Novel microprocessor based negative phase sequence relay and meter

Microprocessor application in relaying and condition monitoring technology is becoming increasingly popular. In this paper, a novel microprocessor based negative phase sequence (NPS) current detector for motor condition monitoring and relaying for motor/generator protection is developed. The proposed meter eliminates the need of a negative phase sequence filter and does not require complicated digital signal processing techniques. Instead it uses a phase sensitive rectifier. A prototype based on Intel's 8085 A microprocessor was built and tested. Complete circuitry, main and interrupt software flowcharts are provided. Results show the proposed NPS relay and meter can provide a high degree of accuracy and satisfactory results.