Transformer reliability ranges between fair and good
for the substations evaluated. In all 4 cases, we find
circuit breaker health to be of concern. A detailed
investigation is required as the next step in order to
determine normal ageing, or areas of risk for the
circuit breakers.
In sample B, one of the CB routine test results was not
available. If one assumed the same performance for
this breaker as the others, the substation PHI score
increases by 30%, but the substation PHI still remains
in the Alarm zone.
For sample C, the Transformer PHI is skewed. The
water content value must be evaluated in conjunction
with the temperature at the time of sampling i.e. we
expect the water content to be “higher” for lower
operating temperatures, typically observed with the
lighter loaded transformers. For sample C, a capex
project has already been approved for replacement of
the circuit breaker. The target completion date can
now be influenced based on the PHI evaluation.
In the last sample, D, the same findings were made for
the WC as in the previous case for the transformers.
One of the installed seven circuit breakers, needs
attention however, whilst the rest are in the alarm
stage, indicating on-set of the wear-out stage. The
circuit breakers are 25 years old