Feasibility study on substitution of SF6 insulated current transformer with environment-friendly natural gas

Abstract

Many SF6 gas-insulated current transformers (CT) are used in the power grid. The global warming potential (GWP) of SF6 is 23,900 times that of CO2, and the leakage of SF6 will aggravate the global warming trend. It is a hot issue to carry out the study of environment-friendly gas substitution in the power grid. This paper systematically studied the voltage withstand, partial discharge, and temperature rise characteristics of dry air, N2, and CO2 gas-insulated CTs. Through the study, the permissible critical pressures in environment-friendly gas-insulated CTs were determined to be 0.9 MPa for dry air, 0.7 MPa for N2, and 0.8 MPa for CO2, respectively. The partial discharge intensity was less than 5 pC for environment-friendly gas-insulated CTs at 0.3 MPa∼0.8 MPa pressure. The experimental results of temperature rise characteristics showed that under the condition of a 600A rated operating current, the maximum temperature rise of the CTs was about 80 °C, and the maximum temperature rise happened at the conductive rod. The experimental results verified that environment-friendly gases could meet the requirements of insulation and temperature rise. Due to the increase of pressure in CTs, the action pressure of the explosion-proof membrane should be changed to meet the mechanical strength requirements. It is recommended that when using 0.9 MPa dry air, the action pressure should be designed as 1.8 MPa; when using 0.7 MPa N2, the pressure should be designed as 1.4 MPa; when using 0.8 MPa CO2, the pressure should be designed as 1.6 MPa. The results of this paper can provide a reference for development of environment-friendly gas-insulated CTs.