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The unbalanced set of 3-phase voltages causes ________(a) Positive sequence current(b) Negative sequence current(c) Zero sequence current(d) Half sequence currentThe question was asked in unit test.Origin of the question is Induction Motors topic in section Braking of DC Motors & Induction Motors of Electric Drives

Answer»

Correct choice is (b) Negative sequence CURRENT

Explanation: The unbalanced set of 3-phase voltages causes a negative sequence current. The magnetic FIELD generated due to negative sequence current is in the opposite direction to the FUNDAMENTAL magnetic field. This induces double the FREQUENCY current in the rotor side which causes overheating of the motor.



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