To Perform Field Test on DC Series Motor


  • The brake test is applicable only for small DC series motor. 
  • The field test is carried out on large DC series motor in order to find out various losses and efficiency.
  • There are two similar DC series motor requires in this test. 
  • The field winding of both series motors are connected in series in order to make iron losses of both machines are equal. 

To Perform Hopkinson Test on DC Shunt Machines


  • This test is also known as back to back test. This test is carried out for two identical shunt machines. 
  • The two machines are mechanically coupled and so adjusted that one machine act as a motor and the other machine acts as a generator. 

How to separate out the Eddy current loss and Hysteresis loss in the DC Machines?

There are mainly two types of losses in the DC Machines

( 1 ) Variable losses : Armature copper loss and Field copper loss

( 2 ) Constant losses : Iron losses and Friction and winding losses

  • We can find out constant losses and variable losses separately with the help of both Field test and Hopkinson test. We can separate out following test.


How the hysteresis loss and eddy current loss of the transformer can be separated?


  • There are no moving parts in the transformer therefore the mechanical losses are zero. 
  • The open circuit test and short circuit test on transformer is performed in order to find out core losses and copper losses.  
  • We will study how to separate hysteresis loss and eddy current loss.


Working of Induction Regulator


  • When the load on the supply system is changed, the voltage at the consumers’ terminal also is changed. 
  • The voltage control is necessary in order to keep the voltage variation within certain limits for reliable service to the consumers. 
  • The study of single phase induction regulator is explained here.

Methods of Improving String Efficiency

There are following methods used to improve string efficiency of suspension insulators

( 1 ) Using long cross arm

  • The unequal voltage distribution across the string is done by charging current passes through shunt capacitance ( Capacitance between insulator metal pin and tower ).
  • Charging current I = V / XC   =  VωC

String efficiency of Three Suspension insulators


String of Suspension Insulator Disc

  • Figure shows three suspension insulators. Each suspension insulator has two metallic links therefore it has its own capacitance and it is called as mutual capacitance or self capacitance.