毕业设计英文翻译使用电超声波技术检测变压器局部放电1.doc

译 文原文题目：Transformer Partial Discharg Detection Using Electrical-Ultrasonic Technology 译文题目: 使用电超声波技术 检测变压器局部放电 学 院: 电子信息学院 专业班级: 电气工程及其自动化2009级7班 学生姓名: 李龙龙 学 号: 20903040702 Transformer Partial Discharge Detection UsingElectrical-Ultrasonic TechnologyWei Jiang, Fan Liu, Zhiyuan WangSichuan Electric Power Research InstituteChengdu, ChinaAbstractPartial discharge (PD) is usually happened caused by flaw and deterioration of transformer insulation. It is the main reason of the accident of transformer and power system. Therefore, it's necessary and important to detect the partial discharge of transformer while operating and manufacturing. When PD of transformer internal insulation occurs, electromagnetic waves, sound waves and other signals are produced. According to supersonic signal, we can detect the location of PD. But this method can not test the number of charge. With electrical-ultrasonic detection method, it is easy to locate PD and test the number of charge. In this paper, a method of electrical-ultrasonic detection is presented, which is based three-dimensional scatter point and ultrasonic hit to time. The method is effective to locate fault of transformer insulation. To validate the approach, a case is introduced.KeywordsPartial discharge; Electrical-supersonic detection method; Pulse current method; Power transformer. INTRODUCTIONPartial discharge is common on account of flaw and deterioration of insulation, especially in power transformer, and is the main reason of the accident of transformer and power system. Therefore, it's necessary and important to detect the partial discharge of transformer while operating and manufacturing. When PD of transformer internal insulation happen, electromagnetic waves, sound waves and other signals are produced at the same time. Though detect the ultrasonic signal, we can locate the PD1-3. PD detection using ultrasonic signal can locate the discharge, but this method can not test the number of the discharge. Partial discharge test can effectively test the discharge, but can not accurate locate 4-6. If we use PD ultrasonic location and partial discharge test at the same time, the number and location of discharge can be tested. We call this method is electical-ultrasonic technology 7-10. A method of electical-ultrasonic detection is presented in this paper, which is based three-dimensional scatter point and supersonic hit to time. With a case, the accuracy of PD electical-ultrasonic detection method is demonstrated. TRANSFORMER PD ELECTICAL-ULTRASONIC DETECTION PRINCIPLEWhen partial discharge of transformer internal isolation occurs, the ultrasonic signal will form spherical wave and spread to the surrounding with 1400m / s speed in the transformer oil. As long as placed ultrasonic sensors on the outside of transformer tank wall, ultrasound produced by PD can receive. We can locate the discharge of by detecting ultrasonic signal. But it hard to test the number of the discharge only by ultrasonic signal. Partial discharge test based on pulse current method can not accurate locate discharge source, though it can effectively test the discharge. So, electrical-ultrasonic, that detect both ultrasonic signal and pulse current discharge, can realize to test the number and location of discharge. The detection principle in Figure 1.Fig.1 Transformer PD electical-ultrasonic detection principleA. Partial Discharge Ultrasonic LocationPD ultrasound location method is that placing ultrasonic sensors on a few points of the transformer tank shell, composed of acoustic array to measure the spread time or relative time of each sensor, then according to the time to solve equations of PD source location.Fig.2 Transformer PD ultrasonic detection principleWe can see from Fig.2. Set the coordinate of discharge source location is P（x,y,z）, the transformer length, width and height are m, n and h. there are six sensors on the transformer tank shell. Their coordinates are （0,）, （,n,）, （,0,）, （m,）, （,0）, （,0）. So, the straight-line distance from the six sensors to PD source are:（1）（2）（3）（4）（5）（6）Set， are the time difference between PD source to 、 and PD source to. Set v is the ultrasonic speed. Therefore（7）（8）（9）（10）（11）We can determine the locations of，.when we set the sensors on transformer tank shell. The time difference of can be between ，and can be measure by Multi-channel oscilloscope. So, the location of PD source can be get by solve formula（1）（11）. Because transformer internal structure is complex, which is compound of different materials, such as oil, copper, silicon steel and so on. Ultrasound propagation path is not complete linear, but it is include some refraction. Because the frequency of ultrasound is very high, refraction is very small. Therefore, by ultrasound signal, we can accurately detect the location of partial discharge. More sensors we use, more accurate location we get.B. Transformer Partical Didcharge Test(1) Test methodPartial discharge test using power supply of five times the frequency,250Hz, apply test voltage in the transformer lowvoltage winding. A detection impedance are connected to the final layer of tested casing insulating paper, then link to the PD test apparatus by data cable.To supplement the transformer capacitive current, some reactors are paralleled to the transformer low voltage side, where is applied test voltage. Before the test, a square wave, with 500pC charge, are injected into the high (medium) voltage final layer of tested casing insulating paper to calibrated the number of discharge. Setting PD test apparatus to adjust PD 100 meter gauge shows full-scale grid, which indicated 500pC discharge. Transformer PD test principle using pulse current method is shown in Fig 3.Fig.3 Transformer PD test principle using pulse current method(2) Test voltageSet is the maximum operating voltage, is equal to and is equal to . Turn on power supply in less than . Up voltage to , maintained this voltage for 5 min, maintained it for 5 min, and voltage to to and maintained 24 min. Then down voltage to , maintained it at less for half hours and test the number of transformer PD. Further reduced this voltage to , and maintained it for 5min.Turn off power supply when it less than . In the entire period of test, partial discharge should be monitored.(3) Test compensationTaking into account that the capacity of the frequency power supply unit and possible resonance, discharge-free reactors are used in the test to compensate capacitive current. According to the actual power capacity, the required reactive power compensation can be estimated by the following formula:（12）Using the reactors to compensate for capacitive currents. During the voltage up to 20% and 50% , monitor compensation reactor and transformer current, and determine to increase or decrease the capacity of compensation reactor. EXAMPLE OF ELECTICAL-ULTRASONIC PD DETECTIONAcetylene in oil of a 220kV substation #1 power transformer is excessive. Follow-up examination found that acetylene is still excessive, and there is a trend to further increase. Inner insulation of the transformer is likely to exist the phenomenon of partial discharge. To prevent transformer failure，the Power companion stop the transformer, evaluate its insulating state by the method of electical-ultrasonic detection and detect possible partial discharge location.A. Ultrasonic Partial Discharge Field TestingDuring partial discharge test, ultrasonic PD field testing is carry out with DISP 24-channel ultrasound PD detection system.(1) Transformer modeling and sensor placementSetting the origin of coordinates is the bottom right corner along the tank of transformer high voltage side. We can see from Fig.4. X-axis positive direction along the tank wall, the phase C direction toward the phase B. Y-axis direction is up and perpendicular to the tank bottom. Z axis is perpendicular to the tank wall from outside to inside. The length of tested transformer is 8.86m, its width is 2.75m and its high is 3.56m. Set up the transformer geometric model as X = 8.86m, Y =3.56m and Z = 2.75m.Fig.4 Transformer PD location coordinatesthe sensor R15I is used that have 18 channels, built-in ultrasonic pulse 40 db and preamplifier resonant frequency 150kHz. There are six sensors placed on the positive and negative surface of the transformer, four sensors placed on the two sides transformer, and two sensors placed on the transformer bottom. after finishing sensor placement, the threedimensional model of the transformer is shown in Figure 5.Fig.5 The three-dimensional model of the transformer with sensors(2) Parameter settingparameters setting of ultrasonic detection for transformer insulation fault are threshold value, sound speed, sample rate, filter range and so on. Set the amplitude of ultrasonic signal is 45dB, and the float threshold value is 4dB. As magnetic noise energy of transformer core concentrated in the 1065kHz frequency range and transformer noise is focused on below 15kHz frequency band, the strongest frequency band in the vicinity of 1.5kHz. The filter frequency analog filters lower limit is set to 1kHz, upper limit is 400kHz, and sampling rate is 1MSPS. Set the velocity of ultrasonic signal is 1400m/s, the minimum impact is 4 and maximum impact is 8.According to desired output, we can set hit to time, energy to time, amplitude to time, and three-dimensional scatter plot, etc. This test use multi-channel to show the plot of hit to time which facilitated analysis and comparison to locate the transformer insulation fault.(3) Result of PD detectionIt took 6 hours to locate the transformer insulation fault. There are obvious sudden and high amplitude acoustic emission signal during the testing. The distribution of ultrasonic signal amplitude is a large range, and the most amplitude is 2810dB. signals triggered frequently. Some channels can always capture the signal. Ch1, Ch2, Ch7, Ch8, Ch13, Ch14 signal have PD characteristics. These six-channel signal meet the ultrasonic signal characteristics. the ultrasonic signal amplitudes of Ch7 and Ch14 are greater, respectively 1892dB and 2810dB. Therefore, we think that these six channels may be received partial discharge signal and the corresponding discharge points concentrated in the near block comic high of transformer phase A.Fig.7 Scatter plot of transformer insulation fault locationFigure.7 shows that: discharge points focus on the channel 1,2,7,8,13,14 which is in accord with the results of the sensor receiving. So, if there is partial discharge of transformer insulation, it should concentrate in the vicinity of comic high seat of transformer phase A. The number of partial discharge can be tested by partial discharge test carried out at the same time.B. Transformer Partial Discharge TestingWhen we have transformer insulation ultrasonic detect, carry out partial discharge testing at the same time to test the number of partial discharge. Transformer main parameters: Type: SFPSZ7-120000/220Rated voltage:（220±8×1.25%）/121/10.5 kVRated capacity: 120/120/60MVAConnection: d11(1) Test voltage calculationHV winding: Power system maximum operating voltage: =252 kVTest voltage: =218 kVMV vinding: Power system maximum operating voltage: =126 kVTest voltage: =109 kVHV winding: =139.4 kVMV vinding: =69.8 kVTest voltage times: K=1.56The test voltage of LV winding:=60.06 kVThe test voltage of MV winding:=（）×1.56=108.9 kV(2) Compensation estimatesConsider the capacity of doubling frequency power and possible resonance, no-discharge reactor is use to compensate reactive power during the test. The capacitance is 16000pF to estimate the capacity compensating for the reactive power.Using the reactor to compensate. When the voltage is 20% and 50% of the , we monitor the currents of the compensating reactor and transformer. According to the size of these two currents to increase or decrease the compensation reactor capacity.(3) Results of partial discharge testPartial discharge test of transformer phase A show that: when test voltage increased to 116kV (about ), the partial discharge reached 618pC and exceeded 500pC that is the amount of partial discharge limits provided by GB50150-2006 "installation of electrical installations-electrical equipment transfer testing standard".Fig.8 The number of partial discharge at The number of partial discharge reached 5010pC, when test voltage increased to . Discharge pulses were in the first and third quadrant and they were symmetric, which is the typical PD pattern, shown in Fig.8. Therefore, we can determine that there is transformer insulation failure in phase A. combined with ultrasonic location, the location of partial discharge can be detected.C. Rrsult of Electical-ultrasonic DetectionWith ultrasonic signals of transformer insulation fault received by each sensors, and three-dimensional scatter plot of partial discharge point, we can see that there is partial discharge in the vicinity of comic high seat of transformer phase. According to partial discharge test done at the same time, we knew the number of transformer partial discharge is far exceeds the partial discharge limits in the national standard. Electrical-ultrasonic can test the number and location of discharge. It good to prevent accidents caused by transformer insulation failure and to carry out repair work. CONCLUSIONA method of electical-ultrasonic detection is presented in this paper, which is effective to locate transformer insulation fault. A case is introduced to validate the accuracy of electical-ultrasonic detection. Detecting ultrasonic signal produced by PD can locate the discharge, but this method can not test the number of discharge. Partial discharge test can effectively test the discharge, but can not accurate locate. With electical-ultrasonic detection method, it is easy to locate PD and test the number of charge, which can effectively assess the status of transformer insulation.REFERENCES1 Xiaorong Wang, Bei Wei, Guanjun Wang. A new partial discharge electrical location method of transformer winding. High Voltage Technology. 1999,25(3): 27-292 Bengtsson C. Status and trends in transformer monitoring. IEEE Transaction on Power Delivery. 1996,11(3):1379-13843 Tatsuo Takada, Acoustic and Optical Method for Measuring Electric Charge Distributions in Dielectrics. IEEE transactions on Dielectrics and Electrical Insulation, 1999, 6(5):519-5474 Caixin