A Study on Circuit Topology for Open-Phase Fault Detection of 3-Phase Motor Control Panel

When a open-phase occurs in a 3-phase power system using a 3-phase motor, an unbalanced current applies to the power system, results in a fire due to overcurrent in the motor coil and great damage to the power system. The conventional open-phase detector of the 3-phase motor is mainly used with a THR (Thermal over-current Relay) or an EMPR (Electronic Motor Protection Relay). However, since these detector have the principle of detecting open-phase faults by sensing currents in 3-phase lines, it causes malfunction from the surge or external noise currents, and it is difficult to install the detectors. In order to solve these problems, this paper proposes a method and circuit topology for detecting the open-phase faults by detecting 3-phase voltages rather than detecting 3-phase currents. The proposed open-phase detection circuit is designed in a structure using the output voltage waveform and magnitude of the 3-phase half-wave rectification circuit. Since the proposed detector is designed with a voltage type, there are no malfunctions from the surge or external noise currents and the detector is simple and compact, giving ease of installation. Copyright © The Korean Institute of Electrical Engineers.