NEWS IN DEPTH
HSE safety alert says to check circuit breaker
lubrication and cleaning following explosion
The incorrect use and application of
lubrication on HV (high-voltage)
and LV (low-voltage) circuit
breakers could result in mal-operation
and increased risk of catastrophic
failure and downstream fire, according
to a safety notice from the Health
and Safety Executive. 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, BS 6423, BS 6626, BS
6867, and as prescribed in the manufacturer’s
instructions. In particular, the maintenance
procedure should ensure that the
manufacturer’s instructions on cleaning and
lubrication of the circuit breaker mechanism
are followed at appropriate intervals, including
the selection and application of the correctlyspecified
lubricants (products) for the task.
Photograph of the HV oil
circuit breaker taken after the
catastrophic failure, which
resulted in a fire and an explosion
within the substation
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 while retaining the original name.
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.
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 re-lubricate 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.
HSE said that it should be common
knowledge in the switchgear industry that the
incorrect use and application of lubrication
has been a major cause of mal-operation
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 multipurpose
lubricants for both cleaning and re-lubrication 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 two weeks
of application. The analysis concluded that for this reason,
multipurpose lubricants containing solvents (for example
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.
Duty-holders and specialist electrical contractors should
review their current maintenance procedures, HSE advises.
Winter 2021 www.operationsengineer.org.uk 15
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