Study of Thermal-runaway tests on Insulators subjected to DC voltages

The failure of insulators under DC voltages is due to various factors like thermal runaway, ion migration, anode growth, surface erosion, cement growth etc... However, the rate of failure is higher in polluted zones where surface erosion and puncturing of insulators due to ion migration can occur. Therefore, insulators have to be subjected to accelerated ageing tests to simulate ion migration and to check their capability to withstand the stresses. Thermal runaway is also an important test. By carrying out thermal runaway test at higher temperature, it may be possible to identify the good insulators. This paper presents the work carried out in order to find the quality of DC insulators by thermal runaway tests and the measurement of the body resistance of the insulators. The voltage and temperature were varied during these tests in order to clearly differentiate the quality of insulators. The result will be useful for the design of insulators for the HVDC transmission system.