A separately excited DC motor is energised from a 440 V, 50 Hz, 3 ϕ full converter. The input voltage to the motor for a firing angle of 45°, in volts, is:

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BHEL Engineer Trainee Electrical 2019 Paper

Answer 1

Concept:

The output voltage of a three-phase full converter is given by

\({V_0} = \frac{{3\sqrt 3 {V_{mp}}}}{\pi }\cos \alpha\)

V_mpis maximum supply phase voltage

α is firing angle

Calculation:

Given that, rms supply line voltage (V_rms) = 440 V

Maximum supply phase voltage \({V_{mp}} = \frac{{440\sqrt 2 }}{{\sqrt 3 }}\)

Firing angle (α) = 45°

\({V_0} = \frac{{3\sqrt 3 }}{\pi } \times \frac{{440\sqrt 2 }}{{\sqrt 3 }}\cos 45 = 420.16\;V\)