Protection principle and protection action of zero sequence current transformer

- May 04, 2019-

The zero sequence current transformer is used in conjunction with the relay protection device or signal when the power system generates zero-sequence ground current during use, so that the device components operate to achieve protection or monitoring. When the zero-sequence current transformer operates, when an electric shock or leakage fault occurs in the circuit, the secondary side of the transformer outputs zero-sequence current, so that the equipment on the connected secondary line protects (cuts off the power, alarms, etc.) .

Protection principle of zero sequence current transformer

The zero sequence current transformer can be used in each phase to install a current transformer on the three-phase line. When operating, or let the three-phase wire pass through the zero sequence CT together, a neutral line N can also be installed. Zero-sequence CT, using these CTs to detect the current vector sum of three phases, ie zero-sequence current Io, IA+IB+IC=Io, when the three-phase load connected to the line is fully balanced (no ground fault, and not considered Leakage current of line and electrical equipment), Io=0; when the three-phase load connected to the line is unbalanced, Io=IN, the zero-sequence current at this time is the unbalanced current IN; when a phase has a ground fault A single-phase ground fault current Id is inevitable, and the detected zero-sequence current IO=IN+Id is the vector sum of the three-phase unbalanced current and the single-phase ground current.

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