Short-Term and Long-Term Dielectric Characteristics of Molded Compound According to Various Portion of Alumina Trihydrate Micro-Filler

The demand on electric power is expected to increase continuously due to the development of industry and the congestion of cities which requires large capacity and high voltage transmission for electric power system. In addition, electric power of good quality, compacted electric power device, reliable and secure electric system are also required. For these reasons, solid insulation materials are preferred due to its advantage on size reduction and weight lightening. Solid dielectric materials improve the electric breakdown strength by suppresses the initiation and propagation of breakdown. However, the characteristics of solid dielectric materials are apt to influenced by operation voltage, period of use and the condition of internal solid insulation material. Especially, the internal deterioration of solid dielectric due to the increment of operation period in rated voltage condition could cause breakdown of the electric power apparatuses. In this paper, short term and long-term breakdown tests for Bulk Molded Compound (BMC) with various portion of Alumina Trihydrate (ATH) micro filler were carried out to find out the dielectric performance of solid dielectric introduced in Vacuum Circuit Breaker (VCB) product. The long-term breakdown test corresponds to consideration of the operation voltage of VCB to establish the lifetime and insulation reliability of dielectric material. The short-term breakdown tests were conducted in mineral oil with sphere - sphere electrodes for BMC with 0, 25, 40% of ATH. The long-term breakdown test was carried out for the voltage level of 3, 5, 10% of one - minute step - up tests based on the results from the short test breakdown test and the comparison analysis on the time to breakdown has been performed. From the test results, the breakdown voltage of BMC with 25% of ATH specimen was increased compared to specimen with 0% one, and the breakdown voltage of BMC with 40% ATH specimen was slightly higher than 25% one. In case of long term breakdown test, the time to breakdown was reduced in case of BMC with 40% ATH compared to 25% one.