Relay protection of tapped transmission lines

The war, with its attendant shortage of critical materials, has led to a considerable increase in the number of tapped lines. This paper deals with the method of protecting circuits of this kind under the three headings: 1. Pilot-wire protection, a-c and d-c schemes. 2. Carrier-current protection. 3. Other protective schemes. Directional overcurrent or network. Distance type. Three-terminal lines are classified into three types with regard to other system connections between the terminals connected by the line in question. These are further classified as to power sources to aid in analyzing limiting conditions for relay applications. Typical operating characteristics of a-c pilot-wire equipment for three-terminal lines are shown. In general in dealing with pilot-wire, carrier, and other types of protection, those problems peculiar to application on three-terminal lines are analyzed and methods given for solving some of the more troublesome problems.