The condition monitoring records the operation of both compressed air pumps installed for all 132-kV circuit breakers in the substation. The pumps normally turn on around 21:00:34.46 and cut off around 21:13:34.64 with an average duration of 13 minutes. If there is any deviation from this set of data, it may imply a serious hidden fault with a circuit breaker. When only a single auxiliary contact is available, it is not possible to obtain the three-phase traveling data as it was at Castle Peak.

Another type of circuit breaker in Tsz Wan Shan is used for reactor switching, but auxiliary contacts are not available for this type of circuit breaker. Therefore, a new method was developed to measure the operating time of these circuit breakers based on current waveforms. The current waveforms from closing and tripping a typical 132-kV circuit breaker used to switch an 80-MVA reactor. From these figures, it is obvious that the closing time for the circuit breaker is 125 ms while the trip time is 50 ms. This method is particularly useful for measuring the time discrepancy in the travelling of the three phases when auxiliary contacts are not available. The method offers an additional advantage because it measures actual current waveforms.