AC and Lightning Impulse Breakdown Voltage of Natural Ester Impregnated Pressboards

The paper represents AC and lightning impulse (positive and negative impulse) breakdown voltage characteristics of natural ester impregnated pressboards with different impregnation period. The pressboard specimen was prepared as a rectangular shape (the length and the width are 120 mm as well) and thickness dimension of the pressboard in the experiment was approximately 1.6 mm. The pressboards were dried up in the vacuum oven with temperature at 80°C for 12 hours under 200 mbar pressure. In addition, these pressboards were divided into 3-group according to the impregnation periods. The 1st group, the pressboards were impregnated with natural ester at 60°C for 8 hours under 200 mbar pressure. The 2nd and 3rd group, the pressboards were impregnated at 60°C for 16 and 24 hours, respectively, under 200 mbar pressure-controlled conditions. The plane-plane electrodes inserted with the specified number of the pressboard specimens were prepared. These electrodes were installed in the test cell filled with the natural ester. A 24 kV AC Voltage was applied to the test cell for 3 months. At the end of the first month, half of the pressboard samples was token from the test cells. Then, the AC breakdown voltage and impulse breakdown voltage characteristics of the impregnated pressboard were investigated in accordance with IEC 60243-1 and IEC 60243-3, respectively. At the end of the third month, another half of the pressboard samples was token from the test cells to perform AC and lightning impulse breakdown voltage test also. From the test results, all pressboards which are impregnated for a long period provided higher AC breakdown voltage than the pressboard which are impregnated for a short period. In the other hand, the impulse breakdown voltage values of each condition are not very different. Obviously, the period for impregnation significantly affects the AC breakdown characteristic of the natural ester impregnated pressboard. On the otherwise, it is not affecting the impulse breakdown characteristic of the natural ester impregnated pressboard.