MAGNETIC BALANCE TEST....

Q. What is magnetic balance?What is the need?

A.  It was not in case of single phase transformers.magnetic balance test was in case of only poly winding transformers. 

     We can connect three phase transformers in two fashions,

         1. delta 

         2. star

DELTA FASHION:

     In case,failure of one phase in transformer (either R,Y,B) then only one limb of transformer will produce flux and in remaining two limbs will provide return path for that flux, THE MAIN AIM OF THIS TEST IS TO PROVE,FLUX PRODUCED BY ONE LIMB IS THE SUM OF FLUXES OF OTHER TWO LIMBS SO THAT WE CAN SAY CORE DON'T HAVE ANY PROBLEM FOR PATH OF FLUX.The flux passing in two limbs will induce voltage on winding placed on those respective limbs. so by logically,the sum of voltages induced on remaining limbs must be equal to voltage applied to one of the limb.

                                         

STAR FASHION:

     In case,failure of two phase in transformer (either R,Yor Y,B or B,R) then only one limb of transformer will produce flux by using neutral point, THE MAIN AIM OF THIS TEST IS TO PROVE,FLUX PRODUCED BY ONE LIMB IS THE SUM OF FLUXES OF OTHER TWO LIMBS SO THAT WE CAN SAY CORE DON'T HAVE ANY PROBLEM FOR PATH OF FLUX.The flux passing in two limbs will induce voltage on winding placed on those respective limbs. so by logically,the sum of voltages induced on remaining limbs must be equal to voltage applied to one of the limb.

                                         

SIMILARLY, 

                   2)    ∅ B=∅ A  +  ∅ C

                        100%=50%   +   50%

     

                   3)         ∅ C=     ∅ B      + ∅ A     

                    100%       = 60 - 80 % +  40 - 20 %

Q.Why it is not exactly 50 - 50 in case of 1&3?

A. In case 2, we have almost equal reluctance path for left side and right side (limb A & C).but in case 1&3 we have high and low reluctance paths for fluxes for middle and outer limbs.So value may vary from 60-80% of value.

  PROCEDURE:

                  Apply three phase 415v voltage to primary winding of transformer and remove any one phase for delta fashion winding and remove any two winding for star fashion winding.note down the voltages in three phases by using multi meter in primary winding and secondary   winding.

                         line to line voltage in case of delta fashion.

                         line to neutral voltage in case of star fashion.

              Repeat the same procedure for remaining two cases.

NOTE: While doing this test remove neutral earthing of transformer and remove all external connections.