WINDING RESISTANCE TEST....

Q. What is the need of doing winding resistance test?
A.  In order to identify any short circuit between winding turns,estimate the copper loss of machine as it will heat up the machine.

Q. We are using separate kit for finding resistance instead of using multi meter,why?
A. By using multi meter we cannot get prescribed value in micro ohms and we know that winding resistance value is vary low so multi meter probe wires resistance also added into winding resistsnce of transformer.

   by using multi meter we are applying voltage and so that current is flowing,so we are finding resistance.

     But by using TRM (transformer winding resistance) kit we are injecting DC current and measuring voltage drop across only winding (in this case probes will not included) voltage.so by dividing voltage with current internally we will get DC winding resistance,in order to get AC resistance we should multiply with factor 1.6 (because of skin effect) .

           

             voltage leads should be inside current leads should be out side.....

Q. what will happen if those leads are inter changed?

A. Value we get is not exactly correct,because for low resistance measurement ammeter-voltmeter method is suitable (having low loss in meter).For measuring high resistance voltmeter-ammeter method is suitable. As we are measuring low values it is advisable to connect voltage leads inside the current leads.

Q. Why we should do this test at last?

A.  We are injecting 10 - 100 milli amps,so the core will be in magnetization mode after doing the test for some time,so remaining test results will not be accurate.

PROCEDURE:

1.Remove all external connection before conducting test.

2.Connect the all wires of kit as per above diagram and connect the grounding wires also.

3.Inject the 10 milli amps with kit.

4.Apply for one minute.

5.Note down the resistance value shown by kit.

6.Discharge the charge in winding through kit or to ground by using external earthing rod.

what we got the value is DC resistance,multiply with factor 1.6 to get AC resistance....