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.
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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.