Ans. From 125 to 250 volts.
Ques. Where is this current usually obtained?
Ans. From a storage battery, or from the exciter.
Ques. For what current are the contacts ordinarily designed?
Ans. About 10 amperes.
Figs. 2,292 to 2,300.—General Electric alternating current, instantaneous overload circuit closing relays, covers removed. The function of a circuit closing relay is to close an electrical circuit, usually direct current, through a trip coil on an oil switch or circuit breaker, or it may short circuit a low voltage release coil, and thereby open the oil switch or circuit breaker on occurrence of the condition upon which the relay is designed to operate. Direct current at 125 or 250 volts taken from exciter bus bars or storage battery system is generally used for the tripping circuit. Circuit closing contacts have a cone shaped central element of carbon or metal which makes contact with flexible contact fingers symmetrically arranged above the cone. These contacts will make and break a circuit of 10 amperes at 125 volts without the use of auxiliary circuit opening switches. Relays are made with two or three contacts for connecting one side of a direct current circuit through one or two separate circuits, or trip coils respectively, to the side of opposite polarity. Usually only two contacts are required. Where two or more trip coils are used, which may not be connected permanently in parallel, the three contact relays are selected and in some cases four contacts furnished.
Primary and Secondary Relays.—Primary relays are sometimes called series relays as they have the current coils connected directly in series with the line, both on high and low tension circuits.
Secondary relays receive their current supply from the secondary circuits of current transformers. Alternating current relays connected to secondary of pressure transformers and relays with both current and pressure windings are included in this class.
Ques. What is the usual winding of the coils?