The six ways to ensure improper operation of microprocessor relays

At the 44th Annual Conference for Protective Relay Engineers in 1991, Walt Elmore presented the paper “Ways to Assure the Improper Operation of Transformer Differential Relays.” This paper applies the same approach to microprocessor relays. Relay designers work very hard to develop microprocessor relays that will be secure and dependable. However, a considerable amount of background and experience is required to apply them correctly. There is a limited number of correct ways to connect and apply a microprocessor relay and literally hundreds of ways to connect them improperly. Wrong connections or applications generally manifest themselves in an undesired trip or failure to trip. Often, unfortunately, this doesn't happen on first energization but rather during a fault when proper operation is most needed or during load periods when false operations are to be avoided. The six ways to ensure improper operation of microprocessor relays are presented with examples of each. The six ways are: 1. Fail to consider how the relay is set. 2. Fail to consider how the relay acts. 3. Fail to consider how the relay measures the power system. 4. Fail to consider how the relay operates the control system. 5. Fail to consider how the power system acts. 6. Fail to consider how the power system is operated. Applications of the Six Ways to design, testing and troubleshooting are discussed.