one form of high voltage insulator failure is flashover phenomenon that can cause problems in the performance and reliability of overhead lines. Main reasons of changing the electrical behaviour of the insulators and their incomplete performance are pollution and humidity of the environmen Pollution also reduces the efficiency of the insulators and increases the possibility of flashover occurrence which consequently results in transmission line outage. Therefore forecasting the flashover and detecting critical conditions are very important. In this paper, we proposed a new model for polluted insulators flashover according to the new electrical equivalent circuit which is chosen based on obtained experimental results. Also this paper expresses that, arc constants (n and N) are not static but related on the geometry and intrinsic parameters of the insulator pollution and heat insulator surface that depends on mathematical equation models. Critical parameters of the proposed model such as critical voltage, critical current and critical arc length are presented based on mathematical equation calculations and determinations. Proposed model in this paper is able to predict complete arc polluted insulators
