Analysis of the electro-thermal characteristics of MOA with average power equivalent method by incorporating stray capacitance

The voltage distribution across the varistor blocks of metal oxide arrester (MOA) becomes non-uniform due to stray capacitance which imposes greater electrical stress on varistor block located near the high-voltage electrode. Consequently, the upper varistor blocks undergoes greater thermal stress during operation, resulting in accelerated aging. An enhanced wide-range MOA model incorporating stray capacitance is proposed in this paper to accurately characterize the electrical behavior of the arrester. By integrating the circuit model with the electro-thermal model through the average power equivalent method (APEM), APEM effectively solves the challenge of computational resources due to time-varying excitations. Experiment is conducted to validate the accuracy of APEM and both models. This paper systematically examines the effects of stray capacitance and harmonics on the electro-thermal behavior of MOA. It is found that stray capacitance causes higher voltage on the top varistor block while also causing an overall increase in temperature and thermal non-uniformity. These effects are further significantly amplified in the presence of odd-order harmonics. The conclusions provide a theoretic reference for optimizing the durability and heat dissipation performance of MOA.