Differential protection switching method from starting stage to operation stage of high-power synchronous motor

The invention belongs to the field of motors, and particularly relates to a differential protection switching method from a starting stage to an operation stage of a high-power synchronous motor. According to the technical scheme, when it is monitored that a main transformer circuit is switched off and a variable frequency starting circuit is switched on, differential protection is controlled to quit protection of the high-power synchronous motor. And when it is monitored that the frequency conversion starting circuit is closed, after a first time T is delayed, the differential protection is controlled to be put into protection on the high-power synchronous motor. And the main transformer circuit, the frequency conversion starting circuit and the differential protection are also electrically connected with a PLC (Programmable Logic Controller). 本发明属于电动机领域，具体涉及一种大功率同步电机启动至运行阶段的差动保护投退方法；技术方案包括：当监测到主变电路断开，变频启动电路闭合时，控制所述差动保护退出对所述大功率同步电机的保护。当监测到变频启动电路闭合，延时第一时间T后，控制所述差动保护投入对所述大功率同步电机的保护。所述主变电路、所述变频启动电路和所述差动保护还与PLC电