The difference between zero sequence current transformer and current transformer

- May 11, 2020-

The function of current transformer is to convert primary current with large value to secondary current with small value through a certain transformation ratio, which is used for protection and measurement. For example, a current transformer with a transformation ratio of 400/5 can convert the actual 400A current to 5A current.

Principle: The basic principle of zero-sequence current protection is based on Kirchhoff ’s current law: the algebraic sum of the complex current flowing into any node in the circuit is equal to zero. When the line and electrical equipment are normal, the vector sum of each phase current is equal to zero. Therefore, the secondary winding of the zero sequence current transformer has no signal output, and the actuator does not operate. When the ground fault occurs, the vector sum of each phase current is not zero. The fault current causes magnetic flux in the ring core of the zero sequence current transformer, and the induced voltage on the secondary side of the zero sequence current transformer causes the actuator to move Trip device to switch the power supply network to achieve the purpose of ground fault protection.

Zero-sequence transformer function: When electric shock or leakage fault occurs in the circuit, the protection action and cut off the power supply.

Use: You can install a current transformer on each of the three-phase lines, or let the three-phase conductors pass through a zero-sequence current transformer together, or you can install a zero-sequence current transformer on the neutral line N and use it to detect Vector sum of three-phase current.