NG TGN(E) 217 PDF

PURPOSE AND SCOPE

As part of the risk assessments for deferring maintenance or work not done, one of the mitigating actions may be to impose a Risk Management Hazard Zone (RMHZ).

The purpose of this document is to give guidance to staff on applying Risk Management Hazard Zones on plant and equipment. It seeks to give the size of the zone required; the reasoning for the zone and the amount of time staff can spend in the zone.

Maintenance is undertaken for many reasons and is normally undertaken to give appropriate balance of maintenance, cost and reliability. This document only focuses on the safety issue when maintenance is not undertaken at the appropriate time. It does not consider the other issues that occur due to not maintaining assets at the best time, for example, operational cost, environmental impact, and reliability etc.

This document considers safety only for equipment associated with outage maintenance and does not imply plant and equipment is reliable or satisfactory and guidance is dependant on completion of routines.

This document addresses the criteria, guidance and justification of imposing Risk Management Hazard Zones on substations. It is driven by the safety risk to persons that credibly could be attributed to overdue maintenance and or Work Not Done only. This document does not address any other aspect of risk and is not to override or undermine Operation Engineering & Safety Bulletins (OESB) etc.

As part of recording decisions and evidence in support of the application of generic Risk Management Hazard Zones, this paper has also looked at potential failure modes as a result of overdue maintenance for specific designs to assist in defining the appropriate size of the zone.

Generally the risk assessment includes minimum checks / tests that can be carried out to avoid a RMHZ, e.g. the full maintenance may not be achievable, but it may be possible to carry out work / testing to prove integrity of the equipment. In some cases, ensuring completion of the mitigations removes the need to establish a RMHZ. This will be communicated and controlled by the planning process.

Equipment considered:

a) Air Blast Circuit Breakers – Conventional Air Blast (ABCB – CAB)

b) Air Blast Circuit Breaker - Pressurised Head Air Blast (ABCB – PAB)

c) Oil Circuit Breakers (OCB) & Barrier Bushings

d) Gas Circuit Breakers (GCB) (SF6) – AIS

e) Switch Disconnectors

f) Disconnectors

g) Cables

h) Cable Sealing Ends (CSE)

i) Instrument Transformers

j) Supergrid Transformers, Bushings & Tapchangers

k) GIS equipment

l) Through Wall / Floor Bushings

Failure modes documented in the AHR (Asset Health Review) and OESBs imposing a RMHZ on switchgear were reviewed. The OESB investigations provided information on the distance travelled of porcelain and or other parts of the equipment that potentially could cause serious injury.

The approach outlined in this document is consistent with that detailed in UKBP TP139 (Management of the Safety Risks to People from Equipment Retained in Service with an Abnormal Condition). In cases where it is impractical to apply the generic guidance presented here, a more detailed, site specific assessment should be undertaken in accordance with UKBP TP139 by the relevant asset specialist within Electricity Network Investment (ENI) Asset Engineering.