Patent ID: 9343895
Filing Date: 2016-05-17
CPC Classification: H02H

Claim Text:
1. A self powered protection relay for providing electrical protection in an electrical system by measurement of current in at least one phase line in a medium voltage power line, and generation of a trip signal on detection of an overcurrent and earth fault condition in the medium voltage power line to operate a circuit breaker for electrical protection, the self powered protection relay comprising: a power supply module for supplying power to the self powered protection relay from the at least one phase line that the self-powered relay is to measure for providing electrical protection in the electrical system; and a current processing module for measuring and evaluating current in at least one phase line to generate a trip signal, wherein the current processing module is configured to provide inrush current suppression to block detection of an earth fault condition during an inrush condition, wherein the current processing module determines an inrush condition in at least one phase line based on one or more states of: a) a current signal not being in a steady state condition; b) a value of current being more than approximately 10% of a current sensor nominal value; c) a value of current being below a preset fault threshold value; and d) a harmonic content in a current signal at a second harmonic as a ratio to harmonic content at a fundamental frequency exceeds a preset harmonic ratio threshold; and wherein the current processing module is configured for determining the steady state condition based on one or more states of: a) a value of current at the fundamental frequency falls below approximately 10% of a current sensor nominal value; and b) a value of current at the fundamental frequency falls in a range of approximately 95% to 105% of a value of current at the fundamental frequency in a previous period when measured for at least one period.