This section considers the requirements for protection of the complete drive and motor system from the effects of faults and voltage transients. As in other chapters, much of the underlying philosophy is common to all electrical power installations and it is not the purpose to repeat it here. There are some special considerations in relation to drive systems, and these are addressed. The most common form of circuit protection is the fuse, followed by various forms of circuit breaker. Standard industrial fuses and circuit breakers are designed to protect the distribution circuits from the effects both of long-term overloads and of short circuits. In the case of a circuit breaker there are separate actuators (thermal and magnetic) for these two functions, whereas the thermal design of the fuse is adjusted to effectively model the thermal behaviour of the cable in both respects. In all cases the device must also carry predictable safe peak currents such as the starting current of direct-on-line (DOL) motors without undue deterioration. It is difficult to protect semiconductor devices from damage caused by a short circuit using a circuit breaker, as the response time needs to be very rapid, so the following account refers primarily to fuses. It should be understood, however, that in some cases, especially at the lower power levels, a circuit breaker may be able to fulfil the function equally well.

Inspec keywords: machine protection; electric fuses; circuit breakers; short-circuit currents; transients; motor drives

Other keywords: industrial fuse; electrical power installation; faults; safe peak current; semiconductor device protection; DOL motor starting current; drive system protection; direct-on-line motor starting current; short circuit protection; distribution circuit protection; voltage transient; motor system protection; circuit breaker; power supply infrastructure

Subjects: Drives