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The power factor of a phase-controlled rectifier drive at low speed is

  • A.poor, because the firing angle is large
  • B.excellent, because the current drawn from the supply is small
  • C.unity, since the load is essentially resistive at low speed
  • D.leading, because the converter supplies reactive power to the network

Answer: A

Delaying the firing displaces the current from the voltage, so the displacement factor falls as the cosine of the angle. A drive spending its life at low speed therefore loads the supply with reactive current as well as harmonics.

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