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When analysing databases, especially from complex recorders that capture the waveforms and disturbances, it saves an incredible amount of time recognising events with the same characteristics.
The two examples above show the same style of current curve at the time of the fault occurring. Such "signatures", the fact that the fault happens at exactly the same point on the cycle, are undoubtedly tell-tale of being solid-state, or even microprocessor controlled switching that is not functioning properly. This was a phase locked UPS that lost lock when a mains borne signalling system became active. But signatures don't only exhibit themselves as having the same cycle patterns. They can disguise themselves as seen in the following example. These two events above were as far as 3 days apart and could easily have been accepted as two completely separate transients, substantiated by the fact that they happened on two different points on the cycle. It is when they are compared with each other the similarity becomes almost frighteningly obvious. This fault happened at exactly the same point on the same piece of equipment. In this above example the energy involved in the fault is dependent on the point of the cycle at which the fault occured. This was a motor speed controller that would accidentally switch a thyristor on at the wrong moment, and at times with catastrophic results - the thyristor was permanently damaged and would have to be replaced.
© 22.09.01 |
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