Service Supply Line Protection

The important considerations involved in the protection of various electrical supply line circuits to consumer loads are presented. Supply system disturbances are first reviewed as to type, duration, magnitude, and cause. The sensitivity of various kinds of consumer loads are listed and analyzed. Methods of minimizing the effect of power supply system disturbances are given. These corrective measures include proper selection of 1) power equipment and switching devices, 2) control circuit modifications, and 3) methods of service restoration. Types of available protective relay systems are grouped by location and six typical electrical supply system protective schemes are described and illustrated.