The zero phase current transformer can be set as appropriate during operation, so that the zero-sequence current when the ground fault occurs can be detected, so that the faulty circuit can be cut off, and the IT system is generally used for reliable power supply. The three-phase three-wire distribution line that does not need to be neutralized in the industrial and mining enterprises that need to send off the power supply circuit immediately, but need to issue the insulation damage monitoring signal to maintain the power supply for a period of time.
When the zero phase current transformer is single-phase grounded during operation, the zero-sequence current flowing through the faulty line is the sum of the capacitance of the system-wide faulty system, so it is easy to detect the ground fault current, so zero-sequence current protection can be used. The device monitors the relatively first ground fault.
The TT grounding system of zero phase current transformer is often used in the three-phase four-wire power distribution system of industrial and agricultural, civil building lighting and power hybrid power supply. It is often found that the three-phase unbalanced current is large, when one phase is grounded. The Id loop impedance includes phase line impedance Z1, PE line impedance ZPE, load side grounding resistance RA and power side grounding resistance RB, contact impedance Zf, ie ZS=Z1+ZPE+RA+RB+Zf, ground fault current Id=220 /ZS, due to RA+RB>>Z1+ZPE+Zf, and the RA+RB values are generally large, it is obvious that the fault loop impedance of the TT system is large, and the single fault current Id generated is much smaller than the unbalanced current. It is difficult to detect the fault current, so it is not suitable for the TT grounding system.