Damage risks - fault currents and arcs

In power supply networks, fault currents cause arcs with the release of a considerable amount of energy. An AC system with period T, peak current Iol 

overhaul and rebuilding costs combined with production losses come up to a multiple of the capital expended for the switchgear. 

Similar considerations can be made for semiconductors in rectifiers and frequency convertors. The maximum load integral for semiconductors in power equipment can be assumed with values starting from 103A2s up to (and exceeding) 107A2s. 

Even in times near to the zero passage of a short-circuit current these values may be transgressed. As a good approximation, a sine-shaped current can be represented by linearity near its zero passage. 

With I0 = 30 kA, the maximum load integral follows with 3 104A2s after 1 ms and with 2.4 105 A2s after 2 ms only. This fact indicates that even in the vicinity of zero passage of a short-circuit current semiconductors with maximum rms on-state currents in the range 100 A to 800 A are endangered after a few milliseconds only. 

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