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Armature resistance control of speed is little used because it

  • A.wastes energy in the added resistance
  • B.cannot reduce the speed of the machine at all below its no-load value
  • C.requires a fully controlled rectifier to be provided as well
  • D.raises the speed above the base value rather than reducing it

Answer: A

The resistance drops voltage and dissipates it as heat, so efficiency falls in proportion to the speed reduction, and the speed also becomes very sensitive to load. It survives only in simple traction and crane starters.

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