Why should the secondary circuit of a current transformer be kept closed?

Why should the secondary circuit of a current transformer be kept closed?

The current transformers are always used with the secondary windings circuit closed through ammeters, current coils of watt-meters or relay coils. Its secondary winding circuit should not be opened while its primary winding is energized. A violation of this precaution may lead to serious consequences.

Why CT’s terminals are not kept open?

As CT is oil filled, because of overheating, the oil of CT will get boil and start to vaporize. Because of vaporization of CT oil, the CT housing will get pressurized and blast. This blasting will lead to fire and smoke.

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Why CT secondary should be shorted?

Unless a burden (i.e. meters, relays, etc.) is connected to the CT, current transformers should always be shorted across the secondary terminals. The reason is very high voltages will be induced at the terminals.

Why is PT secondary shorted?

Q6) why secondary of pt. should not be short circuit? Answer: A VT is a “step-down transformer” that steps down voltage from a very high voltage level (200KV,) to a lower level (110V). Short circuiting the secondary would burn out the windings.

Is it safe to open the secondary winding of a transformer?

Hence never open the secondary winding circuit of a current transformer while its primary winding is energized. Thus most of the current transformers have a short circuit link or a switch at secondary terminals. When the primary is to be energized, the short circuit link must be closed so that there is no danger of open circuit secondary.

Why is a voltage transformer used in virtual open circuit?

The voltage transformer is a transformer that is connected to a very large impedance (use in virtual open circuit mode). A voltage transformer is designed to give the secondary a voltage which is proportional to that applied to its primary. For a voltage transformer (VT) the ratio of voltage between the primary and the secondary is constant.

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What happens if current transformer ( CT ) seconday is left open?

If it is left open, then current through secondary becomes zero hence the ampere turns produced by secondary which generally oppose primary ampere turns becomes zero. As there is no counter m.m.f., unopposed primary m.m.f. (ampere turns) produce high flux in the core. This produce excessive core losses, heating the core beyond limits.

Why is the voltage of a voltage transformer constant?

A voltage transformer is designed to give the secondary a voltage which is proportional to that applied to its primary. For a voltage transformer (VT) the ratio of voltage between the primary and the secondary is constant. The secondary voltage is independent of the load. If Z is the load impedance of a VT, then at the secondary, we have: