## 4 Simulation Analysis and Verification
### Simulation Results and Analysis
Under the same operating conditions, the higher the reliability level of the circuit breaker, the higher the probability of the circuit breaker being in a healthy state, the lower the probability of transferring to the fault state, and the state transfer rate between the service states is relatively low. In contrast, the lower the reliability level of the circuit breaker, the higher the probability of transferring to the fault state. This is also consistent with the phenomenon that better quality products are less likely to break down. Figure 9: State transfer probability diagram under different operating conditions. Through simulation analysis, it can be found that the reliability model of low-voltage circuit breaker overload protection based on the Markov process can simulate the change in its reliability during the service process, which can be used to formulate the maintenance strategy according to the actual service situation and provide a theoretical basis for improving the safe operation of the distribution grid system. Analysis of the Effect of Periodic Maintenance on the Reliability of Circuit Breaker Overload Protection  
Generally, the reliability of the power system is required to be 0.999 and above, i.e., the probability of the circuit breaker overload protection being in the normal state needs to be 0.999 or above. As shown in Figure 8, if overhaul is not taken into account, the circuit breakers with overload protection action times that do not meet the requirements will appear from the 29 th month onwards, so regular inspection is required to guarantee the reliability and security of the power supply. According to the state division method established in this paper, it is defined that the circuit breaker needs to be repaired when the safety margin is close to zero. Take class I products under good operating conditions as an example to analyze the probability of normal and faulty states at different inspection cycles, assuming that all the circuit breakers can be restored to the initial state after maintenance. It can be seen from Figure 8 that general faulty circuit breakers start to appear in the 29 th month and serious faulty circuit breakers start to appear in the 35 th month; therefore, it is chosen to carry out maintenance in the 28 th month. It can be seen from Figure 11a that in an inspection cycle of 28 months, the circuit breakers need to be repaired. In a cycle of 28, the probability for the normal operating condition of the circuit breaker can be maintained at 0.999 and above. Keeping the reliability level of the circuit breaker unchanged, a simulation of the minimum inspection cycles under different operating environments is carried out; the results are shown in Table 2.  
Figure 10: State transfer probability diagram for different circuit breaker reliability levels. As can be seen from the table, under the guarantee of the same power supply reliability, the operating environment of the circuit breaker will affect its failure rate; to improve the reliability and safety of the power supply in worse the operating environments, the maintenance cycle should be shortened. The current commonly used after-the-fact maintenance and planned maintenance strategies for circuit breakers have shortcomings such as high downtime losses and the tendency for over-maintenance.