Q.What is the need of doing polarity test?
A.Polarity is very sensitive in case of differential and restricted earth fault protections,so it is necessary to identify the polarity of CT.
PROCEDURE:
remove all external connections before doing test.
remove all external connections before doing test.
1.Connect analog galvanometer to secondary core winding(+ve to S1 and -ve to S2).
2.Apply dc voltage in impulse fashion ( apply and remove) to primary conductor (+ve to P1 and -ve to P2).
3.Observe the deflection in meter.
4.If the deflection is in clock wise then its polarity is correct.other wise polarity is wrong.
Q. Why we are using galvanometer not ammeter?
A. Galvanometer only senses small currents (as we are applying 1.5 volts to primary,secondary current is low).
Q. Why we apply dc voltage is in impulse fashion,not continiously?
A. For pure dc we cannot generate time varying flux,if not transformer action will not developed.
Q.What will happen ac voltage?
A. pointer in galavonameter will continiously oscilates which we cannot idetify the polarity.
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