The working principle of current transformers (CT) during a short circuit.

Working Principle

In normal working conditions, the secondary circuit of a current transformer (CT) is closed and has very low impedance, causing the CT to operate in a near-short-circuit state. When a short circuit occurs, the behavior and characteristics of the current transformer change significantly.

Performance during a short circuit

1. Voltage Increase: In a short-circuit scenario, due to the extremely low impedance of the secondary circuit, the secondary current theoretically tends to infinity. However, in reality, limitations of materials and the presence of protective mechanisms prevent this infinite increase. Instead, an abnormally high voltage appears on the secondary side, a phenomenon known as open-circuit overvoltage.

2. Protective Mechanism Trigger: To prevent such high voltage from damaging equipment and personnel, modern current transformers are often equipped with overvoltage protectors (CTBs). These protectors can quickly respond when abnormal high voltage is detected, protecting the secondary side equipment through voltage limiting and short-circuiting.

3. Indication and Alarm: Some advanced protective devices display the specific location of faults on the panel and provide passive signal output, allowing operators to quickly identify and handle problems.

The impact of a short circuit

• Equipment Damage: Without taking appropriate protective measures, a short circuit can cause damage to current transformers and the connected measuring instruments, relay protection equipment, etc.

• Safety Hazard: The high voltage and large current generated by a short circuit may cause fires or other safety incidents, posing serious threats to operators.

• System instability: Short circuits can also affect the stability of the entire electrical system, leading to relay operation failure and subsequently impacting the overall protection function of the system.

Conclusion

In summary, current transformers exhibit the characteristic of voltage rise under short-circuit conditions and may trigger built-in protective mechanisms to prevent further damage. To ensure the safety and stable operation of the system, appropriate preventive measures and protection strategies must be taken to address short-circuit conditions in current transformers.