What happens if a current transformer secondary connection is opened-circuited while the primary is active?

When a current transformer (CT) secondary connection is open-circuited while there is current flowing in the primary, it can lead to potentially dangerous conditions. In normal operation, the secondary of a current transformer is designed to operate with a closed circuit, allowing the proportional current to be stepped down safely.

If the secondary is allowed to open-circuit, the transformer continues to generate a high voltage across the secondary terminals due to the magnetic flux created by the primary current. This high voltage can exceed the insulation rating of the transformer, leading to insulation breakdown. Moreover, this condition poses significant safety hazards, as it can result in electric shock or equipment damage. Furthermore, there is a risk of causing arcing or sparking at the open terminal points, which can lead to further hazards.

Thus, the situation highlights the importance of ensuring that current transformer secondaries are never left open-circuited during normal operation to maintain safe and effective functioning.