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The light-load or friction adjustment of an energy meter compensates for

  • A.the friction of the bearings and register at small loads
  • B.the iron loss in the shunt magnet
  • C.the heating of the disc by eddy currents when the load is heavy
  • D.the effect of a low power factor on the phase of the shunt magnet flux

Answer: A

Friction is roughly constant while the driving torque falls with the load, so at five per cent of rated current it may be an appreciable fraction of the torque and the meter would run slow. A small extra torque, obtained from a shading loop near the shunt magnet, makes up for it.

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