Operating requirements of the automatic network relay

This paper describes, in an elementary manner, the various relations between distribution system characteristics and the design characteristics of the relays which are used to provide automatic control for the so-called automatic, low-voltage, a-c. network distribution system. In the first part of the paper the general principles of operation of the relays and the limits of magnitude of the various actuating forces are discussed; in the latter part, the relations between distribution system characteristics and the phase angles' involved in the operation of the relays are described. It is shown that relays having simple watthour-meter characteristics are not fully applicable to all network systems of the automatic type, but are generally applicable to those having certain limited characteristics. Relay characteristics which would have practically universal application are described and a brief discussion as to the future trend of development is included.