Abstract: The technical performance of a novel insulated capacitive voltage transformer is described, demonstrating the success of its research and development. Keywords: Capacitive voltage transformer, Ferromagnetic resonance, Partial discharge, Temperature rise 1 Introduction The research project on this novel insulated capacitive voltage transformer is a key technology project of Guangxi Zhuang Autonomous Region. After research and trial production, the product has passed the technical appraisal of Guangxi Zhuang Autonomous Region. This capacitive voltage transformer adopts a novel insulation structure, namely, a dry-type electromagnetic device. It has the following technical and economic characteristics: 1.1 The electromagnetic unit is first insulated and then protected with slightly positive SF6 gas. 1.2 Good anti-leakage effect, with an annual gas leakage rate of less than 0.05%, and almost no gas replenishment is required during the product's service life. 1.3 The electromagnetic unit has no risk of oil leakage, eliminating the need for annual inspections such as oil sample testing. 1.4 Because the electromagnetic device is gas-filled, oil treatment time can be saved, thereby shortening the product's production cycle and improving working conditions. 1.5 Provides technical support for the development of capacitive voltage transformers for GIS. 2. Main Research Contents 2.1 Product Performance Indicators 2.1.1 The main performance indicators of the product are shown in Table 1. 2.1.2 The tanδ of the capacitive voltage divider of the product is ≤0.10%, and the capacitance deviation does not exceed ±5% of the rated value. 2.1.3 The winding connection group of the intermediate voltage transformer is 1/1/1-12-12. 2.1.4 The annual gas leakage rate of the product should not exceed 0.5%. 2.1.5 Other performance characteristics of the product shall comply with the relevant technical requirements of GB/T4703-2001 "Capacitive Voltage Transformers" and JJG314-1994 "Voltage Transformers for Measurement". 2.1.6 The product's appearance and structural diagram are shown in Figure 1. 2.2 Withstand Voltage Performance Since the electromagnetic device is first insulated, it passed the withstand voltage test even with an SF6 gas pressure of 0.1MPa, therefore the insulation strength meets the requirements. 2.3 The performance of the ferroresonant capacitive voltage transformer depends on the quality of its ferroresonant performance; therefore, a relatively detailed study was conducted. Since the insulation strength of the electromagnetic device meets the technical requirements, experimental studies were conducted under SF6 pressure of 0.1–0.2 MPa. With proper damper parameter matching, the ferroresonant test was passed at 0.1 MPa pressure. However, with improper damper parameter matching, even if resonance was effectively suppressed, the high transient overvoltage led to internal discharge within the electromagnetic unit at 0.2 MPa pressure or even higher. 2.4 Partial Discharge Performance Partial discharge performance is a key focus of research on capacitive voltage transformers with novel insulation structures. SF6 pressure needs to reach above 0.3 MPa for its performance to be comparable to transformer oil. Therefore, the electromagnetic device must first undergo insulation treatment, and internal pressure equalization measures were implemented. At SF6 pressure of 0.2 MPa, the partial discharge of the electromagnetic device was 2–6 pC; when the pressure dropped to 0.12 MPa, the partial discharge was still 2–6 pC; and when the SF6 pressure was less than 0.12 MPa, the partial discharge was 10–50 pC. 2.5 Temperature Rise GB/T4703-2001 "Capacitive Voltage Transformers" specifies the following: a) With the secondary winding connected to the rated load and the residual voltage winding unloaded, apply 1.2 times the rated voltage for continuous testing until the temperature stabilizes. The temperature rise of each winding should not exceed 60℃. b) After the electromagnetic unit reaches a stable state under the 1.2 times rated voltage test in item a), immediately apply 1.5 times the rated voltage for 30 seconds. The temperature rise of each winding should not exceed 70℃. c) Under the above test conditions, the temperature rise of the core and other metal surfaces of the electromagnetic unit, and the top layer of oil, should not exceed 70℃. The heat dissipation of new insulation structure electromagnetic devices differs from that in oil. Measures such as reducing current density and increasing heat dissipation surface are adopted to ensure that the temperature rise of the product does not exceed the standard specified value. Under the three test conditions (a), (b), and (c), the temperature rise at each point does not exceed 12℃. 2.6 Gas leakage rate was tested using an HL-108 leak detector according to the method specified in GB11023-1989, and the annual leakage rate was 0.05%. 2.7 Accuracy [align=center]The accuracy test results are shown in Table 2.[/align] 3 Conclusions 3.1 The technical requirements of the new insulation structure capacitive voltage transformer, including ferroresonance, partial discharge, temperature rise, accuracy, and leakage rate, meet the requirements of the corresponding standards or technical conditions. 3.2 After insulation treatment, the partial discharge of the electromagnetic device did not change significantly and was less than 10 pC when the SF6 gas pressure was in the range of 0.12–0.2 MPa; the maximum partial discharge was 50 pC when the SF6 gas pressure was less than 0.12 MPa. 3.3 The electromagnetic device can still meet the insulation performance requirements for operation when the SF6 gas pressure is 0.1 MPa.