DC Immune current transformer theory

Electrical Specification

(Customized is available)

Rated Primary Current	100A
Max Primary Current	150A
Rated Secondary Current	10mA
Accuracy	0.1~2.0
Electrical Strength	3000VAC 1mA60s
Load Resistance	40Ω
Rated Frequency	50/60HZ

Current transformers are key equipment for power production and household metering and protection. Due to the application of a large number of rectification, frequency conversion and switching power supply equipment, the DC component in the circuit can not be ignored.
Under rated conditions, the voltage transformer runs near the inflection point. The purpose of this is to ensure the application of the maximum efficiency of the voltage transformer, and this part of the DC current will generate a certain amount of DC magnetic field in the voltage transformer.

This DC The superposition of the magnetic field and the AC magnetic field that established the magnetic field in the original voltage transformer will cause the working point of the voltage transformer to move up, and the working point moves up beyond the inflection point. The voltage transformer is working in a saturated state. In severe cases, the voltage transformer works In a serious saturation state, it will cause primary side excitation current distortion, increased high-order harmonic components, insulation aging, severe vibration, noise fixtures, high saturation of the iron core, local overheating, etc. The system voltage fluctuates and loses a lot of load.
Therefore, in order to make the transformer work normally even with a large DC component, it must be ensured that the transformer core is not saturated when the AC and DC superimpose magnetization.