phase angle relay.
相角继电器

phase angle measuring relay
相角测量继电器

phase sequence voltage relay
相序电压继电器

arbitray phase angle power relay
有功无功功率继电器

Medium power single phase A.C. Solid state relay
单相交流固态继电器

Improvement of electronic starting relay of electric locomotive phase splitter
电力机车电子式劈相机起动继电器的改进设计

RESEARCH ON FAULT PHASE SELECTOR OF PROTECTIVE RELAY FOR DOUBLE CIRCUIT LINES ON THE SAME TOWER
同杆并架双回线保护选相元件研究

When internal fault occurs, the phase angle difference of two end currents is small and the restraint coefficient is small, so the sensitiveness of relay is high.
内部故障时两侧电流相位差小, 则制动系数小, 保护灵敏度高。