What is zero sequence current? What is zero sequence transformer in switch cabinet? What does it do?

What is zero sequence current?

In a three-phase four-wire circuit, the phasor sum of the three-phase current is equal to zero, i.e. 1a+ B +IC-0 if a current transformer is connected to the three-phase four-wire circuit. The induced current is zero. When electric shock or leakage fault occurs in the circuit, leakage current flows through the circuit, then the phase-sum of the three-phase current passing through the transformer is unequal zero, and the phase-sum is: 1 + 1 b + 1 c - () leakage current in the transformer secondary coil has an induced voltage, the voltage on the detection part electronic amplifier circuit, compared with the scheduled reserve device current value, such as greater than the current action, even sensitive relay action, acting on the components of the transformer tripping here receive called zero sequence current transformer, three phase current phasor And is not equal to zero, the resulting current is zero sequence current.

What is zero sequence transformer in switch cabinet? What does it do?

Principle: The basic principle of zero-sequence current protection is based on Kirchhoff's current law: the algebraic sum of complex currents flowing into any node in the circuit is equal to zero. Under the normal condition of the circuit and electrical equipment, the vector sum of each phase current is equal to zero. Therefore, the secondary winding of the zero-sequence current transformer has no signal output and the executive element does not operate. When a grounding fault occurs, the vector sum of each phase current is not zero. The fault current causes magnetic flux in the annular core of the zero-sequence current transformer. The inductive voltage on the secondary side of the zero-sequence current transformer makes the actuator move, drives the tripping device, switches the power supply network, and achieves the purpose of grounding fault protection. Function: when an electric shock or leakage faults in the circuit, protection action, to cut off the power supply use: can be on the three phase line and a current transformer, or let sequence current transformer three-phase wire together through the season, can also be installed on the neutral line N a zero sequence current transformer, current vector, and using it to detect three-phase. The zero-sequence transformer is used to detect "unbalanced" current (leakage current) through the transformer's main circuit, because on the main circuit path through the transformer, the current should come out of the power supply and pass through one of the transformer's lines to the electrical equipment (load). And then the load comes back through the other lines that go through the transformer and then back to the power source, and the amount of current that goes through the transformer should be "equal", that is, the same amount, but in a different direction. Because of the same size in the opposite direction of current after the transformer primary side (main circuit line is considered to be a primary side of transformer), not in the secondary side induction current to or electrical signals to (electromagnetic induction in the opposite direction due to the same size and cancel each other out), and so on the zero sequence current transformer, there is no signal output. If one of the main return route road route after out of the power supply side on the current after the transformer primary side ", is no longer the other transformer primary side line or incomplete the other transformer primary side line back to the power supply side, but through other channels "" back to the power supply side, then you can make the secondary side of transformer (transformer coil) induction out of this The current signal of "passing without returning" (such as shock of human body or leakage of equipment) of the transformer can be amplified to control the action of the protective equipment connected with the zero-sequence transformer, disconnect the power supply of the protected master to ask the way, and ensure the safety of human body and equipment.