A. Greater than one
B. Lesser than one
C. Equal to one
D. None of the above
Answer: B. Lesser than one
Explanation:
- Current transformers have turns ratios less than one.
- The most important precaution in the use of a CT is that in no case should it be open-circuited (even accidentally).
- As the primary current is independent of the secondary current, all of it acts as a magnetizing current when the secondary is opened.
- This results in deep saturation of the core which cannot be returned to the normal state and so the CT is no longer usable.
- Again, due to large flux in the core, the flux linkage of secondary winding will be large which in turn will produce a large voltage across the secondary terminals of the CT.
- This large voltage across the secondary terminals will be very dangerous and will lead to insulation failure and there is a good chance that the person who is opening the CT secondary while primary is energized will get a fatal shock.
- If, for any reason, the instrument connected to the secondary of CT is to be removed, then the secondary of CT must be short-circuited by a fairly thick wire.
- These instrument transformers are also used in the power system in conjunction with protective relays.
- For safety purposes, the secondaries of these transformers are grounded.