A. Open circuited
B. Short circuited
C. Any of these
B. Short circuited
C. Any of these
D. None of above
Answer: A. Open circuited
Answer: A. Open circuited
Explanation:
Why current transformer secondary should not be opened.
- If the secondary winding is open-circuited with energized primary, the primary MMF remains the same while the opposing secondary winding MMF reduces to zero.
- In this condition, the resultant MMF becomes very large. This large MMF produces a large flux in the core till it saturates.
- This large flux links with secondary winding and induces a high voltage in the secondary winding. This could be dangerous to the transformer insulation and to the person who has opened the circuit.
- Also, the eddy current and hysteresis losses would be very high under these conditions and due to this the CT may be overheated and damaged.
- Even it does not occur, the core may become magnetized permanently and this gives considerable ratio and phase angle errors.
- Mostly, CTs are provided with a switch or short-circuiting link at the secondary winding terminals. If such a link is available, it should always be short-circuited before any change is made in the secondary winding circuit with primary winding energized.
- When a CT is used for measurement, its secondary winding can be short-circuited safely since it is practically short-circuited the impedance of the burden (i.e. an ammeter, CC of wattmeter etc.) is very small.