I. Introduction
The structure of modern power system is becoming more and more complex, the scale is gradually expanding, and the average electrical distance between various substations is getting smaller and smaller, making the risk assessment of power system more important. As the core part of power system, the main task of substation is to collect and distribute electric energy, which plays a decisive role in the smooth completion of the transmission task of system and the safe and stable operation of entire power grid [1]. Therefore, quantitative analysis of the risk of weak links in substations has always been the focus of research by experts and scholars. Traditional substation reliability assessment mainly uses two methods: analytical method and simulation method. The analytical method establishes a mathematical model through the parameters of the various components of the substation, and uses mathematical calculation methods to obtain various reliability indexs of substation. The main methods include the state space method [2]-[3] and the minimum cut-set method [4]-[6]. The simulation method generally refers to the Monte Carlo method [7]-[8]. In addition to analytical methods and simulation methods, other reliability analysis methods have emerged in recent years, such as hybrid methods [9], Bayesian network methods [10] and neural network methods. However, the current research generally only conducts risk assessment and weak link analysis for the main wiring in substation. The calculated indexs value is only the load loss index or capacity loss index in substation and regional power grid is not considered as an influencing factor in range. Therefore, the comprehensiveness and accuracy of evaluation results cannot be guaranteed. In view of the above-mentioned problems, the paper proposes an assessment method for the weak links of a substation based on the grid risk severity indexs. Firstly, the power grid risk severity indexs and load loss indexs are constructed. Secondly, the fault analysis of main wiring in the substation is carried out by analytic method, and then the evaluated substation is equivalently connected to the regional power grid for power flow and optimal dispatch calculation. Finally, the evaluation results of weak links of the substation taking into account the grid risk severity indexs are obtained. In order to verify the validity of the results, the IEEE-RTBS6 system is taken as an example for calculation and analysis. When analyzing the influence of the regional power grid on the weak link of the substation, the method described in this paper can be used to obtain a more conservative evaluation result, which provides a new idea for the evaluation of the weak link of the substation.