Which of the following statements are true for synchronous motor losses?

A) Friction and windage losses increase with the cube of speed.

B) The Eddy current loss is reduced by laminating the core.

C) Copper losses are independent of load.

D) Core losses increase with the square of the load.

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  1. B and C
  2. A and B
  3. A and D
  4. C and D

Answer (Detailed Solution Below)

Option 2 : A and B
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Detailed Solution

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Power flow in the synchronous motor
 

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Different types of losses:

1.) Copper losses

  • The various windings of the synchronous machine such as armature and field winding are made of copper and have some resistance. When current flows through them, there will be power loss proportional to the square of their respective currents. These power losses are called copper losses.
  • Copper losses depend on the load because they are proportional to the square of the current, which increases with load.
     

2.) Core losses

  • The losses that occur in the iron parts of the motor are called core losses or magnetic losses.
  • Core losses are generally constant and depend on voltage and frequency rather than load. They do not typically increase with the square of the load.
  • These losses consist of the following: Hysteresis loss: To minimize this loss, the armature core is made of silicon steel which has a low hysteresis constant.
  • Eddy's current loss: To minimize this loss, the armature core is laminated into sheets(0.3-0.5mm).
     

3.) Mechanical losses

  • As the field system of a synchronous machine is a rotating part, some power is required to overcome Friction and windage losses.
  • The mechanical loss which is the summation of the friction and windage losses is related to the cube of the operating speed.
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