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线路如图所示的一台卷扬机，一次突然发现，无论按动提升按钮还是下降按钮，卷扬机均下降，检查控制线路和负载都正常。再仔细检查才发现，提升按钮接触器 2C的 B相触头接触不良，使电动机实际得到的只是两相电源，异步电动机断掉一相后是不能起动的，但在卷扬机中，通常料斗及
A winch, as shown in the picture, suddenly discovers that the winch is lowered no matter whether the push button or the push button is pressed, and the control circuit and load are all normal. Careful examination revealed that the contacts of the B contact of the push button contactor 2C are not properly connected, so that the motor actually obtains only two-phase power. The asynchronous motor can not be started after one phase is cut off. However, in the winch, usually the hopper and