我矿有１３台ＷＫ－４Ｂ挖掘机，其空压机电机及通风机电机常因缺相而烧毁。原设计空压机电机控制原理如图１。 电动机运行中保护它的是热继电器。在某种程度上，热继电器对电动机过载能起一定的保护，但动作迟缓。特别是对于电源缺相更是灵敏度低，电动机很容易烧损。 １改进 Mine mine has 13 WK-4B excavators, the air compressor motor and fan motor often due to lack of phase and burned. The original design of air compressor motor control principle shown in Figure 1. It is a thermal relay that protects the motor during operation. To some extent, thermal relays provide some protection against motor overload, but are slow to act. Especially for the power phase loss is less sensitive, the motor is easy to burn. 1 improvement