| 摘要 |
In the case of operating a three-phase asynchronous motor in the oversynchronous rotational speed range, the motor exerts a braking torque. If the three-phase asynchronous motor has two speed stages, this braking torque produced on switching over from the higher rotational speed to the lower rotational speed can cause a "switching shock" which can be dangerous. The switching shock is reduced if one phase winding of the stator winding is separated from the mains. Switching back of the phase winding is carried out in dependence on the voltage between the phase winding switched off and its phase, which voltage is lower in the case of synchronous rotational speed than in the case of neighbouring rotational speeds. The method is used in the case of pole-switching (pole-changing) motors or separate high-speed and micro-sped motors which are, for example, components of hoisting machines. <IMAGE>
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