Regulative Relays.—This class of relay is used to control the condition of a main circuit through control devices operated by a secondary circuit.
Ques. For what service are relays of this class employed?
Ans. They are used as feeder circuit or generator regulators.
Ques. How do they differ from protective relays?
Ans. They have differentially arranged contacts, that is to say, arranged for contact on either side of a central or normal position.
Fig. 2,280.—Diagram showing a railway synchronous converter protected by a single pole overload circuit breaker with low voltage release attachment and bell alarm switch. The low voltage attachment trips the breaker on failure of direct current voltage also when speed limit device closes. Internal troubles are taken care of by the alternating current automatic devices (not shown).
Communicative Relays.—These are used for signalling in a great variety of ways for indicating the position of switching apparatus or predetermining the condition of electric circuits.