The energy injected into the gaseous environment by the discharge will increase the
temperature of the gas in the local vicinity. In turn, this thermal differential will cause
the gas molecules in the hotter region to migrate to the cooler regions. Although
attempts have been made to ascertain the gas temperature under partial discharging
[6], in general these results must be treated with caution. In addition, the combinations
of particle input energy transfer, chemical bond restructuring and other potentially
exothermic reactions will result in temperature increases at a discharging surface.
The author’s personal experience has suggested that the thermal stress created by a
partial discharge may be sufficient to cause damage to polymeric materials but not to
other forms of solid insulating material. Even in the case of polymers, the degradation
sustained due to thermal stressing alone is likely to be insignificant compared with
other stresses present. However, since the degradation is due to a synergetic interaction
of a number of stresses, it must still be considered where partial discharges are present.
The reaction of polymeric materials to a purely thermal stress is dependent on the
structure of the material [1].
For example, simple structures, such as polyethylenes, degrade by random chain scission: