Why current transformer secondary is always short circuited

FAQ | Mar 16,2023

Current transformers (CTs) are designed to measure high currents in electrical systems and provide a proportional low-level current output that is safe and easy to measure. The CT’s secondary winding is short-circuited because this configuration allows the CT to operate safely and accurately.

When the CT’s primary winding is connected to a high-current conductor, it induces a current in the secondary winding proportional to the primary current. The secondary winding is designed to have a very low resistance, typically just a few ohms, so that the output current remains proportional to the primary current.

If the secondary winding of the CT were left open-circuited (i.e., not connected to a load), the induced current would continue to flow through the winding, leading to high voltages that could potentially damage the CT or any connected measuring equipment. On the other hand, if the secondary winding were connected to a high impedance load, the CT’s output voltage would be too high, leading to measurement errors and potentially damaging the load.

By short-circuiting the secondary winding, a low-resistance path is provided for the induced current to flow, allowing the CT to operate safely and accurately. The short-circuit also ensures that the CT’s output current is limited to a safe level, typically a few amps, which is easy to measure and does not pose a risk of damage to the connected measuring equipment.

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