ABSTRACT
Protective relaying has been called an "art" and also a "science". This is so because there is a judgment involved in making selections, which require compromises between conflicting objectives, such as maximum protection, reliability, fast fault clearance times, economics, and selectivity. Protective relaying must be considered alongside the design of power systems, large or small. The logic of protective relaying looks at a complex distribution system as an integration of subsystems. A protection system must operate so as to isolate the faulty section only. In a radial distribution system, which is a common system configuration in the industrial power distribution systems, inverse time overcurrent relays are used as the primary protection devices. Fault damage to the system components and the stability between synchronous machines and interconnected systems are related to the speed of operation of the protective systems. Dependability and security are the measures of reliability.
