Modernization of relay systems

Relay systems used for the protection of power transmission networks are now available which are greatly superior to those in use some 5 years ago. The principal change has been the development of the high speed relay, the operating time of which may be as low as one cycle or less on a 60 cycle system. Modernization of existing relay systems frequently may be accomplished by the addition of the new relays to the present relay scheme, thereby avoiding the cost of an entirely new relay system. High speed relays, especially when used with high speed circuit breakers, result in reduction of damage at stations and on lines, and give improved system stability and operation; reduction of outages on equipment of industrial customers has been an important advantage. This paper on modernization of relay systems is presented under the sponsorship of the relay subcommittee of the A.I.E.E. committee on protective devices.