A current transformer must never be operated with secondary winding open-circuited. It is because:a)A very high flux is produced in the core.b)The magnetising current is reduced.c)A very high voltage is induced in the primary.d)The primary terminals are short-circuited.Correct answer is option 'A'. Can you explain this answer?

Question

Answer

Introduction:
A current transformer is a type of transformer that is used to measure electric current. It is designed to step down the current to a level that can be safely measured by instruments or meters. However, it is important to never operate a current transformer with the secondary winding open-circuited. This is because it can lead to several undesirable consequences.

Explanation:
A. Very high flux is produced in the core:
When a current transformer is operated with the secondary winding open-circuited, the current flowing through the primary winding is not balanced by an equal and opposite current in the secondary winding. This results in an excessive amount of current flowing through the primary winding, which leads to a very high flux being produced in the core of the transformer.

B. Saturation of the core:
The high flux in the core can cause the magnetic core material to saturate. Saturation occurs when the magnetic material reaches its maximum magnetic flux density. When the core saturates, it can no longer effectively transfer the magnetic energy from the primary winding to the secondary winding. This leads to inaccurate measurements and can damage the transformer.

C. Excessive heating:
The high flux in the core also causes increased core losses, leading to excessive heating. This can result in damage to the insulation materials and may even lead to a breakdown of the transformer.

D. Increased voltage stress:
When the secondary winding is open-circuited, there is no load on the transformer. As a result, the primary voltage is not properly regulated, leading to a very high voltage being induced in the primary winding. This can cause insulation breakdown and damage to the transformer.

Conclusion:
Operating a current transformer with the secondary winding open-circuited can lead to several detrimental effects, including high flux in the core, saturation of the core, excessive heating, and increased voltage stress. These consequences can result in inaccurate measurements, damage to the transformer, and potential hazards. Therefore, it is crucial to never operate a current transformer with the secondary winding open-circuited.

Answer

A current transformer must never be operated with secondary winding open-circuited. If the secondary is open, the whole of the primary current becomes the magnetising current. This gives rise to a very high flu in the core, inducing a very high voltage in the secondary. This high voltage will damage the insulations, making it dangerous for the operator.

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