Composition and working characteristics of current transformer

1. The number of primary turns is small, and the number of secondary turns is large

For current transformers used in power systems, the primary winding is usually the incoming and outgoing wires of primary equipment, with only 1 or 2 turns; there are many secondary turns.

2. The working magnetic density in the iron core is very low, and the magnetic density is large when the system fails

During normal operation, the working flux density in the iron core of the current transformer is very low, and the ampere-turn balance is maintained between the primary and secondary. When the system fails, due to the large fault current and high secondary voltage, the excitation current increases, the magnetic density in the iron core rises sharply, and even saturates the iron core.

3. High internal resistance, current source

Under normal working conditions, the magnetic density in the iron core is very low, the excitation impedance is large, and the number of secondary turns is large. Seen from the secondary side, its impedance is very large. Compared with the internal resistance of the current transformer, the load impedance is negligible, so the change of the load impedance has little effect on the secondary current, so it can be called a current source.

4. Small secondary load is required

If the secondary load of the current transformer is large, its secondary voltage is very high during operation, and the excitation current will inevitably increase, thereby increasing the error of current transformation.

5. The secondary circuit shall not be open

If the secondary circuit is open during operation, the secondary current disappears, and the demagnetization effect also disappears, and the magnetic density in the iron core is very high; and because of the large number of secondary turns, the secondary voltage will be very high, sometimes up to Thousands of volts, endangering secondary equipment and personal safety.