Health and Safety Executive issues safety notice regarding the lubrication of circuit breakers

The incorrect use and application of lubrication on HV and LV circuit breakers resulting in mal-operation and increased risk of catastrophic failure and downstream fire. Duty-holders and Specialist Electrical Contractors should ensure that their maintenance procedures associated with cleaning and lubrication of HV and LV circuit breakers meet with the requirements defined in HSG 230[3], BS 6423[4], BS 6626[5], BS 6867[6] and as prescribed in the manufacturer’s instructions. In particular, the maintenance procedure should ensure that the manufacturer instructions on cleaning and lubrication of the circuit breaker mechanism are followed at appropriate intervals, including the selection and application of the correctly specified lubricants (products) for the task.

Investigation into an explosion of a HV circuit breaker indicated that recently carried out maintenance may have been a causal factor. The incident resulted in catastrophic failure of the HV circuit breaker leading to fire / explosion and could have resulted in fatal injuries. Maintenance of HV and LV circuit breakers typically involves both the cleaning and lubricating of the operating mechanism. The HSE investigation found that the same physical product was used for both maintenance activities, but evidence shows the product was in fact only suitable for cleaning and NOT lubrication. This situation may have arisen because of the availability of different products, (for different purposes), within the same product range, or changes to the products composition over time whilst retaining the original name. It is essential that the correct product is used for each task.

Photograph of the HV oil circuit breaker taken after the catastrophic failure, which resulted in fire and explosion within the substation – Image via HSE

HV and LV circuit breaker mechanisms are required to operate at high speed to disconnect electrical faults with a high degree of reliability from the associated electrical system. To ensure the required performance is retained it is vital that the circuit breaker operating mechanisms are functionally checked and maintained periodically as per the requirements defined in relevant good practice HSG230[3], BS 6423[4], BS 6626[5] and, BS 6867[6] and as prescribed in the original manufacturer’s instructions.

If during functional testing (including circuit breaker timing tests) or during periodic planned preventative maintenance it is observed that the mechanism is slow to operate, it is good practice to relubricate the mechanism, adhering to the recommendations given in the manufacturer’s instructions. During the planning stage, this will involve identifying the correct type of lubrication to be applied to different parts of the mechanism and how it should be applied. In extreme cases, where the circuit breaker mechanisms are observed to be sticking due to old, congealed lubricant, it is common practice to apply a cleaning product to remove this prior to re-lubrication. Care should be taken to ensure that the cleaning products are compatible with the circuit breaker following the recommended procedure given in the manufacturer’s instructions before reapplying the manufacturer recommended lubricants.

It should be common knowledge in the switchgear industry that the incorrect use and application of lubrication has been a major cause of maloperation in switchgear and can lead to very serious consequences. However, observations made during several recent routine planned inspections relating to the maintenance of circuit breakers together with the findings from a recent HSE investigation – where an employee marginally escaped serious personal injury when an HV circuit catastrophically failed – has highlighted that this information may no longer be common knowledge. HSE routine inspections and investigation found evidence that some HV and LV specialist electrical maintenance contractors and end users commonly use aerosol based multi-purpose lubricants for BOTH cleaning and relubrication tasks.

The recent HSE investigation into the failed HV circuit breaker concluded that ‘stiction’ in the failed circuit breaker may have been a result of an incorrect aerosol based multipurpose lubricant being applied to the circuit breaker mechanism. This happened even though the circuit breaker had been maintained less than three months prior to the incident and was reported to be operating satisfactorily. Independent forensic analysis work conducted during the investigation showed that the multipurpose lubricant used during the maintenance of the failed circuit breaker prior to the incident, evaporated by 75% of its original weight within 2 weeks of application. The analysis concluded that for this reason, multipurpose lubricants containing solvents (e.g. white spirit) are unsuitable for use as a lubricant of this type of HV and LV switchgear.

In addition, historical research by other organisations recommended that hydrocarbon sprays or solvents should NOT be used on circuit breaker mechanisms.

You can read the full safety notice here – https://www.hse.gov.uk/safetybulletins/lubrication-circuit-breakers.htm

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