*Article* **Development of Railway Protective Relay Simulator for Real-Time Applications**

#### **Joorak Kim, Gyu-Jung Cho and Jaewon Kim \***

Korea Railroad Research Institute, Uiwang 16105, Korea; jrkim@krri.re.kr (J.K.); gjcho@krri.re.kr (G.-J.C.) **\*** Correspondence: youngkjw@krri.re.kr; Tel.: +82-31-460-5549

Received: 20 November 2019; Accepted: 17 December 2019; Published: 25 December 2019

**Abstract:** Electric railways use a single-phase system, with the line comprising a trolley wire (TF) that supplies power to the load with a neutral wire and an autotransformer (AF) feeder to absorb the return current of the rail. Testing the performance of the protective relay that detects the fault of the traction power-supply system (TPSS) and operates the circuit breaker is very important. Until now, the performance test of protective relays for the TPSS has been conducted via a simple-steady test or using an expensive real-time simulator. However, under a fast-moving environment in which the load consumes a large amount of power, the protective relay must always detect faults and operate properly. This paper proposes a digital simulator that enables the dynamic testing of protective relays without using any steady test and expensive real-time simulators. This simulator includes both external waveform import and internal waveform generation functions. Users can test the operation of the protective relay by entering the waveform generated externally or internally into the protective relay. Additionally, it has the ability to monitor the operating protection elements and pickup time when the protective relay detects a fault and orders the circuit breaker trip.

**Keywords:** traction power-supply system; protective relay; digital simulator; monitoring and controlling system; railway
