Power Transformer Status Monitoring And Analyzing System Based On DGA

1. IntroductionThe power transformer is not only the key device in a power system, but also one of the most accident-prone equipments in an electric system .Techniques for on-line monitoring of power transformer play an important role in keeping the reliability and stability of the electricity supply. In a certain extent, the component and content of dissolved gases in the transformer indicate the insulation aging and malfunction degree of the transformer. Dissolved Gas Analysis (DGA) is one of the main methods to diagnose the internal malfunction in the transformer. The results reflect the potential malfunction in a transformer more sensitively.The efficiency is higher than 85%. And it is easier to achieve by on-line monitoring. DGA has been recognized as the most effective way to monitor and diagnose the early malfunction of oil-filled power transformers, and prevent catastrophic accidents. Therefore, by the way of detecting the Dissolved Gas in transformer oil on-line, we achieve the diagnosis and prediction of the potential malfunction in a working transformer, which is the start point of the paper.2. Research ContentThe aim of this paper is to design the power transformer status monitoring and malfunction analyzing system based on DGA. By the way of analyzing the chromatogram of the dissolved gas in the oil, we achive the real-time monitoring of the content of the 5 characteristic gas in the oil on-line, in order to diagnose and analyze the working status of the power transformer. The system achieve the data collecting, data communication, spectrum processing, quantitative analyzing, and malfunction diagnosing under the control of computer. The detailed courses are as follows: The carrier gas carries the measured gas to inpour in the chromatography and Flame Ionization Detector (FID). The system transforms each of the concentration into analog signal pro direct ratio to concentration. After AD conversion, the signal is transmitted into computer by wireless transmission. The working station is able to achieve spectrum processing, quantitative analyzing, and realize the malfunction type diagnosing by using Grey Relation Malfunction Diagnostic Algorithm.(1) The Relation Research between Malfunction Type and the Dissolved Gas.Generally speaking, insulation material decomposes different gases for the different malfunction. Because of different degree, the amount of generated gas is different for the same malfunction. According to the gas component and content dissolved in the oil, we can judge the character and degree of malfunction. The paper analyzes the common malfunction diagnosing methods such as character gas method, three-ratio method etc.(2) The Research of the Grey Relation Malfunction Diagnostic Algorithm which takes DGA as the Eigenvector. Inorder to improve the malfunction diagnosing methods based on chromatography analysis existing, we lucubrate the grey relation malfunction diagnostic algorithm which takes DGA as the eigenvector, and establish the 5 Characteristic Gas in the oil as the eigenvector. We build the grey relative analyzing model, and prove that it is effective to predict the developing trends of the malfunction of the transformer by using this method. The method has many advantages,such as clear concept, exact diagnosing, simple calculating.(3) The Design and Realization of the Characteristic Gas Signal Detecting Circuit. The system chooses hydrogen flame ion detector (FID) as detector from the chromatographic column chromatography four characteristic gas(CH4,C2H2,C2H4,C2H6) component concentration signal detections, and select the low input bias current operation amplifier AD549 as signal amplifier. Because the system adopts hydrogen as carrier gas and single FID as detector, we design the separate hydrogen gas density detection circuit. We choose the H2/M-1000 hydrogen gas density sensor, which produced by Switzerland corporation MEMBRAPOR. It's distinguishability reaches 1ppm, meet the require of hydrogen gas density detention sensitivity. The test result indicates that the characteristic gas detection circuit has the high precision , and the maximal relative error isn't more than 3.5%,which meet the requirement of the analysis and judge guide rule of transformer oil dissolved gas.(4) The Design and Realization of the Temperature Control circuit. The temperature directly influences the selected separating effect of chromate graphic column,the stability of baseline and the sensitivity of detector. The system adopts controller 6100PLUS PID produced by WEST corporation, which realized the temperature control to chromategraphic column,ion chamber and transition oven. According to the actual condition, though MCU and PID controller's serial communication to set value. PID controller real-time detects the current temperature, and compares the temperature value with set value, and calculates the discrepance and controlled variable, which is transformed by D/A, then output toactuator .By control the SSR on-off to realize heat or thermolysis , and make the temperature constancy at set value. The temperature stabilization accuracy reaches±0.1℃.(5) The Design and Realization of the Data Transmission circuit. The data information detected by system will be transformed to computer ,and analysis processing by chromatogram workstation. The system adopts distance wireless communication module to realize the data communication from the remote terminal unit and the main control equipment. The module uses the high-powered microprocessor as a core, and adopts high efficiency FFC forward error correction technology combined with high-powered wireless radio frequency IC, which has strong noninterference and reliable data transmission. The system main MCU links with the module SRWF-508 by MAX232, main control computer directly links with another module SRWF-508. The data between the two wireless modules transparent transmission, equal to the wired serial port connection. The wireless transmission speed rate proportional to interface baud rate, meet the requirement of system real-time monitor.(6) The Design and Realization of the Chromatography Data working station. We establish the holistic design blue print of the Chromatography Data working station. And we make the function design by Delphi language. So the working station is able to achieve the data collecting, data communication, spectrum processing, quantitative analyzing, and realize the malfunction type diagnosing by using Grey Relation Malfunction Diagnostic Algorithm.3. ConclusionThe paper emphasis studies the grey relevant failure diagnosis algorithm using DGA as characteristic quantity. The soft hardware realize the characteristic gas component signal and multiplex status signal's collection, display, control and wireless remote transmission. The computer workstation realizes the quantitative analysis for five characteristic gas and the failure diagnosis for transformer status. The test result for reference sample is quite approximated to actual value , the error is less than 3.5%, which meets the requirement of engineering examination. The system diagnoses report for type malfunction's gas component content in reasonable agreement with the transformer's true malfunction, which proves the system has the whole working reliability.