A NEW METHOD FOR DEVELOPING AND TESTING OF COMPUTER RELAYING ALGORITHMS FOR POWER SYSTEM PROTECTIONS

Abstract

Problems associated with the tests of protective devices have been of interest to power system protection engineers for many years. Conventional test methods include artificial short-circuits on the primary power network, which is a costly and dangerous method, or the secondary tests, when appropriate voltage and current signals have to be injected to the protective device. The problem of this second method is the modelling of the pri- mary transient phenomena with considerable power. The microprocessor based protection represents an advanced technology in the power systems. Their development and testing needs an advanced technology as well. The transient signals are calculated off-line by a computer simulation, then the results are converted to analogue signal and put into the relay's input. In this way the new protection can be tested using transient signals, but special power amplifiers are needed as well. Our new method uses the communica- tion capability of the computer relay. The transient signals are computed off line by a special EMTP program, then these numerical values are sent directly to the CPU of the protection, passing by the analogue circuits using the standard RS232 connection. Our system leads to a general improvement in the development process of new protection's algorithms and it helps efficiently in teaching power system transients and power system protection as well. The use of the new method is illustrated by practical examples of a digital, transformers differential protection.