Stability and Long Term Degradation of Metal Oxide Surge Arresters

The thermal runaway process and the long term degradation of metal oxide blocks for a surge arrester are investigated both experimentally and analytically. The critical condition of a thermal runaway of the blocks is formulated. The dynamic stability after surge absorptions is also studied. The stability limit is given as a function of the temperature rise of the blocks due to the surge absorptions. A kind of degradation of metal oxide proceeds under ac stress even at the level lower than that required for the thermal runaway. The life of a metal oxide surge arrester is evaluated combining the degradation process with the above thermal runaway condition. The Arrhenius relation which has been proposed to evaluate the life of metal oxide blocks is discussed in the light of the analysis.