The difference between residual current and zero sequence current of precision transformer
Dec 04, 2023| Zero sequence current and residual current are different. The zero sequence current measures Ia+Ib+Ic. When the load is symmetrical, it is equal to 0; but in reality, it cannot be equal to 0, and there will always be an unbalanced current. The residual current is measured as Ia + Ib + Ic + N. At this time, regardless of the load, it is normally equal to 0.
Therefore, the residual current will be more sensitive than the zero-sequence current. The working principle of the low-voltage leakage zero-sequence current transformer. If a current transformer is connected to a three-phase four-wire, the induced current corresponding to the precision transformer will be zero at this time. When an electric shock occurs or a leakage fault occurs in the circuit, a leakage current flows through the circuit. At this time, the phasor sum of the three-phase currents passing through the transformer is not equal to zero. The phasor sum is: Ia+Ib+Ic=I (Leakage current) In this way, there is an induced voltage in the secondary coil of the transformer. This voltage is added to the electronic amplifier circuit of the detection part and compared with the predetermined operating current value of the protection zone device. If it is greater than the operating current, even if the sensitive relay operates, the effect The actuator is tripped.
The precision transformer connected here is called a zero-sequence current transformer. The phasor sum of the three-phase currents is not equal to zero, and the current generated is the zero-sequence current.