The zero-sequence current transformer is used in conjunction with relay protection devices or signals when generating zero-sequence grounding current in the power system, enabling the device components to actuate and achieve protection or monitoring.

For the specific application of zero-sequence current protection, a current transformer (CT) can be installed on each of the three-phase lines, or the three-phase conductors can be passed through a zero-sequence CT together. Alternatively, a zero-sequence CT can be installed on the neutral line N. These C.Ts are used to detect the vector sum of the three-phase currents, which is the zero-sequence current Io, as expressed by IA+IB+IC=Io. When the three-phase loads connected to the line are completely balanced (without grounding faults, and leakage currents from the line and electrical equipment are not considered), 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 phase experiences a grounding fault, a single-phase grounding fault current Id is inevitably generated. At this time, the detected zero-sequence current IO=IN+Id, which is the vector sum of the three-phase unbalanced current and the single-phase grounding current.

The installation of the integrated current transformer should be carried out before laying the cable, which will pass through the transformer during the cable laying process.

Open-type current transformers are not limited by whether cables are laid or not. The specific method is as follows:

(1) Remove the connecting pressure plate of the transformers "K1ˊ" and "K2ˊ" (this requirement does not apply to circular transformers).

(2) Loosen and remove the two hexagonal socket bolts on the top of the transformer (for circular transformers, loosen and remove the fastening screws on both sides), and the transformer will be divided into two parts.

(3) Place the transformer over the cable, clean the contact surface, apply a thin layer of anti-rust oil, align the two parts of the transformer, and tighten the hexagonal socket head cap screws (fastening screws on both sides). The two parts of the transformer should be aligned to avoid affecting performance.

(4) Fix the connecting piece on "K1ˊ" and "K2ˊ" (this requirement does not apply to circular current transformers).

(5) When installing transformers with an inner hole diameter greater than 120mm horizontally, please add a non-magnetic support.