In order to clarify the relationship between temperature distribution on insulator surface and dry band as well as dry band arc

we established a distribution equation of temperature on insulator surface based on studies of heating model of wet contaminated insulator and heat transfer theory. Moreover

we studied influence rules of factors such as surface resistivity

spread voltage

wind and material on the temperature distribution. Temperature difference among porcelain insulator with contamination degree of Ⅳ reaches 7.2 ℃. The forming condition of dry band is obtained based on studies of temperature distribution

relationship between evaporation rate and temperature

hygroscopicity of contamination. Furthermore

taking surface resistivity

spread voltage

wind speed and altitude into account

we studied the formation regularity of dry band and studied

the forming condition and critical voltage of dry band arc by analyzing relationships among spread voltage

dry band voltage

and residual contamination layer voltage. Critical voltage of dry band arc reaches 20 k V when the width of dry band increases from 1 mm to 8 mm. Dry band is easy to form with conditions such as high local temperature

high altitude

large difference between saturated vapor pressure and water vapor pressure. It is more easier to form a dry band arc under both high humidity and breezeless environment. Above research findings improve the theory of external insulation flashover

and provide theory evidences for insulator design and flashover prevention.