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A current transformer is tested at several fractions of rated current because its

  • A.phase angle error reverses in sign above rated current
  • B.burden alters as the secondary current is raised
  • C.errors vary considerably with the current
  • D.core temperature changes as the current is increased

Answer: C

The exciting current is not proportional to the primary current, so the error expressed as a percentage is quite different at ten per cent of rated current from what it is at full load. Accuracy classes accordingly state limits at 5, 20, 100 and 120 per cent of rated current.

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