The obtain expected dielectric property under cryogenic temperature, bisphenol A epoxy resin is modified by adding liquid hardener (M-phenyldimethylamine) and alumina particles. In the modified bisphenol A epoxy resin system, alumina is used as filler. The diameters of filler used were 50 um, and the mass content of filler are 10% and 20%. After de-gassing had been done under vacuum for an hour, the modified bisphenol A epoxy resin system is cured under 100℃ for 120 minutes. then, the bisphenol A epoxy resin is cooled to room temperature under natural conditions.
5.2. Experimental method
The experimental method of permittivity was according to ASTM-D150 , the dimension of the sample is manufactured to the dimension of 10*5*2 mm, as shown in Fig. 13, the insulating sample is bonded with two metal electrodes, the distance between the two metal electrodes is 2 mm. It was observed by a microscope that there is no voids or cracks around the electrodes, the sample is tested by GLMSTD-A dielectric constant tester and the test is performed in the solid state institute of Chinese Academy of Sciences.
5.3. Experimental result
The permittivity of insulation material is calculated by formula (2).
The dimension of the samples are listed in Table.3
5.4. Electrical performance tests
The manufacturing process of glass fiber reinforced bisphenol A epoxy resin composite was finished under vacuum to reduce void defect, and the electrical performance is tested by high voltage generator in the Institute of Plasma Physics, Chinese Academy of Science. 50 thermal cycling tests between room temperature and liquid nitrogen temperature are performed for the 19 kV class SD , as shown in Fig. 14.
After the thermal cycling tests had been done, the leakage current test is performed with high voltage generator made by Shanghai Juter, the DC voltage is set at 10 kV, 13 kV, 16 kV, and maintained for 1 minute, then it raised to 19 kV and maintained for 3 minutes, the peak leakage current is below 1µA, as shown in Fig. 15.
Partial discharge test is performed with pulse current method , as shown in Fig. 16. The voltage is set at 5 kV AC and maintained for 5 minutes, the discharge quantity is less than 100 pC, which indicate that the electrical property of the 19 kV class SD is in good condition after thermal cycles, as shown in Fig. 17.
Paschen tests is performed between wires and ground insulation in helium gas with 99.99% purity to analyze the quality of insulation of ITER HV SD to extend the research on Paschen's law under various conditions . the DC voltage is firstly gradually increased to 19 kV and maintained for 5 minute. The test pressure was 1 Pa, 10 Pa, 100 Pa, 1 kPa, 10 kPa and 50 kPa, and the peak leakage current is less than 10 µA, as shown in Fig. 18.