Electric Strength of Small Creepage Distances under Natural Environmental Conditions

The electric strength of insulating configurations of solid insulating materials mainly depends on the contamination of the creepage distance, the formation of creepage paths on the insulating material by creepage currents, and the micro-climate on the insulator surface. For the intended smaller and more precise dimensioning of insulation configurations for low voltage equipment, exact knowledge about the influence of these factors on the withstand voltage is necessary. Therefore test specimens which are made from insulating materials with different comparative tracking index were investigated. The test specimens have been exposed for some months under natural environmental conditions. During the period of exposure they were connected to ac or dc voltages in the 10 to 660 V range. The laboratory measurements of the withstand voltage are carried out with impulse voltage of the shape 1.2/50 μs under well-defined climatic conditions. According to the measured withstand voltages, new dimensioning rules for creepage distances are proposed.