[1]How to Select Relays.—The following general information on relays, together with reference to the one line diagram, fig. 2,323, will be of interest and assistance in making a selection from the various relays previously described to meet the requirements of modern power house and sub-station layouts.
[1] NOTE.—As suggested by the General Electric Co.
Single pole relays are used on single phase and on balanced three phase circuits.
Double pole relays are used on ungrounded three phase and on quarter phase.
Fig. 2,324 to 2,329.—General Electric inverse time limit overload circuit closing relays. In this type of relay its mechanism is so designed that a delay or lapse of time in opening the circuit breaker after a predetermined condition of the circuit has been reached, depends on the flow of current, that is, if the current be great, the time will be small, and if the current be of a moderate value, the time will be correspondingly longer.
Triple pole relays are used on three phase grounded neutral and interconnected quarter-phase.
Circuit closing relays are recommended in all cases where a constant source of direct current is available for operating trip coils.
The conditions for which relays have been designed for power circuits may perhaps be best described, by considering a one line diagram from the generator end to the sub-station auxiliary machines and feeders.