Protective relays constantly monitor the power system to assure maximum continuity of electrical service with minimum danger to life and property. Protective relays are a form of insurance. Abnormalities are quickly recognized and action initiated to isolate faulted equipment. But, just like insurance, you have to make a tradeoff between the expense of insurance vs. the cost of the outcomes. And, since perfect continuity of service and maximum equipment protection are inconsistent goals, compromises are necessary and must be evaluated on the basis of comparative risks and costs.
