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Which type of test is NOT included in DC motor maintenance and repair?
1. Load test of motor
2. Reviewing the service history
3. Brush and commutator maintenance
4. Bearings and lubrication

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Correct Answer - Option 3 : Brush and commutator maintenance

The correct answer is 'Brush and commutator maintenance test is NOT included in DC motor maintenance and repair'.

Field test for series motor:

  • This test is applicable to two similar series motor.
  • One of the machines is run as a generator while the other as a motor.
  • Therefore input power is only losses in the machines.
  • Gives efficiency of DC series machine.

 

Hopkinson’s or Regenerative or Back To Back Test:

  • Two identical DC shunt machines are coupled mechanically and tested.
  • One of the machines is run as a generator while the other as a motor.
  • Therefore input power is only losses in the machines.
  • Performed at rated speed.
  • Temperature rise and commutation qualities can be observed.

 

Retardation or running down test:

  • Applicable to shunt motors and generators.
  • Used for finding the stray losses.
  • Machine is speeded up slightly beyond its rated speed and then supply is cut off from the armature while keeping the field excited.
  • Armature will slow down and its kinetic energy is needed to meet rotational losses. i.e., friction and windage losses.

 

Swinburne’s Test:

  • This test is performed no load.
  • The rated speed is adjusted by the shunt field resistance.
  • As it is a no load test, it cannot be done on a dc series motor.
  • Give efficiency of DC machine.

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