The basic principle of zero-sequence current transformer protection 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 line and electrical equipment are normal, the vector sum of the phase currents 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 the phase currents is not zero. The fault current generates magnetic flux in the ring core of the zero sequence current transformer. The trip device switches the power supply network to achieve the purpose of ground protection.
Function: When an electric shock or leakage failure occurs in the circuit, the protection action will be performed and the power supply will be cut off. Use: You can install a current transformer on each three-phase line, or pass the three-phase line through a zero-sequence current transformer, or install a zero-sequence current transformer on the zero line N to detect the sum of three-phase current vectors . In a three-phase four-wire circuit, the sum of the phasors of the three-phase current is equal to zero, that is, Ia + Ib + IC = 0. If the current transformer is connected to a three-phase four-wire system, the induced current is zero. When an electric shock or leakage fault occurs in the circuit, the leakage current will flow in the circuit. At this time, the phasor of the three-phase current flowing through the transformer and the unequal zero is the sum of the phasors: Ia + Ib + Ic = I (leakage current) In this way, the induced voltage transformer coil will be induced in the secondary current. This voltage is applied to the electronic amplification circuit of the detection section and compared with the predetermined operating current value of the protection zone device. The relay is activated and the actuator trips. The transformer connected here is called a zero-sequence current transformer. The sum of the phasors of the three-phase current is not equal to zero, and the generated current is zero-sequence current.https://www.ctsensorducer.com/