Zero sequence voltage off-phase protection circuit

Published:2011/7/6 5:01:00 Author:John | Keyword: off-phase protection | From:SeekIC

As shown in the figure, when the motor is within normal operation, the three-phase power supply is connected to three capacitors Y with the equal capacitance. Then potential of its contact E is 0V and the secondary side of transformer T2 is with no output voltage. As a result, when the VT is turned off, the K is released and its normally closing contacts are normally closed. And KM coils work properly. When any phase of the three-phase power supply is off, contact E values several volts due to the unbalanced three-phase. The voltage is gone through the transformer T2, VD1 rectifier, C4 and C5 filters, VD2 regulator, C6 and delay resistor R1. Afterwards, the voltage is added to the VT base to induct VT. K acts to cut the normally closing contacts of K. The KM circuit is cut off and the motor M stops working without electricity.



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