Lessons learned: Catastrophic failure and explosion of HV circuit breaker

The incident

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. As explained, maintenance of HV and LV circuit breakers typically involves both the cleaning and lubricating of the operating mechanism.

Findings

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.

What was the cause?

• ‘stiction’ in the failed circuit breaker may have been a result of an incorrect aerosol based multi-purpose lubricant being used on the circuit breaker;
• Independent forensic analysis 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, multi-purpose lubricants containing solvents (e.g. white spirit) are unsuitable for use as a lubricant of this type of HV and LV switchgear.

Actions

• Review maintenance procedures associated with cleaning and lubrication of HV and LV circuit breakers;
• Check that the maintenance procedure ensures 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 (typically this will be two separate types of product).