Improving the Reliability of Relay-Protection and Automatic Systems of Electric-Power Stations and Substations

Abstract

The main reasons for false (incorrect) triggering of microprocessor relay-protection systems are analyzed. Methods of increasing the reliability indicators of relay-automated systems are considered. Analysis of statistical data revealed that the probability of no-failure operation of microprocessor relay-protection systems is no lower than 0.998. Increasing the reliability indicators of microprocessor-protection systems does not require a revision of the Electrical Installation Rules, but requires using high-quality cable products with normalized technical characteristics and transition to a digital data-transfer format with a limited number of variables transmitted by one serial channel. The approximate upper and lower bounds of dependence of the cost of improving the reliability of microprocessor system are stated. For example, halving the amount of failures requires increasing the capital costs for electromagnetic protection by three to four times. Maintenance of the level of reliability of microprocessor system during operation is possible only during implementation of routine measures of evaluating the electromagnetic environment. Statistical data showed that the most likely cause of incorrect triggering of relay automation is atmospheric phenomena—lightnings and ensuing overvoltage. Therefore, at the stage of determination of the electromagnetic state, it is necessary to note the state of the earthing system it is most appropriate to carry out fault diagostics using the half-interval method taking into account the possibility of no-failure operation.