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Resistance-capacitance phase protection circuit

2015-03-02 16:39  
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Resistance-capacitance phase protection circuit
The circuit shown in Figure uses negative sequence voltage generated by unbalanced three-phase power for phase-failure protection. When the three-phase power is symmetric and line voltage has mutual lag 120°electrical angle, the voltage across the relay KV voltage is 0V, so KV has no action. When the three-phase power loses a phase, the voltage is applied to the ends of the coil, KV pulls in, and its normally open contact action to turn on KM2 coil loop, then the normally closed contact KM2 action, KM1 cuts the power supply of motor M.