The proposed nonlinear conductivity model representing thermal radiation is evaluated against the surface-to-surface radiation module provided by COMSOL Multiphysics.
An arrester slice including the air gap is modeled. The scenario is as follows. The ZnO block is preheated to typical arrester column temperatures after an operating duty. The ambient temperature is Tamb = 293 K. The ZnO block cools down via radiative heat transfer over the air gap to the porcelain housing.
Fig. 3(a) shows that the temperature within the ZnO block decreases over time. A very good agreement between both models is obtained [see Fig. 3(b)]. The relative deviation is always below 0.24%. The deviation reaches the highest values within the first hour, which is attributed to the involved heat capacities of the ZnO and the porcelain material.
Consequently, the nonlinear equivalent material model is considered suitable for modeling radiative heat transfer for long annular cylinders, such as air gaps of porcelain housed station
class arresters.