8 March 2020

DC Motor Interview Question Answer - 3


41
Why the swinburne test is not performed on the DC series motor?


Swinburne Test
  • The DC series motor never starts on no load. As the Swinburne test is no load test therefore it is not performed on DC series motor.


42
Describe the advantages and disadvantages of swinburne test.


Advantages
  • As it is a not load test, input power required for higher rating machine is small. The efficiency can find out at any load condition.

Disadvantages
  • As it is no load test, the effect of armature reaction and iron losses are not considered from no load to full load condition.
  • The commutation condition and temperature rise do not know at full load condition. 
  • The effect of rise in the temperature on shunt field resistance is not considered.


43
Why Hopkinson test is also called as regenerative test?        


Hopkinson test as regenerative test
  • The two shunt machines in the Hopkinson test are connected in parallel and output of the first machine ( Motor ) is given to the input of the second machine ( Generator ). 
  • The output of the second machine feedback to input to the first machine. Therefore it is also called as regenerative test.


44
How field current is deciding factor in the Hopkinson test for machine runs as a motor or generator?


Stronger field
  • Generator

Weaker field
  • Motor


45
There are two same rating shunt machines required in the Hopkinson test. Whether the efficiency of both machines are same or different? Why?


Hopkinson Test
  • The two shunt machines in the Hopkinson Test are used and the efficiency of the both machines are not same because of armature current and shunt field current are not same in both machines.


46
Why field test is not called as regenerative test?


Field test
  • The field test is applicable only for pair of series machines. 
  • The output of the first machine in this test is given to the input of the second machine and output of the second machine is dissipated in the load resistance.  
  • The output of the second machine is not feed back to the input of the input machine therefore field test is not called as regenerative test.


47
Why the iron losses and mechanical losses are same for pair of series machines in the field test?


Field test
  • The field winding of pair of the series machines in the field test is connected in series and both machines are run at same speed therefore the iron losses and mechanical losses are same in the field test.




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