| 摘要 |
The invention relates to an electrical protection device for monitoring especially converter-supplied asynchronous motors. It is intended to create a protection device which reliably detects all the disturbance cases throughout the speed range which are required to disconnect the motor, irrespective of whether it is used with mains-supplied or converter-supplied machines, and, if such disturbances occur, causes the disconnection of the motor. This is achieved by means of a circuit which generates an electrical actual signal corresponding to the root-mean-square value of the respective phase current for each phase of the asynchronous motor, a first comparator circuit, in which the electrical actual signals are compared with a limiting value which can be preset, and a first disconnection signal is generated when at least one actual signal exceeds the limiting value, a second comparator circuit which compares the actual signals with one another and generates a second disconnection signal when the actual signals deviate from one another by more than a difference which can be preset, by means of a third comparator circuit which, in the frequency band of the phase current below a frequency limit which can be preset tests the actual voltage applied in each case to the motor for correspondence to the nominal voltage of the converter associated with the instantaneous frequency and generates a third disconnection signal if the actual voltage is less than the nominal voltage by a magnitude difference which can be preset, and by a device for disconnecting the motor when a disconnection signal occurs.
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