The thermal circuit model for dynamic overhead lines rating has the advantage of little dependence on ambient meteorology. But for the neglect of pulsating characteristics of thermal resistance

this model will lead to large errors in risk assessment for dynamic rating when the conductor temperature fluctuates. This paper proposes a new thermal circuit model for dynamic overhead lines rating which considers pulsating characteristics of parameters by introducing the parameters of average thermal resistance and pulsating thermal resistance. The model parameters and their stochastic characteristics are determined by parameter identification and Markov chain method. A temperature rise experiment platform for current-carrying conductor is used for model verification. The experiment and calculation results show that the precision of average thermal resistance determined by parameter identification is higher than that determined by the traditional method if the conductor temperature fluctuates. The statistical law of pulsating thermal resistance can be obtained and a simulated sequence which has a similar statistical law can be generated by Markov chain. After that

the proposed model can reflect conductor temperature fluctuation caused by ambient meteorology and estimate ampacity in the form of probability. Using this model

the risk of dynamic overhead lines rating is controlled in a rational range and the basis for power system operation and scheduling is proved.