Below we have a current transformer used to measure a high AC current:
Current transformers are used to reduce the line current to a level acceptable for measurements, control, and protection.
When a current transformer is connected to a live system on the primary-side, its secondary behaves as a current source.
- Therefore, the secondary terminals of CT cannot be open circuited; otherwise, the resulting high voltages may damage the CT.
- A shorting switch is normally provided so that the secondary terminals of the CT are short circuited once the device connected to its terminals is removed.