Zero Sequence Current Transformer

Zero sequence current transformers are used in conjunction with relay protection devices or signals to activate device components and achieve protection or monitoring when generating zero sequence grounding currents in power systems. Zero sequence current transformer is a single turn through type current transformer, generally used in power protection equipment such as small current grounding line selection devices, microcomputer harmonic elimination devices, etc. When an electric shock or leakage fault occurs in the circuit, the secondary side of the transformer outputs zero sequence current, causing the protection of the equipment on the connected secondary line to act (such as cutting off power, alarm, etc.). The specific application of zero sequence current protection can be to install a current transformer (CT) on each three-phase line, or to pass the three-phase wires through a zero sequence CT together, or to install a zero sequence CT on the neutral line N. These C T is used to detect the current vector sum of the three phases, that is, the zero sequence current Io, IA+IB+IC=Io. When the three-phase loads connected to the line are completely balanced (without grounding faults and without considering the leakage current of the line and electrical equipment), Io=0; when the three-phase loads connected to the line are unbalanced, Io=IN, and the zero sequence current at this time is the unbalanced current IN; When a grounding fault occurs in a certain phase, a single-phase grounding fault current Id is inevitably generated. At this time, the detected zero sequence current IO=IN+Id is the vector sum of the three-phase unbalanced current and the single-phase grounding current.