Zero sequence current transformer action principle

Zero sequence current protection is generally suitable for use in TN grounding system. Because when occurs a phase to ground when the TN-S system Id loop impedance including the phase line impedance Z1, PE line impedance ZPE and contact impedance Zf, ie Zs = Z1 + ZPE + Zf; For TN-C system, Id loop impedance including the phase

Line impedance Z1, PEN line impedance ZPEN and contact resistance Zf, ie ZS = Z1 + ZPEN + Zf; For TN-CS system, Id loop impedance including the phase line impedance Z1, PEN line impedance ZPEN, PE line impedance Zf ZPE and contact resistance , the ZS = Z1 + ZPEN + ZPE + Zf, can generate a single-phase

Ground fault current Id = 220/ZS, no larger than a three-phase fault current imbalance, as long as the appropriate setting, you can detect a ground fault occurs zero sequence current in order to cut off the fault circuit. The IT systems are generally used for power supply reliability is higher

For single phase power supply Circuit breaker immediately cut unnecessary, but need to send insulation damage monitoring signal to maintain continued supply of industrial and mining enterprises for some time within the unworthiness of the neutral phase three-wire distribution lines. When single-phase ground when flowing through the fault line zero sequence

Current system-wide non-fault system capacitive currents, which can easily detect the ground fault current, it can be used zero-sequence current protection device to monitor the relative first ground fault. TT earthing system is often used in industry, agriculture, civil lighting, power supply mix

Three-phase four-wire power distribution system, often find the three-phase current imbalance greater when the event of a phase to ground, Id loop impedance including the phase line impedance Z1, PE line impedance ZPE, load side grounding resistors RA and power side grounding resistor RB, contact impedance Zf, ie

ZS = Z1 + ZPE + RA + RB + Zf, the earth fault current Id = 220/ZS, the RA + RB >> Z1 + ZPE + Zf, and RA + RB values ??are generally larger, it is clear ring system failure TT Road impedance of the resulting single-access fault current Id, far less than the current imbalance is difficult to check

Measure the fault current, it does not apply to TT earthing system.
For the zero-sequence current protection zero sequence CT installation process must comply with the relevant standards. For IT earthing system, as a result of single-phase ground fault, earth fault currents may not only along the cable back into the surface of the conductor, but also could not fault along the cable

The conductor surface flow back, it must be installed by the cable head to ground zero sequence CT, so as to ensure the faulted phase and non-fault phase current through the ground capacitance, which can prevent external fault protection device malfunction, but also to ensure failure device reliable action. For

IT earthing system, generally installed on the neutral line N zero sequence CT, on the low pressure side of the zero-sequence CT busbar must be installed in the neutral line N and the work of ground (or repeating ground) between the busbars. Such as zero-sequence CT installed in the N line distribution panel busbars, power distribution panel as gold

Metal enclosure generally associated directly with the ground electrode, when the bus is shorted to ground occurs, the resulting fault current Id of the metal shell along the distribution screen → → ground current electric transformer neutral point, without passing through the zero-sequence CT, reach The demands of the protection function, which is in

When the construction site is easy to neglect.