Paper Keywords: electrical equipment condition maintenance strategy

Abstract: At present, there are serious defects in the regular maintenance system of electrical equipment in power system, such as insufficient maintenance, excessive maintenance or blind maintenance. This paper studies how to arrange the maintenance of electrical equipment reasonably, save the maintenance cost and ensure the high reliability of the system.

1. Traditional scheduled maintenance system

Regular maintenance of equipment is the basic equipment management method adopted by the majority of electric power enterprises for many years. Its biggest feature is to make plans and arrange equipment maintenance on the basis of simple time period and according to the requirements of laws, regulations and systems. This maintenance method, regardless of the actual condition of the equipment, as long as? Due? Just? Compulsory? . This method does not consider the objective state difference of equipment, which leads to a series of problems such as excessive maintenance, waste of resources and influence on the reliability of equipment operation.

1. 1 electrical equipment? Healthy? There are differences in conditions

Electrical equipment? Healthy? First, the innate conditions of equipment are different, and the technical conditions of imported equipment and domestic equipment are different; The same domestic equipment, different manufacturers have different product quality because of different technology and management levels; Even the same manufacturer, due to the progress of technology and management, the quality of products in different periods and batches will be different. Therefore, it should be admitted that the initial state of equipment put into operation is very different. Secondly, the use environment of the equipment is different, and different environments will have different effects on the operation of the equipment. There are mainly two kinds of environments: first, the external natural environment in which the equipment is located is different, especially the power supply equipment, most of which are exposed to the outdoor natural environment, and the influence on the equipment is quite different due to factors such as temperature, humidity, pollution, ultraviolet rays and sunlight; Secondly, due to the different positions of equipment in the power system, the operating voltage, short-circuit current and thermal stability time of the system are also different, especially the short-circuit capacity when the system fails. In addition, the use of new technologies and new materials has greatly improved the technical level and conditions of the equipment. Especially after the 1990s, many foreign advanced technologies, equipment and management have been introduced into China's power equipment manufacturing, and the equipment has been updated quickly, and the overall technical level has been greatly improved, so the equipment level of the power system has been greatly improved.

1.2 Problems existing in the regular maintenance system

Because the initial state of electrical equipment is very different from the running state of field equipment, that is, the field equipment's? Healthy? Conditions vary widely, and the regular maintenance system almost ignores these differences, and adopts a unified and one-size-fits-all regular maintenance method, which is mainly manifested in the maintenance results, either excessive maintenance or insufficient maintenance. The actual situation of the project is mostly over-maintenance, which often happens? Cure a minor illness? 、? Disease-free treatment? The phenomenon of blind maintenance, the result of this excessive maintenance, will have the following disadvantages of maintenance:

(1) Some equipment in good condition has faults or potential faults due to blind maintenance. Maintenance can not restore the original reliability of the equipment, but increase the hidden dangers and failure rate of the equipment.

(2) The availability of equipment is reduced, and repeated maintenance forces the equipment to stop. Interrupting uninterrupted power supply to users is the inevitable result of increasing the number of downtime and maintenance. Improving the reliability of power supply is a very important basic assessment index for power supply enterprises. At present, regular maintenance is the main reason for the outage of electrical equipment, which often accounts for more than 60% of the total outage time.

(3) increase the cost of equipment operation and management, so that enterprises are at a loss in the market and development competition. Electrical equipment maintenance cost is the main cost in enterprise management, which occupies a large proportion in the economic activities of electric power enterprises and directly affects the economic benefits of enterprises. Therefore, in order to improve the economic benefits of enterprises, it is necessary to reform the current regular maintenance system of enterprise equipment, and guide the analysis and selection of maintenance strategies with the viewpoint and requirements of economic benefits.

Secondly, the status and influence of each device in the power system are different, and the components in each device have different effects on the function of the device. Is it possible or necessary to carry out condition monitoring, fault diagnosis and condition maintenance for all equipment? That is, can condition-based maintenance completely replace regular maintenance? In fact, it is technically difficult to monitor and diagnose the condition of all equipment and its components, and the cost of monitoring all equipment and its components is unbearable. Therefore, it is impossible for future condition-based maintenance to completely replace regular maintenance, but condition-based maintenance and regular maintenance coexist.

2. Selection of condition monitoring characteristic quantity in condition maintenance.

With the development of sensor technology, there are more and more monitorable states of electrical equipment. The main condition monitoring features of several important electrical equipment are as follows:

(1) transformers: mainly oil-immersed power transformers, followed by SF6 gas insulated transformers and epoxy resin cast insulated transformers. The main monitoring features include: dissolved gas (single or multiple) content in oil, partial discharge, winding deformation, core grounding current, dielectric loss of high-voltage bushing, micro-water content in oil, etc.

(2) Capacitive equipment: including current transformers, capacitive voltage transformers, capacitors, cables, etc. The main monitoring characteristics are: dielectric loss, leakage current, equivalent capacitance (partial discharge can also be monitored) and so on.

(3) Zinc oxide arrester: mainly monitors resistive current and partially monitors total leakage current.

(4) High voltage circuit breakers: including oil circuit breakers, SF6 circuit breakers (including those in GIS) and vacuum circuit breakers.

At present, the characteristics that can be monitored include: coil current, stroke, speed of closing and opening lines, mechanical vibration of operating mechanism, dynamic loop resistance, etc. A certain state of electrical equipment is often reflected by several state features, and one state feature may come from multiple states of the equipment, so the selection and extraction of state features is one of the difficulties in state evaluation. When identifying the fault state and normal state of electrical equipment in operation, it is often misdiagnosed or missed because of improper selection of state characteristics. The main reason for misdiagnosis is that the characteristic parameters of normal state and fault state overlap, that is, the state characteristics are fuzzy. Therefore, it is necessary to select representative and effective state characteristic parameters.

Therefore, it is necessary to further process the condition monitoring signals collected by sensors, with the purpose of suppressing interference, extracting signal characteristics, putting forward useful information in complex signals, extracting the characteristic information of equipment in operation, and improving the sensitivity of equipment diagnosis.

3. Condition evaluation and maintenance decision of electrical equipment based on variable weight synthesis.

There are many methods of electrical equipment condition evaluation, which are mainly divided into traditional weighted scoring method and emerging artificial intelligence evaluation method.

Weighted scoring method scores the factors that affect the equipment state in the pre-selected factor set, and then carries out weighted synthesis on each score to obtain the evaluation result of the equipment state. These factors can include pre-test, online monitoring, family quality defects and equipment quality. It can also focus on the narrow sense of equipment state monitoring and extract the component sets of various characteristic parameters reflecting the equipment state. The scoring method can be expert scoring, empirical formula and mathematical function fitting calculation. According to the actual needs, the scoring results can be further blurred and fuzzy comprehensive evaluation can be carried out.

The artificial intelligence evaluation method is represented by neural network, and usually takes the characteristic parameters obtained from condition monitoring to reflect the state of equipment as the evaluation elements. Neural network regards the relationship between the state and the state characteristic parameters of electrical equipment as a nonlinear mapping relationship, with the state characteristic parameters of the equipment as the network input and the state of the equipment as the network output, and establishes this complex mapping relationship through the learning process of samples. Neural network evaluation method needs a lot of training data for training, and is usually used for qualitative evaluation. The key of equipment condition evaluation lies in: (1) the determination of evaluation factors, that is, the determination of the set of factors that can correctly reflect the equipment condition, such as pre-test, condition monitoring, ethnic defects, etc. ; (2) Selection of evaluation methods, including expert scoring, mathematical empirical formula, artificial neural network, etc. (3) The method of comprehensive evaluation and the determination of evaluation results usually adopt hierarchical weighted comprehensive evaluation.

References:

Tian Ling, Xing Jianguo. Discussion on the decision-making method of condition-based maintenance of electrical equipment [J]. Power Grid Technology, 2004,28 (16).

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