switchgear used as a point of isolation shall be noted on any Safety Document at all voltage levels.
· A note shall be made on the Safety Document that gas pressures have been checked.
· Where practical the gas zone alarms for the point(s) of isolation shall be switched to 'audible' and the alarm checked back to control
· If a drop in gas pressure at a point of isolation results in an alarm or this becomes apparent while work is in progress, the work shall be suspended immediately and not resumed until remedial action has been taken (see section 8.4).
8.3.2 GIS Switchgear - work in a Gas Zone:
· Work in the Gas Zone shall be carried out only by staff or specialist contractors who have appropriate competency.
· An up to date, approved gas zone drawing is required to be available on site.
· When it is necessary to lower the pressure in a Gas Zone, it will be done under the personal supervision of the Senior Authorised Person in charge of the work.
· Unless the manufacturer advises otherwise, the gas pressure in Gas Zones adjacent to those in which work is to take place shall be reduced usually to 50% of the normal operating pressure (see diagram in 8.3.2.1 below).
· Details of the Gas Zone to be worked on and the gas zones with lowered pressure shall be recorded on the Safety Document and shall also be recorded by the Control Engineer.
· The lock(s) shall be removed from the Gas Zone to be worked on, by the Senior Authorised Person in the presence of the holder of the Safety Document.
· The Senior Authorised Person shall show the limits of the working zone to the holder of the Safety Document and members of the working party.
· If a Gas Zone in which pressure has been reduced houses an Isolating Device, the device cannot be used as a point of isolation. Consequently isolation must be made in a second Gas Zone away from the working zone. This may require an adjacent circuit to be switched-out.
· A safety lock and caution notice shall be applied to the gas connection points of Gas Zones adjacent to the working zone.
8.3.2.1 Gas Zone Diagram
8.4 EFFECT OF LOSS OF GAS PRESSURE
Should a gas leak occur, the integrity of the SF6 to act as an insulant or arc quenching medium is reduced. If the gas pressure falls below the safe operating level an alarm may be initiated and operation of the switchgear inhibited.
The automatic actions that will be initiated as a result of falling or low gas pressure may be one of the following, depending on the make and type of the switchgear:
· Ring Main Units using SF6 gas without external pressure gauge. The circuit-breaker trips when the gas pressure falls. The switchgear may remain in service with low gas pressure, but pressure must be restored before the circuit-breaker can be closed or the ring switches operated.
· Ring Main Units using SF6 gas with an external pressure gauge. When the pressure drops to below the safe operating pressure (the zone often marked in red) the switchgear must not be operated Live.
· Switchgear with both falling and low pressure alarms. The gas pressure must be topped-up when the 'falling' alarm is given. If a 'low pressure' alarm occurs the switchgear must not be operated Live.
· Switchgear with a low pressure alarm only. The gas pressure must be topped-up when the low alarm is initiated.
In all cases, if the pressure has fallen to atmospheric then operators must be aware that moisture or oxygen may have contaminated the remaining SF6. In these cases the tank must be evacuated first before gas is topped up. Instead seek advice from manufacturers, asset management or change the equipment.
In accordance with EDS 03-0036, equipment shall be made dead from remote ends prior to topping up.
Only in exceptional circumstance is it permissible to permanently feed gas via a regulator to maintain pressure.
8.5 Action to be taken following a gas alarm or gas lock out
Refer to EDS 03-0036, Management of Switchgear Containing SF6.
8.5.1 The Switching Operator shall:
· immediately notify the appropriate Control Engineer and report any alarm or automatic operation
· determine whether it is possible that moisture has entered the gas chamber
· If appropriate, make dead and arrange to have the gas topped up
· make an Airline report and report the amount of gas replaced