Research On Maintenance Decision Method For Substation Main Equipment Based On Reliability Theory

Substation is the hub of power system. In the long run, the substation equipment especially power transformers and circuit breakers is affected by itself and external factors, and its reliability decreases with time. Therefore, the maintenance work is one of the relatively daily works of the power supply enterprises. Power supply enterprises gradually carry out the condition-based maintenance for substation equipment. However, it seems that condition-based maintenance for all substation equipment is too expensive, and condition-based maintenance is still insufficient. In addition, the ultimate aim of maintenance is to reduce the power grid risk, so the reliability-based maintenance decision should consider not only substation equipment itself, but also the reliability of the power grid. In the whole process of substation equipment maintenance management, using equipment reliability theory and power grid reliability evaluation method to make maintenance decision is more scientific and can improve the level of maintenance management. In order to solve those problems, this paper uses equipment reliability theory with power grid reliability evaluation method to study the maintenance decision method for power transformer, circuit breaker as well as their components. The main contents of this paper are as follows:a) Considering that a large number of main equipment of substation has not been applied for the condition-based maintenance, lots of statistical data is needed to analyze the reliability of main equipment of substation to determine whether the equipment needs maintenance or not. Aiming at main equipment of substation that has not been applied for condition maintenance, a reliability evaluation method for main equipment of substation is proposed based on a lot of historical data. This method considers the dynamic randomness of maintenance process which quantifies the effect of maintenance, and an average time between failures model is established. Using the average time between failures as the maintenance optimization time window, a rolling window method of maintenance cycle optimization model is built based on minimization of the sum of maintenance cost and outage cost. Preventive maintenance is only a partial maintenance or targeted on maintaining some important parts, which is non-uniformity maintenance. A decision-making method is proposed to clarify the components maintenance level for main equipment of substation in preventive maintenance. First of all, this method analyzes the failure modes of components, and quantitatively describes the effect on the overall performance substation equipment by different failure modes, then it takes component failure frequency into account, and calculates the degree of importance. Finally, a maintenance level decision graph is proposed to determine the maintenance level of substation main equipment components.b) Aiming at main equipment of substation that has been applied for condition maintenance, the key is how to use condition monitoring data effectively to judge the currently running state of substation main equipment. Using online monitoring data, a reliability status assessment method of transformers and circuit breakers based on Gaussian kernel density function is proposed. This method uses the gas content and its absolute production rate in transformer oil, breaker closing coil current waveform critical point in time as the condition monitoring quantity, and calculates the abnormal index of transformer and circuit breaker. To avoid the effects by the adverse data of condition monitoring, this paper calculates the probability of abnormal for main equipment of substation using the current and adjacent continuous monitoring dates to improve the accuracy of reliability condition evaluation.c) Power grid often encounters a kind of situation that multiply main equipment of substation requires maintenance at the same time, and the main equipment of substation at the different locations of the power system has different effects on the reliability of power grid. If the equipment seriously affects the system reliability when it continues running, this equipment should give priority to maintenance, on the contrary, it can be maintained later. In this way, power supply enterprises can reasonably use the limited maintenance resources and the maintenance work can have a minimal effect on reliability of the power grid. Based on this, a maintenance order decision method is proposed for main equipment of substation considering potential operating risk. This method analyzes the system risk when the main equipment of substation exits directly and continues running, and then calculates the maintenance urgent degree of main equipment of substation to arrange the maintenance order that can reduce the power grid risk caused by the maintenance.