Polarity Check
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POLARITY CHECK:
Polarity check is necessary to see the relative polarity of the primary and secondary
terminals when terminals are not marked or to establish the correctness of the marking if already
marked. In otherwords the polarity checking consists actually in making sure that the
designations P1 and P2 made on the leads of the primary winding and S1 and S2 made on the
leads of the secondary winding corresponds to the winding start and Finish ends.
CHAPTER-II
The d. c. source, a dry cell or storage battery of 4-6 V is connected in series with the
primary winding of the CT through switch. The positive pole of the battery is connected to the
beginning of the primary winding and the negative pole to the end of the primary.
While closing and then opening switch, watch the indicating instrument connected across
the secondary winding to see in which direction its pointer deflects. If, when the primary circuit
is closed, the pointer deflects to the right and then deflects to the left when the circuit is broken.
It is a sign of like polarity (and correct marking) of the CT primary and secondary terminals, one
of the which connected to the positive pole of the battery, the other to the positive terminal of the
indicating instrument.
2. CHECKING CURRENT RATIO:
The ratio of the CT is checked by dividing the value of the primary current I1, by that of
the secondary current I2 and comparing it with the rated value.