Design of an Overcurrent Protection Relay Based on Electronics Technology

Abstract

Protection relays are essential components in distribution networks that are used to protect the interphase faults and single-phase-to-ground faults. However, these relays do not assurance the protection due to the sharp growing short circuits. They may be the result of demanding more and more power usage by the commercial and residential users. Overcurrent relay (OCR) is the cost-effective and broadly used element in power system protection. In this paper, the design of an overcurrent relay in 0.18μm CMOS standard technology is performed for the protection of the 10-kilo-volts distribution system against the undesired currents. In this case, we have considered a time-reversed type relay where the operation time of the relay has a reverse proportion with its current. Firstly, crucial features of the relay are converted into digital data using electronic circuits including; encoder, analog to digital converter (ADC), multiplier, etc. In the next step, using an analog comparator leads to having the results of the comparison between the relay nominal-current and the actual line current. Finally, the value and the duration of the overcurrent are compared with the relay characteristics and the output results will ensure the circuit to continue the operation or not. Therefore, the proposed relay guarantees the protection of the system by overcurrent detection and cutting-off the system in the critical situations in a safe and fast way. Simulation results through Hspice can strongly prove the proper operation of the proposed overcurrent relay.