Effect of temperature on the electrical breakdown of conductor samples in R-Temp and Envirotemp

Both a.c. and impulse breakdown voltages have been measured over a range of temperatures from 30 °C to 180 °C using lengths of commercial conductor insulated with cellulose or Nomex 410 tape and immersed in two low-flammability liquids, R-Temp and Envirotemp. The insulated conductors were tested either touching or with a 1 mm liquid gap between them. Impulse breakdown voltages for zero gap were found to fall progressively as temperature rose from 30 °C to 180 °C whereas for cellulose under alternating voltages there was effectively no variation whatever. With a 1mm liquid gap between the surfaces of the insulation the alternating breakdown voltages declined in Envirotemp at 130 °C and 180 °C but did not do so in R-Temp. This is likely to be caused by gas evolution in Envirotemp.