Zero sequence current transformer: features: in line with GB1208 standard; design of ring current transformer; casting structure of epoxy resin; electromagnetic induction; not affected by climate; when the power grid works normally, there is no signal input in the secondary circuit and the energy loss is small, which increases the service life of components and improves the reliability of the product. When the fault occurs, the output signal drives the tripping device and switches the power supply network to achieve the purpose of ground fault protection.