Abstract
Many building fires due to ignition of electrical wiring instruments have been reported. The ignition would be caused by electrical breakdown in insulation materials. The most common case of electrical breakdown is exothermic reaction. 150°C is caused due to the overload current and/or inferior electrical wire connection.
The Polyvinyl Chloride (PVC) is widely used as an insulating material in various electric products. The exothermic phenomenon may cause deterioration of insulating properties in PVC due to the chemical decomposition. Many researches reported about the relationship between the fire hazard due to the degradation of insulating properties, for example, tracking index and insulation resistance value. However, the research in viewpoint of volume resistivity in high temperature region up to 200°C has not been reported, because PVC melts and/or deforms when the temperature rises.
In this paper, conduction current has been measured while measuring thickness in the range from room temperature to 200°C under DC electric field in a heat-treated PVC sheet by using a developed high temperature space charge measurement system. It has been observed that the breakdown strength of the sheet strongly deteriorates in the range from room temperature to 90°C with 150°C-100 h (hour) heat-treated PVC, which is different from the results obtained with non-heat treated PVC and 100°C-300 h heat-treated PVC. The increase of conduction current is observed in the low temperature range before breakdown with 150°C-100 h heat-treated PVC. It shows that the heat treatment over 150°C deteriorates the breakdown properties in the range from room temperature to 90°C due to thermal decomposition and dehydrochlorination in PVC.
