A Multistage Dry Insulated Current Transformer

The insulation method of traditional electromagnetic current transformers (CTs) is single-stage insulated, and the insulation materials include oil, SF6 gas, polytetrafluoroethylene (PTFE) film, and epoxy resin. It has to deploy multiple capacitive screens for voltage equalization to improve the electric field distribution, which results in complex insulation structure and high cost. A multistage dry insulated CT for measurement is proposed in this article, which is composed of multistage CTs in series and insulated by epoxy resin, so the line voltage is shared by the multistage CTs. Therefore, a five-stage prototype CT is analyzed and designed, and the structure, the measurement principle, the electric field distribution, the technical characteristics, and the error calculation and compensation of this CT are explored. The results show that the proposed dry CT meets the 0.2S class accuracy and has advantages of low insulation cost, high safety, environmental protection, and so on.