Surges power capacitors

All electrical equipment are designed for a specific BIL, as indicated in Tables 11.6, 13.2, 14.1, and 32.1(A) for motors, switchgears and bus systems respectively, and Tables 13.2 and 13.3 for the main power system (line clearances and insulators). If the actual severity of a prospective surge, i.e. its amplitude and/or rise time or both, is expected to be higher than these levels (higher amplitude and lower rise time) the same must be damped to a safe level, with the use of surge arresters, surge capacitors or both as discussed later. 

A surge capacitor offers a near-open circuit during normal operation (at or near the power frequencies) and a near-short-circuit to the arriving surges at surge frequencies, while the inductance of the motor windings (<> will... 

A possible location for an additional X-cap is directly on the prongs of the inlet socket (at the entrance to the power supply). We remember that in this position any line-to-line capacitor will be exposed to a huge current surge at power-up, and could degrade, if not fail immediately. So if this X-cap position seems to be the last resort, it should at least be made as small as possible (typically 0.047 iF to 0.1 < I ). Or we can try ceramic capacitors in this position (approved ceramic X-caps or Y-caps should be tried here). 

The principle equipment generally installed in a distribution substation are power transformers, oil or air circuit breakers, voltage regulators, protective relays, air break and disconnect switches, surge arresters, measuring instruments, and in some instances, storage batteries and capacitors. 

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