What happens when you open circuit a current transformer

FAQ | Mar 04,2023

When an open circuit is created in the secondary winding of a current transformer, it effectively disconnects the load from the transformer. This condition is sometimes referred to as an “open secondary” or “secondary open”.

In this situation, no current flows through the secondary winding of the transformer, which means that there is no load for the transformer to supply. As a result, the primary winding of the transformer experiences a high impedance, which can cause a phenomenon called “voltage build-up”. This happens because the transformer core can become magnetically saturated due to the absence of a secondary load, which causes the primary voltage to increase.

If the voltage build-up becomes excessive, it can lead to insulation failure and damage to the transformer. Therefore, it is important to avoid creating an open circuit in the secondary winding of a current transformer while the primary winding is energized.

In practical applications, protective devices such as fuses or circuit breakers are typically installed in the secondary circuit of current transformers to prevent an open circuit from occurring. These devices interrupt the current flow in the event of an overload or fault, which helps to protect the transformer from damage.

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