Friday, 6 April 2018

Which Is The Indirect Methods For Testing Of Transformer???

You Know Which Indirect Test Use For The Testing Of Transformer?? 



There Is The Indirect Method For Testing Of The Electrical Transformer!!  And How We Can Proceed The Indirect Methods On The Electrical Transformers!!! 




The Performance of a Transformer at any load and Power Factor can be determined without actually loading the transformer by conducting the following tests:




  1. (i) Open Circuit (O C.) test and
  2. (ii) Short Circuit (S. C.) test

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These tests are convenient and economical because the power required to test a transformer is very small.


(i) Open circuit or No load test 



The Aim Of Conducting this test is to determine the following.
[ Here This Losses Accure In Electrical Machines ]
  • (a) Iron losses
  • (b) No-load current and
  • (c) No-load equivalent circuit parameters (Ro and Xo)


The Experimental Circuit diagram for conducing open circuit (o.c.) test on a transformer is shown in figer(A)

In this test, The Primary Winding (preferebly low voltage winding) is supplied primary and frequency rating of the with normal voltage as per the transformer and the secondary (High Voltage Winding) is left open


  • To measure no-load current and no load power input, an Ammeter And Wattmeter of low range are connected in the primary circuit. The Supply Voltage can be measured with the help of voltmeter



  • As the iron losses depend upon supply Voltage And Frequency, this test is performed at normal supply voltage and frequency


Since the Normal Voltage is applied to the primary winding, the flux set up in the core of transformer will have a normal value so that normal iron losses will occur


The no-load primary current being very small (2 to 5% of full current), the copper losses in the primary winding will be negligible and there will be no Copper Losses in the secondary winding, sin open circuited us the reading of the wattmeter indicates practically the iron losses under No-load condition .


It is preferred to keep h.v. winding open and normal voltage applied during this test because it is difficult to obtain high voltages in the laboratories.


Also in certain cases, no load current of h.v. winding maybe extremely small, which might not be measured accurately.


(ii) Short Circuit Test

The purpose of this test is to determine the following:


  1. (a) Full-load copper losses
  2. (b) Equivalent impedance (Z1, or Z2) referred to metering side.
  3. (c) Voltage regulation



The Experimental Circuit diagram for conducting short circuit test on a Single Phase Transformer is shown in figer(B).


In this test, usually low voltage winding is kept short-circuited and a reduced voltage of Normal Frequency (hardly 5 to 8% of rated voltage) is applied to the high voltage winding.

The applied reduced voltage is gradually increased till full-load currents are flowing both in primary and secondary windings


As The Applied Voltage is very low, the iron losses will be very small and can be neglected.


Hence the total losses occurring under this test are mainly the copper losses of both the windings, which are indicated the wattmeter.

Question part of this Article  :



(1)when The performance of a transformer at any load and power factor can be determined without actually loading the transformer by which test???
Ans:(i) Open Circuit (O C.) test and
 (ii) Short Circuit (S. C.) test


(2)O.C. and S. C. testes which type of test and why??? 
Ans:These tests are convenient and economical because the power required to test a transformer is very small.


(3)by open circuit test which type property we can find?? 
Ans:The aim of conducting this test is to determine the following.
(a) Iron losses
 (b) No-load current and
(c) No-load equivalent circuit parameters (Ro and Xo)



(4)In open circuit test which winding will be open?? 
Ans:H.V.


(5)using short circuit test which property we can find?? 
Ans: (a) Full-load copper losses
(b) Equivalent impedance (Z1, or Z2) referred to metering side.
(c) Voltage regulation


(6)In short circuit test which winding will be shorted??? 
Ans:L.V.


(7)When in the short circuit test the applied voltage is very low that timr the iron losses will be ???
Ans:very small


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