Difference Between Residual Current Transformer and Zero Sequence Transformer

Residual current transformer:Residual current transformer is the detection element of leakage protector. Its main function is to detect the residual current (grounding fault current such as electric shock and leakage) of the main circuit passing through the transformer core, and convert the residual current of the primary circuit into the output voltage of the secondary circuit. Residual current transformer is one of the most critical components of leakage protector.

The excitation current of the primary circuit of residual current transformer is very small and works under the condition of weak magnetic field. For the residual current protection appliance with rated residual action current of 0.006a, the minimum working magnetic field strength is only about 0.080a/m. During operation, the main circuit is often impacted by hundreds of amps to thousands of AMPS starting current or tens of thousands of AMPS short-circuit current, and the residual current transformer is in extreme saturation state. under these circumstances. The transformer shall not affect the action characteristics due to the residual magnetism generated by impulse current. Therefore, iron nickel soft magnetic alloy with high initial permeability, high maximum permeability and low coercivity is generally used as the core material of residual current transformer. Fe Ni soft magnetic alloy has very high initial permeability and maximum permeability, very low coercivity, low saturation flux density and good temperature stability.

:Both zero sequence current transformer and residual current transformer use the principle of electromagnetic induction to detect current; The vector operation of current signal can be realized by the superposition of magnetic field; Zero sequence current transformer is used to detect the vector sum of three-phase current, excluding zero line. If the three-phase is unbalanced, the zero sequence current transformer will have current. If the three-phase imbalance reaches a certain value, it can be protected; Residual current transformer mainly detects leakage current.In the three-phase system, the vector sum of three-phase and zero line is detected. In the single-phase system, the vector sum of live line and zero line is detected. Whether it needs to pass through the zero line depends on what current is detected by the transformer. Whether the detected current needs vector operation by a / B / C / N line.

If necessary, the magnetic field generated by the current shall be superimposed to realize the operation,If you don't need it, just go through the order.For example:

If only phase a current is detected, only phase a conductor needs to pass through the transformer.If the leakage current is detected in single phase, the leakage current is defined as live line current zero line current. Here, a vector superposition operation is done. Both live line and zero line need to pass through the transformer, and the entry direction needs to be correct.If the zero sequence current of three phases is detected, according to the definition, the zero sequence current is = A-phase current B-phase current c-phase current. Therefore, the conductor of a / B / C three phases needs to pass through the transformer, and the entry direction needs to be correct.

If the leakage current of three phases is detected, according to the definition, the leakage current = A-phase current B-phase current c-phase current n-line current. Therefore, the wires of a / B / C / N need to pass through the transformer, and the entry direction needs to be correct.