CT Secondary

Usman,

U cant leave secondary of CT open circuit as if it is kept open on load their will be no current in the secondary winding & as a result their will be no back e.m.f to counter the voltage which is being build up due to load in primary winding as a result high voltage will develop in the secondary winding which will be not only hazardous to the working personnel but can also lead to insulation failure leading to damage of CT.

can we not leave secondary of c.t open?

NO AS THIS IS VERY DANGEROUS!

This is a common question asked on CR4. Please use the search function on the right hand side of the screen to look at previous threads on the subject.

Dear Sir,

This forum expects some decency in writing. Kindly avoid "short cuts like y

Etc". This will improve your image & maturity. Excuse me for my frank comments.

(1) CT seconary is closed so thar the current can be measured.

(2) Open CT secondary will induce high Open end voltahe as indicated by our

esteemed readers.

(3) One end of the The secondary is earthed invariablly - cam some one explain

the reasons.

Manroop.Chennai.

The fundemetals are simple for any transformers. We require basic transformer equation and Ohms law to explain this.

For any primary ampere turns there should a secondary matching ampere turn

I1 N1 = I2 N2 ( Transformer equation )

If you leave your secondary of CT open circuited, there is no secondary ampere turn

ie I2 =0 , and the poor current transformer does not have enough muscle to oppose primary ampere turn and the current which passes through bus bars.

Now transformer has to some how try to establish secondary ampere turn to respect laws of physics.

Only way to establish secondary ampere turn is by increasing secondary voltage to over come the high value of Resistance ( air - since secondary is open cktd )----- OHMS LAW

The CT output voltage becomes so high some times that it breaks through transformer secondary insulation resistance and the CT explodes !!!!!

Well said & thanks.

Manroop.Chennai

Check out IEEE standard C57.13.3

Grounding of CT terminal ( at only one point ) is essential for Safety and correct operation of protective relays. To assure safe and reliable operation, the neutral of the CT secondary should be grounded at one location.

Otherwise if ungrounded, the secondary system may behave as ungrounded system with all its ill effects.