Explain the procedure for finding out the polarity and ratio test in a CT with circuit diagram.

Explain the procedure for finding out the polarity and ratio test in a CT with circuit diagram. 
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Polarity test: Connect the circuit as shown in figure with a battery, switch and AVOmeter. Now momentarily close the switch S and see the deflection in the AVOmeter. If it is in the direction as shown in the figure, then the polarity of the CT is correct. If it is in opposite direction the polarity of CT is not correct. Polarity test is very important because if polarity is not correct in differential protection the relay will fail to act when fault occurs. 

Ratio test: Connect circuit as shown in figure (2). Slowly increase the current. Take down the readings of A1 and A2. Then see whether it confirms to reading of nameplate. Ratio = A1/A2. 


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