Friday, 9 February 2018

Different Types Of Losses In The DC Machine And Their Effect On The Machine! !

Different Types Of Losses In The DC Machine And Their Effect On The Machine! !



Description About The All Different Types Of Losses Which Occur In DC Machine And Their Details .





The Losses Occurring In DC Machines can be listed as below:
(1) copper losses
(2) Magnetic or iron losses
(3) Mechanical losses
(4) Stray load losses


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(i) Copper losses

These losses occur in those parts of de machines which carry electric current Copper losses occur due to the current flowing in Various Windings of the machine.

These losses are directly proportional to the square of current nowing in the winding and the ohmic resistance the winding .

The various copper losses occurring in the windings are





  • (A)  Armature copper loss
  • (B) Shunt field copper loss
  • (C) Series field copper loss
  •  (D) Copper loss in interpole winding
  • (E) Brush contact loss


Shunt field copper loss is constant for shunt and compound wound dc machines. All other copper losses (Armature circuit losses) are called variable losses because these are directly proportional  to the square of armature current which varies with the load.

The Armature Copper Loss is about 30-40% of totle full load losses amd field copper losses are about 20-30%of full load losses.




(ii)  Magnetic losses

These losses are also called iron loss or core loss.
These losses occur in Armature Core And Teeth where the iflux is changing.
Iron losse consists of (1) Hysterisis losses and (2) Eddy current losse.

Since field is constant and dc machines are usually operated at constant speed, these losse are almost constant. These are about 20% to 30%of full load losses.

(a)  Hysterisis losses



This loss is due to reversal of Magnetism Of The Armature Core.
These losses pccur in armature core teeth of the dc machine.
Hysteresis Losses can be reduced by using core material of silicon steel which has low hysterisis coefficient.

(b) Eddy current loss

When Armature Core Rotates in magnetic field of poles it also cuts the magnetic flux. Hence an emf is induce in the body of the core according to the low of electromagnetic induction. This emf set up current in the body of the armature core and its know as eddy current.
To Minimize Eddy Current losses the armature core is made of thin laminated stamping. The thickness of laminating used for armature core is 0.35 to 0.5 mm.

(iii) Mechanical losse

Due to friction of bearing air friction or windage losses in dc machins. These are known as Mechanical Losses.

  • (a)  Bearing and brush friction losses
  • (b)  Winding loss or air friction of rotating armature.

These losses are about 10-20% of totle full load losses.

(iv)  stray losses

There are certain type of losses which can not be easily determined  .
They appear when machine is loaded. These inderminanble losses are called Stray Losses and are due to the following reasons. 

  • (1)Distortion of flux because of armature reaction
  • (2)due to eddy current in conductore
  • (3)short circuit current in the armature coil undergoing commutation.

Stray Losses may be assumed 0.5-1%of the power output for machine.

Questions Related To This Topic:

1)list The losses occurring in dc machines ???
Ans: listed as below:
(1) copper losses
(2) Magnetic or iron losses
(3) Mechanical losses
(4) Stray load losses

2) give The various copper losses occurring in the windings ??????
Ans:
(A)  Armature copper loss
(B) Shunt field copper loss
(C) Series field copper loss
 (D) Copper loss in interpole winding
 (E) Brush contact loss

3)The armature copper loss is about ______% of totle full load losses amd field copper losses are about ______%of full load losses.???
Ans:30-40 and  20-30

4)Magnetic losses is also known as???? 
Ans:These losses are also called iron loss or core loss.

5)magnetic loss consist which losses???
Ans:Iron losse consists of (1) Hysterisis losses and (2) Eddy current losse.

6)magnetic loss  are about _____of full load losses.???
Ans: 20% to 30%

7)explain hysteresis losses in dc machine??? 
Ans:Hysterisis losses

This loss is due to reversal of magnetism of the armature core.
These losses pccur in armature core teeth of the dc machine.
Hysteresis losses can be reduced by using core material of silicon steel which has low hysterisis coefficient.

8)define eddy current??? 
Ans:When armature core rotates in magnetic field of poles it also cuts the magnetic flux. Hence an emf is induce in the body of the core according to the low of electromagnetic induction. This emf set up current in the body of the armature core and its know as eddy current

9)mechanical losses consists which losses??? 
Ans:(a)  Bearing and brush friction losses
(b)  Winding loss or air friction of rotating armature.
These losses are about 10-20% of totle full load losses.

10)stray losses occurring because of??? 
Ans:(1)Distortion of flux because of armature reaction
(2)due to eddy current in conductore
(3)short circuit current in the armature coil undergoing commutation.


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