Video: Circuit breakers and switchgear: what six technical webinars teach

Video transcript

Six technical webinars on circuit breakers and switchgear, summarised. What breaks, what conventional maintenance misses, and what a continuous monitor actually adds. Start with the reason any of this matters. Circuit breakers are by far the largest single contributor to substation events, and a breaker that fails to open, or is merely slow, leaves everything behind it exposed to the fault current. And when they do fail, the cause is overwhelmingly mechanical.

In the industry survey quoted across these sessions, mechanical problems account for between 83 and 90% of the reported problems, at every voltage class. The sessions are blunt about why cyclic maintenance misses these. The problems develop between the intervals, and several of them are invisible to a test that requires taking the breaker out of service. The offline tests themselves have limits worth knowing. Contact resistance, for instance, does not tell you about contact wear at all, because the arcing contacts are not the ones being measured.

Online, the measurement at the centre of everything is the trip coil current. Every bend in it is a piece of the mechanism moving, and at a 128 samples per cycle it is resolved to the millisecond. And the diagnosis is a comparison, not a threshold. When lubrication dries out, the first half of the waveform is unchanged and everything after the latch arrives late. The sessions add a detail worth remembering: operate that breaker a second time and the interrupting time improves,

which is itself the signature of a lubrication problem rather than a latch one. A question that comes up in every session: the protective relay already records the trip, so why add anything? Because the relay tells you about the fault, and the monitor tells you about the breaker. From each capture come the numbers a breaker is actually judged on. Gas gets a session of its own, and the argument against the gauge is simple. A mechanical gauge or a density switch needs somebody to look at it,

and only alarms once a significant amount of gas has already gone. And when the gas is tested rather than merely measured, the sessions set out what the laboratory work is for. Finally, switchgear, where the failure mode changes. Here it is not the mechanism but the insulation, and the measurement that finds it is partial discharge. If there is one thread running through all 6 sessions, it is this. Breaker and switchgear monitoring, from Amperis.