The working principle of the zero-sequence current transformer of the AC current transformer: The basic principle of zero-sequence current maintenance 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. Under normal conditions of the line and electrical equipment, the vector sum of the currents of each phase is equal to zero. Therefore, the secondary winding of the zero-sequence current transformer has no signal output, and the implementation element does not operate.
When a ground fault occurs, the vector sum of the currents of each phase is not zero, and the fault current causes magnetic flux to be generated in the annular iron 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 act, driving the tripping device, switching the power supply network, reaching the ground fault maintenance attempt. Function: When electric shock or leakage fault occurs in the circuit, maintenance action will be taken and the power will be cut off.
Application: A CT current transformer can be installed on each of the three-phase lines, or the three-phase wires can be passed through zero-sequence current transformers together, or a zero-sequence current transformer can be installed on the neutral line N, and it can be used to detect Three-phase current vector sum.
1. The CT current transformer is different from the zero-sequence current transformer. The zero-sequence current transformer is used to detect the zero-sequence current. Generally, all the three fronts are passed through the inner hole of the transformer, and the vector sum of the three-phase current is measured, that is, the zero sequence current.
2. The characteristics of the zero-sequence current determine that under normal circumstances, the primary current of the zero-sequence current transformer is very small, but under abnormal conditions, the zero-sequence current will also be very large.
3. Since the zero-sequence current transformer generally passes through three fronts, under the same primary current, the inner hole of the zero-sequence transformer is larger. "Inner hole diameter" is an important target of zero-sequence transformer.
4. The accuracy level is lower. In daily life, we don't often see the current transformer, but it covers a lot of places, and its existence is indispensable. As a special transformer, the current transformer works similarly to the transformer. The difference is that in the iron core of the transformer, the alternating main magnetic flux is generated by the current of the mutual voltage applied at both ends of the primary winding. The alternating main magnetic flux in the iron core induces the corresponding secondary electromotive force and secondary current in the secondary winding of the current transformer.
Since the primary winding and the secondary winding of the current transformer are made in the same iron core, they are linked by the same main alternating magnetic flux, so the current and turns product of the primary winding and the secondary winding should be equal in value.
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