## 5 Conclusions  
For regions with high loads and a high proportion of gas-fired units, the transmission loss of natural gas can affect the reliable power supply. To address this issue, a reliability-evaluation method for the power system considering natural gas supply fluctuations is proposed. Firstly, a reliability model of the natural gas supply chain based on the minimal cut set theory is constructed and the influence of policy regulations and economic market factors on system components is quantified. Secondly, a reliability-evaluation model for a power system that considers gas loss is constructed, and a non-sequential Monte Carlo simulation is used to solve it. Thirdly, a reliability-evaluation method considering the power system reserve capacity is proposed. Using the method to deal with the gas-electric system of a certain area, the main conclusions are summarized as follows:  
(1) The reliability of the natural gas supply is influenced by macro factors such as policy regulations and economic market fluctuations. The proactive promotion of low-carbon energy transformation policies will increase the proportion of natural gas, leading to further increases in the natural gas supply and demand while changes in the international situation, such as the Ukrainian crisis, have greatly altered the natural gas trade pattern. The same occurs for electricity prices, which have to some extent affected the natural gas supply. They can lead to a reduction in the gas supply from the source, thereby depriving the power system with a high proportion of gas-fired units of sufficient natural gas for power generation. (2) Coal-fired units can make up for the shortage of gas-fired units in areas with a high proportion of gas-fired units. In the case study, coal-fired units are connected at nodes 1, 7, and 8. From the results in Table 4, it can be seen that under different gas supply levels, there is no load shedding at nodes 1, 7, and 8, indicating that the coal-fired units are able to compensate for the insufficient output of gas-fired units, keep a balance of electric power at these nodes, and ensure the secure and reliable operation of the power system. (3) The reliability of the gas supply chain directly affects the reliability of the power system. When external macro factors such as policy regulation and economic fluctuations have an impact on the natural gas supply, assuming a proportional effect on all natural gas sources, as shown in Table 5, when the gas supply decreases from 18,000 m\({}^{3}\) to 7200 m\({}^{3}\), \(EDNS\) increases to 61.15 MW, \(SI\) increases to 0.24, \(ASAI\) decreases to 0.76, and \(AENS\) increases to 4.37. When the negative impact increases to the point where the gas supply drops to zero, \(EDNS\) reaches 69 MW, \(SI\) increases to 0.27, \(ASAI\) decreases to 0.73, and \(AENS\) increases to 4.93, indicating that the severity of system faults is extremely high and the availability of power supply in the electric power system also greatly decreases. (4) The reliability assessment of power systems considering the natural gas loss method proposed has a certain generality. As shown in Table 6, by using both Monte Carlo sampling (MCS) and Latin hypercube sampling (LHS) to simulate power system faults caused by fluctuations in the natural gas supply, the reliability-assessment results of the power system are similar. The \(EDNS\) obtained using the two methods are 57.19 MW and 57.48 MW, respectively, with only a slight difference of 0.52%. For the results of Average Energy Not Supplied (\(AENS\)), there is only a negligible difference of 0.47% between the results obtained by the two sampling methods. The results of the Severity Index (\(SI\)) and Average Service Availability Index (\(ASAI\)) are consistent, indicating that the model proposed in this paper has a certain degree of universality under different algorithmic solutions.