Monitoring method for partial discharge of power transformer
Published time: 2019-09-09
Research data shows that when the number of large-scale electrical equipment increases exponentially, the power transmission load of the line will increase, and the voltage level is too high, which will cause certain impact damage to the safety of the power grid. In the entire power grid system, the power transformer acts as a node, which plays an important role in reducing the voltage to the household.
First, partial discharge detection
Through the partial discharge test, the safety of the internal insulation structure of the transformer can be accurately measured, which is the most widely used detection method by transformer manufacturers. Due to the scattered electric field distribution in the working process of the transformer and the complicated structure of the transformer, it is easy to infiltrate the air and impurities between the inner insulating material layers during operation and use, and accumulate in the long-term after the charge. Under the action, it will lead to partial discharge. At present, the existing data analysis shows that the causes of partial discharge phenomena are roughly divided into two types: electric field type discharge and current type discharge.
The main hazard of partial discharge is that it can damage the insulation material of the power transformer from the structural form, which further leads to the loss or complete absence of the insulation of the protective material. When the partial discharge occurs in a wide range and there is no corresponding external protection measure, the breakdown of the insulating material occurs, causing damage to the transformer. The role of partial discharge monitoring is mainly to test the maximum load of the internal insulation structure by destructive testing of the transformer. Within the effective range of the safety standard, a test voltage that meets the technical requirements and safety indicators is applied to achieve partial discharge of the power transformer. Technical diagnosis.
Second, the partial discharge monitoring method
(1) Electrical measurement of partial discharge
The power monitoring of partial discharge of power transformer mainly includes monitoring of internal charge distribution, tracking and monitoring of electrical signals, and monitoring of insulation performance of insulating materials. Common monitoring methods include high frequency instrument monitoring method, alternating current and voltage conversion method, and ultra-wideband measurement. Frequency method.
First, UHF partial discharge monitoring
Ultra-high frequency partial discharge monitoring is mainly based on the powerful data analysis capability of the computer. By inputting and outputting the difference between the charge at both ends of the transformer, the effective tracking of the lost charge can be performed, so that the damaged part of the insulating layer can be visually seen. Timely maintenance of technicians. The disadvantage of this method is that due to the complexity of the internal structure of the power transformer and the collision in the charge flow, it will bring certain errors to the measurement and data acquisition of the computer.
Second, overclocking broadband partial discharge monitoring
The overclocking broadband partial discharge monitoring method is suitable for partial discharge detection of industrial large transformers. With the high-frequency scanning and small probability misalignment, it is possible to simultaneously monitor the transformer insulation layer in a large range at the same time. Because of the advantages of wide monitoring range, full coverage, and large amount of information collected, this method is widely used for partial discharge monitoring of transformers in large-scale operation equipment.
(2) Non-electrical measurement of partial discharge
The non-electrical measurement of partial discharge should initially be detected and tracked in biological and chemical aspects, mainly in the body. Due to the development of modern science and technology, each discipline can achieve good mutual communication, especially between disciplines with relevant research content, and each other's professional measurement methods can be very common. This method uses chemical quantitative analysis to analyze the chemical cycle by measuring the chemical properties of the ions in the transformer to determine the chemically active regions. Similar to the non-electrical measurement method, there are transformer oil chromatography online monitoring method, transformer oil hydrogen concentration online monitoring, collectively referred to as the three chemical methods of transformer partial discharge monitoring.
(3) Optical fiber technology detection method for partial discharge
Fiber optic technology is a relatively successful ultrasonic detection method. The fiber optic technology is linked to the local detection of the power transformer, and the technological innovation of the local detection of the transformer is realized. The use of optical fiber to detect partial discharge has obvious advantages: the optical fiber propagates unidirectionally in the internal path of the transformer, thereby avoiding the repeatability of the partial discharge signal and preventing the secondary influence on the composite circuit. The measuring principle is that when the insulating layer of the power transformer is broken down, the ultrasonic signal emitted from the discharge portion will propagate along the path of the optical fiber, and no collision of the charge volume occurs in the process, thereby avoiding the extra loss of the electric charge. When the charge propagates to a certain extent, the external modem connected to the computer extracts the electrical signal generated by the partial discharge and converts the data into a computer connected to it, and then performs a high-speed quantitative relationship calculation through the computer.
(4) Infrared detection method for partial discharge
Infrared detection is also applied to the detection of partial discharge of power transformers. Infrared detection is based on the temperature rise of the partial discharge point, and the hot spot measurement is realized by the thermal imaging principle of the infrared detector. However, due to the complexity of the transformer structure and heat transfer process, it is very difficult to directly detect the partial discharge located inside the transformer body by using the infrared imaging method. At present, infrared detection of transformers is effective for external faults of the transformer (including poor connection of conductors, eddy currents caused by magnetic flux leakage, failure of cooling devices, and failure of transformer bushings).
Third, electromagnetic interference and suppression of partial discharge detection
The partial discharge detection of the transformer can directly and effectively reflect the actual insulation of the transformer. However, in actual measurement, the measurement result is reduced to a large extent due to external environmental factors. In severe cases, even the measurement work cannot be performed. keep going.
The factors that cause partial discharge detection to not proceed normally are diverse and can be divided into different categories according to different classification conditions. Common interferences include periodic interference, pulse-type interference, white noise interference, and laboratory shielding interference. Strongly targeted suppression measures are adopted for different types of interference. As far as the current interference suppression situation is concerned, a completely effective control method has not been found. The existing measures are more or less restricted by some unfavorable factors, and the application scope is narrow. According to relevant professional reports, the more advanced digital anti-interference processing system is being established. With the help of modern science and technology, it has made good progress. I hope that with the continuous development of relevant scientific research work, we can develop a specific target in the future. A new type of transformer partial discharge anti-interference system with strong and wide application range.
The ultimate goal of partial discharge detection is to achieve better protection of the safety performance of power transformers. With the continuous improvement of computer technology and digital signal processing technology in the power industry, partial discharge detection can provide sufficient performance improvement and replacement for power transformers. The data guarantee will be more widely used in the future.
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