Reliability Evaluation And Weak Parts Identification Of Integrated Electricity-Gas System Considering Extreme Weather Effects

With the increasing environmental pollution caused by coal power generation,countries around the world are vying to seek the path of energy transformation.Natural gas has become the first choice for replacing coal due to its excellent properties such as cleanliness,low carbon emissions and high combustion efficiency.In this context,the gas-fired power generation industry in the world has continued to develop rapidly in recent years,and the installed capacity of natural gas power generation has been continuously increasing.The coupling relationship between the power system and the natural gas network has been strengthened,which cannot be ignored in the power system reliability evaluation.In addition,extreme weather events have occurred frequently in recent years.The component failures caused by extreme weather have been threatening the safe and reliable operation of power systems and natural gas networks.Supported by the National Natural Science Foundation of China(No.51677011),the main works of this paper focus on reliability evaluation and weak parts identification of integrated electricity-gas system.The optimal load flow model of the integrated electricity-gas system considering the coupling of gas-fired units is studied.A piecewise linearization method of gas pipeline flow equation based on feasible domain segmentation is proposed to reduce computational complexity.First,the DC power flow model is selected;a steady-state pipeline flow equation is established considering the node pressure and the pipeline flow constraint.Then,with the minimum operating cost as the objective function,a unified optimal load flow model of the integrated electricity-gas system is established.To solve the model,a piecewise linearization method based on the feasible domain segmentation is proposed,which can transform the nonlinear optimal load flow model into a mixed integer linear programming model.A simple integrated electricity-gas system consisting of a 6-node power system and a 7-node natural gas network,and a complex integrated electricity-gas system composed of IEEE RTS system and a 48-node natural gas network,are used to perform optimal load flow analysis.The results show that: Compared to the direct nonlinear modeling solution and the linearization method based on Taylor series expansion,the proposed piecewise linearization method can effectively improve the efficiency.In addition,the influence of the linear segment number on the accuracy and speed of the model is also analyzed.Considering the influence of extreme weather on the reliability parameters of transmission lines and gas pipelines,the reliability evaluation model of the integrated electricity-gas system is established.The weather conditions are divided into three categories: normal weather,extreme weather that only affects electrical components,and extreme weather that affects the components of the integrated electricity-gas system.Considering the probability of different weather types,the failure rate and repair rate of components in different weather conditions,the operating states of components in different weather conditions are sampled by the non-sequential Monte Carlo method.The optimal load curtailment model of the integrated electricity-gas system is constructed by modifying the optimal load flow model.In addition,based on the reliability index of power system,the loss of gas load probability and the expected gas load not supplied are proposed.The reliability evaluation of the integrated electricity-gas system composed of IEEE RTS system and 48-node natural gas network is carried out by using the nonsequential Monte Carlo simulation method.The results show that the reliability of the system is greatly reduced after considering the influence of extreme weather,and extreme weather have a greater impact on the reliability of transmission lines compared with the gas pipelines.The existing power system reliability tracing criteria were revised,and the weak parts identification method of integrated electricity-gas system based on reliability tracing was studied.Firstly,based on the proportional allocation criterion,considering the load curtailment difference before and after the failure of single component in the high-order fault event,the tracing criterion considering the load curtailment correction is proposed,and the reliability allocation of expected power shortage as well as expected gas shortage are derived.Based on the non-sequential Monte Carlo simulation method,the system reliability tracing is carried out.The reliability tracing is implemented on the integrated electricity-gas system composed of IEEE RTS system and 48-node natural gas network.The results show that the reliability index can be fairly and reasonably allocated to each system component.The weak parts of the integrated electricity-gas system can be identified.In addition,based on the results of weak parts identification,the reliability improvement measures were analyzed.