What is the zero sequence transformer in the switchgear? what's the effect? -Solutions - Huaqiang Electronic Network

inductance

Principle: The basic principle of zero-sequence current protection 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 normal line and electrical equipment, the vector sum of the currents of the phases is equal to zero. Therefore, the secondary winding of the zero-sequence current transformer has no signal output, and the actuator does not operate. When the 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 of the zero-sequence current transformer causes the actuator to act, driving The tripping device switches the power supply network to achieve the purpose of ground fault protection.
Function: When an electric shock or leakage fault occurs in the circuit, the protection action is taken and the power is cut off.
Use: can install a current transformer on each of the three-phase lines, or let the three-phase wires pass through a zero-sequence current transformer together, or install a zero-sequence current transformer on the neutral line N to detect Three-phase current vector sum.
Zero-sequence transformers are typically used to detect "unbalanced" current (leakage current) on the main circuit loop through the transformer because the current should be from the main circuit line that passes through the transformer. The power supply comes out, passes through a line in the transformer to the power device (load), and then returns from the load through the other line through the transformer to the power terminal. The magnitude of this current should be "passed by the transformer." The same amount is the same size, but the direction is different. Because the current of the same magnitude and opposite direction passes through the primary side of the transformer (the main circuit can be regarded as the primary side of the transformer), no current or electrical signal is induced on the secondary side (electromagnetic induction due to its The same size and opposite directions cancel each other out, so there is no "signal output" on the zero-sequence transformer.
If the current on one of the main circuit lines passes the "primary side" of the transformer after coming out of the power supply terminal, it does not pass through other lines on the primary side of the transformer or does not completely pass through other lines on the primary side of the transformer. Returning to the power supply end, but returning to the power supply terminal through other "pathways", the secondary side of the transformer (the transformer coil) senses the current signal "passing back without going back to the transformer" (such as The human body is electrically shocked or the device is leaking.) After this signal is amplified, it can control the protection device that is electrically connected to the zero-sequence transformer, and disconnect the power supply of the protected main circuit to ensure the safety of the person and equipment.