Can ordinary current transformers be used as residual (zero sequence) current transformers

Ordinary current transformers can convert large currents with larger values into secondary currents with smaller values for protection, measurement, etc. The function of the residual (zero-sequence) current transformer is to protect and cut off the power supply when an electric shock or leakage fault occurs in the circuit. These names are very similar, but the roles are very different. What is the difference and function? There is no problem in principle to use cardioid current transformers as zero-sequence transformers, but their sensitivity is completely different.

The basic principle of residual (zero-sequence) current transformers is based on Kirchhoff's current law: the algebraic sum of the complex currents flowing into any node in the circuit is equal to zero. In the case of ordinary lines and electrical equipment, the vector sum of the 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 work. When a ground fault occurs, the vector sum of each phase current is not zero. The fault current causes magnetic flux to be generated in the toroidal core of the zero sequence current transformer, and the secondary side induced voltage transformer of the zero sequence current causes ) The current transformer acts to drive the trip device to switch the power supply network to achieve the purpose of ground fault protection.

Ordinary current transformers can convert large currents with larger values into secondary currents with smaller values for protection, measurement, etc. For a current transformer with a ratio of 400/5, the actual current of 400A can be converted to 5A.

The current transformer can be installed on each three-phase line, or the three-phase wires can pass through the zero-sequence current transformer together, or the residual (zero-sequence) current transformer can be installed on the neutral line N, and the three-phase current transformer Can be used to detect three phases. The current vector sum.

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