Source: Ding with Transformer and Reactor Magazine
Statistical analysis and prevention methods of transformer faults
Abstract: With the development of economic and technological development, the current demand for electrical energy in the world is increasing. Ensuring uninterrupted power supply for life, production, national defense, military, aerospace and communications has become a top priority in building production. In order to continuously supply high-quality electric energy to users, it is necessary to have strong technical support in all aspects of power generation, transmission, distribution and use of electricity. In this series of processes, the transformer always plays a very important role. Therefore, it is necessary to ensure that the fault of the transformer is as small as possible. Through the statistics and maintenance experience of transformer faults for more than ten years, the causes of transformer faults are discussed. Provides recommendations for the operation, maintenance, and inspection of the transformer. It involves: the maintenance method to extend its service life, the cause, type, frequency of the fault, etc.
Key words: transformer; fault statistics; analysis; prevention
Transformer failure not only damages the transformer that is running at the time, but also affects the normal operation of the power system, and even damages other equipment, causing serious accidents such as fire. Therefore, how to ensure the safe operation of the transformer has been widely concerned by countries all over the world. In the exhibition of power technology in modern and contemporary China, the safe operation of the power industry is a permanent and important theme.
This paper introduces the statistical conclusions of transformer faults, and provides reference for the construction of further smart grids in China and scientific statistical methods that can be used for reference to achieve the purpose of serving the power sector and serving the country.
First, the results of the failure statistics
Different departments have different transformers and different faults. In order to facilitate analysis, transformers can be divided into the following types: transformers for transformers in the cement and mining industries; transformers for the chemical, oil and gas industry; transformers for the power sector; transformers for the food processing industry; transformers for the medical industry; transformers for the manufacturing industry; transformers for the metallurgical industry; Transformers; transformers for commercial construction; transformers for the pulp and paper industry.
After long-term monitoring and statistics, it is known that the risk of transformer failure in the power sector is the highest when the frequency and degree are considered at the same time. The faults of the metallurgical industry transformers and the transformer faults of the manufacturing industry are listed in the second and third places respectively. According to the parameters given by the manufacturer, in general, the average operating time of various transformers under "ideal conditions" is 30 to 40 years. But this is not the case in practice.
The average life of a transformer with a fault occurring is 10 to 15 years, with the X axis representing the time and the Y axis representing the fault condition. Usually, the basin curve shows the initial life result, and the decreasing waveform curve shows the late aging curve. The significance of these curves is to determine the time and depth of periodic inspection and maintenance of the transformer during later use. It should be noted that the transformer in the power industry, his service life is related to the safety and normal use of equipment in many sectors.
After the reform and opening up, China has experienced a stage of rapid industrial development, and is still in the stage of transformation. This period has brought about the rapid development of basic industries, especially the large-scale expansion of the power industry. These power equipment installed from the 1970s to the 1990s have been designed and operated in accordance with the status of the aging replacement. The relevant authorities should pay special attention to the transformers that have been installed at these times.
Second, the cause analysis of transformer failure
After many years of research and years of experience, although the transformers are used in different types and aging trends, the basic causes of failures remain the same.
1, lightning strike
There are few studies on lightning strikes, because in many cases, direct lightning strikes will classify shock faults as “line inrushâ€. The best way to prevent lightning strikes is of course to install a lightning protection device that not only protects the transformer, but also reduces the inrush current in the power system and reduces transient fluctuations.
2, line inrush
Line inrush is a primary failure factor that should be included. Line inrush current (or line interference) includes: closing voltage, voltage peak superposition, line short circuit fault, flashover and oscillation, large current, voltage abnormality.
The most serious cause of such damage to the transformer is that the current and voltage are too large, so more attention must be paid to the adequacy of high current surge protection. Install an overcurrent protection monitoring device to perform real-time measurement and test reports on the transformer. And this result is sent to the overall system of the power system automation operation as an indicator of safe operation.
3, quality omissions
In general, the problems of the previous transformers in this area are not very large, only occasionally some are inevitable. For example, the wiring outlet end is loose or unsupported, the spacer is not tight, the welding is poor, the core insulation is not high, the resistance to large current is insufficient, and the oil in the fuel tank is not pure. Strengthen test testing and identify problems as early as possible when not installed.
4, insulation aging
In many transformer faults in the past, faults caused by insulation aging ranked second among all faults. Due to insulation aging, most transformers severely shortened service life, and the service life was about 20 years earlier. Develop a system to ensure that the rate of aging is up to the rated useful life.
5, overload
Due to overload, the transformer is operated at a rated power greater than the specified power for a long time. With the development of economy and technology, the power load is increasing, and the power plants and power departments continue to slowly increase the load. Directly causing more and more transformers to overload, the excessive temperature causes premature aging of the transformer's insulating paperboard, resulting in a decrease in the overall insulation strength. In this state, if there is a certain inrush current, the probability of failure will be high. Make sure that the load is under the rated operating conditions of the transformer, and do not operate for a long time with overload, which is not worth the loss. Careful careful monitoring of the top oil temperature is required in oil-cooled transformers. It is found that the high temperature is to be processed in time.
6, damp
Moisture is unavoidable. Due to various external natural causes, pipeline leakage, roof leakage, moisture intrusion into the fuel tank along the casing or fittings, and moisture in the insulating oil are often caused. The design and construction standards for the transformer should be matched to the installation location. If placed outdoors, make sure the transformer is suitable for outdoor operation. The dielectric strength of the transformer oil drops sharply as the moisture therein increases. One-tenth of the water in the oil can reduce its dielectric strength by nearly half. Oil samples from all transformers (except small distribution transformers) should be tested for breakdown frequently to ensure proper moisture detection and removal by filtration.
7, improper maintenance
As a result of the investigation, the probability of improper maintenance causing a transformer failure is ranked fourth in the probability of causing a transformer failure. This is mainly due to inadequate maintenance, uncontrolled or controlled installations, coolant leaks, dirt build-up and natural electrical and chemical corrosion.
8, damage and intentional damage
This type of external damage is thought to occur, often occurring at the end of the line directly connected to the user's transformer, but this damage is very uncommon.
9, the connection is loose
The possibility of such problems causing failures is also very small, and can be avoided to a large extent, but in practice, there are accidents in this area, and the research is different. This type of accident includes the manufacturing process and maintenance of the electrical connection. The most prominent problem is the improper cooperation between metals of different natures, but this situation is slowly decreasing. Another problem is the tightness between the bolted joints. It is not appropriate.
Third, the conclusion
With reference to the above statistical analysis results and some suggestions, an overall maintenance, inspection and test plan can be formulated in the future construction operation. This minimizes transformer failures and reduces the number of adverse effects from transformer failures. It also saves huge manpower, financial and material resources spent on troubleshooting, and the service life of the transformer will also increase.
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