Characteristics of protective relays

E. M. Hewlett
1912 Proceedings of the American Institute of Electrical Engineers  
The object of this paper is to describe the general character istics of protective relays necessary for the automatic and-selec tive action of circuit breaking and switching devices connected to electrical distributing systems. It is not my purpose to dis cuss or advocate any specific type or make of relay, but rather to bring before you the necessary characteristics and present a few recommendations for your consideration in selecting the proper type of relay for any particular service. The
more » ... cessful operation and control of electrical distributing systems, which are becoming more complicated each year, to gether with the rapid increase in the application of electrical power, present engineering problems in the design of proper pro tective apparatus which demand and deserve the most careful attention of designing engineers. In these days when so much depends on the continuity of electrical service, our protective apparatus-must be designed with this consideration in view* otherwise the service will be continually interrupted. The oil circuit breaker, the protective element of the distributing sys tem, should be permitted to lag sufficiently so that the short cir cuit current of the generator will reach a value which can be economically opened by the protective apparatus ; consequently a relay having selective action is necessary. On the other hand, the time limit relay should have a characteristic which will present such a rush of current as would result in the destruction of the cable and bus bar compartments. Variation in time in the op eration of a circuit breaker is sufficient in some cases to detetseaisue the particular switch which will be disconnected independent^ the action of the relay, consequently we should not endeavor to set 267
doi:10.1109/paiee.1912.6659630 fatcat:malkli6oebfy5f52ewf6rz3xfu