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Case Study: opmal funconal tesng

interval for 11kV circuit breakers
Problem descripon: What is the opmal funconal tesng interval for a
11kV circuit breaker?
The SALVO Process (www.SALVOproject.org)
provides a storyboard for evalua ng
different asset interven ons. For funconal tes ng strategies, it introduces the
DST Inspec on Evaluator tool, to enable
the storyboard–guided considera on and
quan fica on of:
Risks of different circuit breaker failures
modes

Degrada on mechanisms, with probability pa.erns and possible consequences as injury, damage to assets,
environmental impact and down me
to the customer.

Random damage and introduced risks,
including those associated with the
tes ng ac vity.

Direct and indirect costs, quality and reliability of tesng and methods

Switching costs, labour and travel
me/costs.

Outage/down me impacts of isola ng
the breaker for the test, including risk
of secondary problems and period of
reduced standby flexibility).

Results and benefits:
The study determined the opmal
tesng strategy, including sensivity analysis to uncertain data. It revealed the opmal interval to be 36
months. Compared to the present
interval of 12 months, the benefit of
moving 5000 circuit breakers to 36
months is c.£162,000 per year.

Circuit breakers perform a cri cal role in an electrical supply network. If they are in a failed state (which might not
be evident to the opera onal personnel at the me), major incidents can occur if their protec ve func on is not
available. So a cost-effec ve tes ng programme is needed to find and fix any failures.
The organisa on has 5000
circuit breakers across their
network, currently tested
every year. By using the
SALVO process and the DST
Inspec on Evaluator tool,
this strategy was shown to
be inappropriate.

The structured SALVO
process, supported by
instant cost/risk modelling, revealed the op mal tes ng interval to
be 6-yearly (using ‘most
likely’ assump ons).

However DST enables data uncertainty to be considered too,
and this showed that different assump ons could jus fy a
wide range of tes ng intervals, but a 3-yearly frequency is an
appropriate strategy (best
value mix of costs and
risks) in all possible interpretaons. This provides
management confidence in
implemen ng the recommended strategy, with
clear audit trail and demonstra on of why the strategy
is appropriate.

♦ State-of-the-art analy cal so=ware to evaluate the cost. opera ons. with clear ‘storyboard’ checklist to ensure all factors are considered Disciplined process to draw out and quan fy the knowledge of cross-disciplined teams and subject ma.Analysing funconal tesng of protecve devices and stand-by systems DST Inspec on Evaluator was developed as part of the interna onal SALVO project to guide and support the analysis of func onal tes ng and inspec ons of assets subject to hidden failure modes. and iden fy the op mal strategy. a formal decisionrecording stage ensures capture of the op mal strategy.com www. It needed just 2 hours to build a ‘base case’ model of the risks and costs and opera onal op ons available. maintenance and process safety personnel.decisionsuppor. For further informaon about DST Inspecon Evaluator. It provides: A structured logic. ♦ ♦ This case involved a small team comprising inspectors.ools. showing the best strategy to minimise the impact of this uncertainty. the implementa on ac ons and audit trail for why the tes ng interval is correct. Finally.er experts. please contact: Decision Support Tools Ltd. Hampshire RG 20 4SW Tel: +44 (0)1635 299200 www. Prince Henry House Kingsclere Business Park. inspec ons or engineering projects that occur across the network.org .SALVOproject. This stage is facilitated by another part of the SALVO process. it also shows the ‘cost of compliance’ compared to the cost/risk op mum. If there are mandatory requirements. and the DST Schedule Op mizer tool (which finds the op mal shutdown/outage and work bundling opportuni es for compe ng priori es and constrained resources or budgets). Sensi vity analysis then automa cally explored the effects of data uncertainty. and the SALVO processes. risk and op mal mings of inspec ons or tes ng strategies. Further work: The next stage for such studies is considera on of the op mal bundling of these func onal tests with other planned maintenance.