The basic principle of zero sequence current maintenance is based on Kirchhoff's current law: the algebraic sum of the complex current flowing into any node in the circuit is equal to zero. When the circuit and electrical equipment are normal, 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 performance component does not operate.
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 induced voltage on the secondary side of the zero-sequence current transformer causes the performance element to act and drive Tripping equipment, switching the power supply network, to achieve the purpose of ground fault maintenance. Function: When an electric shock or leakage occurs in the circuit, the maintenance action is to cut off the power supply.
Use: 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, and use it to detect Vector sum of three-phase currents.