0. Introduction Currently, there is considerable research on the reliability assessment of medium-voltage distribution networks and power generation and transmission combined systems. However, due to the complexity and large computational load, quantitative analytical research on the reliability assessment of high-voltage distribution networks is relatively scarce. This paper utilizes the advantages of Matlab simulation software in symbolic computation to quantitatively analyze and compare the reliability of three typical wiring methods of high-voltage distribution networks, obtaining analytical expressions for reliability indices of different loads and systems, which can be used as a reference for operation and planning personnel. 1. High-Voltage Distribution Network Reliability Assessment Algorithm 1.1 Probability and Frequency of Event Occurrence Let the failure rate and repair rate of a component be l and m, respectively. Then the unavailability rate (also known as ineffectiveness) and availability rate of the component are respectively: Assume that a high-voltage distribution network has K components, and the unavailability rate of each component is Pi (i=1,2,…,K). There are M components that fail in the system, and the remaining components are working normally. Let the m-th (1 2. Reliability Analysis and Comparison of Typical Wiring Methods 2.1 Three Typical Wiring Diagrams Based on the structural characteristics of the network and operational experience, three typical and common high-voltage distribution network wiring methods are summarized: double-T double tie, double-T double line, and Type II wiring method (see Figures 1-3). In the figures, the black box represents the tie switch, and C represents the i-th element. Figures 1 and 2 show T-connectors (A, C), and B and D are equivalent power supply points. The reliability difference between the two can be compared using the series-parallel reliability equivalence principle. Assume the failure rates of the circuit breaker, transformer, and line per unit length are l1, l2, and l3, respectively, and the repair times are r1, r2, and r3, respectively. Assume the distance between the high-voltage side of the transformer and the T-connector is d1, and the distance between the equivalent power supply point and the T-connector is d2, then the total line length d = d1 + d2; the tie line length is d3. 2.2 Reliability Analysis and Comparison of Typical Wiring Systems Due to the symmetrical wiring structure, only the reliability analysis results for loads L1 and L2 are given (the results for loads L3 and L4 can be obtained similarly). (1) Analytical expression of reliability index of load I Based on the probability and frequency of the event, the reliability index of load L1 in Figure 1 can be obtained. The probability of load L1 losing load is: The expected load of load L1 losing load is: The frequency of load L1 losing load is: (2) Wiring expression of reliability index of load L2 The probability of load L2 losing load is: The expected load of L2 losing load is: The frequency of load L2 losing load is Using the same analysis method, the node reliability index and system reliability index in Figure 2 and Figure 3 can be obtained. 2.3 Economic comparison based on equivalent annual value Assuming that the network planning year is n years, the discount rate is α, the present value is V, and the equivalent annual value is A, then V, A, α, and n have the following relationship: This formula can analyze and compare the economics of equipment investment, power outage losses, etc. 3. Case analysis In the above example system, d = 10 km, d3 = 5 km (d1 = 4 km, D2 = 6 km in Figure 2). The active power at each of the four load points is 10MW, and the line is allowed to transmit 30MW. The line fault rate is 0.0239 times/(km·a), with a repair time of 8 hours/fault; the circuit breaker fault rate is 0.05 times/a, with a repair time of 8 hours/fault; the transformer fault rate is 0.01 times/a, with a repair time of 24 hours/fault. Assuming a planning year of n=30 years, a discount rate of α=10%, an average output value of 10 yuan/kW, an investment of 150,000 yuan/km for erecting a 35 kV line, and operation and maintenance costs of 2%/year of equipment investment. Based on these data, the reliability indices of load points in three typical wiring configurations are as follows: For a double-T double-connected load, the failure probability of L1 is 4.28, the failure probability of L2 is 3.82, and the system failure probability is 10.90; for a double-T double-line load, the failure probability of L1 is 4.91, the failure probability of L2 is 4.91, and the system failure probability is 13.00; for a Type II load, the failure probability of L1 is 3.82, the failure probability of L2 is 3.82, and the system failure probability is 10.89. It can be seen that the reliability index of the Type II wiring configuration is superior to the other two. Using the equivalent annual economic analysis method, it can be seen that compared with the system in Figure 3, the system in Figure 1 requires an additional direct investment of 79,600 yuan per year, a corresponding increase in operating costs of 15,000 yuan/year, and a total investment increase of 94,600 yuan/year. Figure 2, affected by the T-connection, shows lower reliability levels at nodes and throughout the system. After comprehensive comparison, the Type II wiring configuration is the optimal solution. 4. Conclusion Reliability assessment algorithms were used to analyze three wiring methods: double-T double-tie, double-T double-line, and Type II. Analytical expressions for reliability indices under different structural loads and systems were obtained. Operators can easily calculate node and system reliability indices using these analytical expressions. Different wiring methods have a significant impact on node and system reliability. Based on a comprehensive analysis of economics and reliability, Type II wiring is recommended.