Discussion on the standard of dielectric loss fact

2022-08-24
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Discussion on the standard of dielectric loss factor of film paper composite insulation capacitor

Abstract: the dielectric mode of film paper composite insulation coupling capacitor and capacitor voltage divider is integrated by Foshan Electric Power Industry Bureau: 1 According to the analysis of the test results of the loose loss factor of the data information, it is considered that the on-site test standard of the dielectric loss factor of the high-voltage film paper composite insulation capacitor is not greater than 0.2%, which is too strict, and it is recommended to relax the implementation. It is pointed out that QS1 Xilin bridge is not suitable for testing the dielectric loss factor of film paper composite insulation capacitor, and frequency conversion bridge is recommended; The contact resistance of high voltage leads will bring obvious error to the dielectric loss factor of film paper composite insulation capacitor

key words: film paper composite insulation capacitor dielectric loss factor standard film paper composite insulation capacitor is more and more widely used. At present, Foshan Electric Power Industry Bureau is running 110 kV and above coupling capacitor and capacitive voltage transformer TVC voltage divider, about only more than 10 are oil paper insulation capacitors, and the rest more than 200 are film paper composite capacitors (model OWF). Document [1] stipulates that the dielectric loss factor of film paper composite insulation coupling capacitor and capacitive voltage divider is not greater than 0.2% at 10 kV voltage. Document [2] requires that the dielectric loss factor measured at the ambient temperature of 20 ℃ under the rated power frequency voltage is not greater than 0.12% (three papers and two films) and 0.10% (two papers and two films). After the film paper composite capacitor that passed the preventive test still exploded, some units even required that the dielectric loss factor of the handover test should not be greater than 0.10% and that of the preventive test should not be greater than 0.15%. Through a large number of field tests, we believe that the standard is too strict for field tests and impractical, especially when measured with QS1 bridge, almost half of it cannot meet the requirements. This paper will discuss the problems we encountered in the field test

1qs1 bridge test

before the 1990s, oil paper insulated capacitors were basically used for coupling capacitors and capacitive voltage dividers. The requirements of the old preventive test standards were relatively loose, and the dielectric loss factor was tan δ It is required to be no more than 0.5%. In the past, QS1 Xilin bridge was widely used by power supply and consumption units for dielectric loss factor test. As we all know, the error of QS1 Xilin bridge instrument itself reaches ± 0.3%, and increases with the increase of the capacitance CX of the test object. When QS1 Xilin bridge is used to test oil paper insulated capacitor, the problem is not very prominent because the standard value of its dielectric loss factor (0.5%) is large. However, when testing the film paper composite insulation capacitor, it was found that the dielectric of many capacitors. This kind of experimental machine is the mainstream product of today's universal data experimental machine. The loss factor exceeded the standard, and even exceeded the requirements of the specification [1] at the time of handover. Table 1 shows the statistics of the results of the handover and preventive tests of film paper composite insulated capacitors and oil paper insulated capacitors with QS1 Xilin bridge by Foshan Electric Power Bureau

note: the capacitor is calculated by the number of sections, and the unit that independently measures the dielectric loss factor during the test is counted as one section. For example, when the next section of TVC is tested, the capacitors c1n and C2 on both sides of the tap of the intermediate transformer are tested separately, which is counted as two sections

in the unqualified film paper composite insulation capacitor in Table 1, 0.3% ≤ Tan δ< 15 knots with 0.4%, 0.4% ≤ Tan δ< 0.5% of 3 knots, Tan δ ≥ 0.5% of 4 sections (0.4% ≤ Tan δ< 0.5% have been replaced), while the dielectric loss factor of most unqualified capacitors (53 sections) is between 0.2% and 0.3%

theoretically, polypropylene film and capacitor paper composite impregnated organic synthetic insulating oil medium are used to replace capacitor paper impregnated mineral oil medium for film paper composite insulated capacitor. The active power loss is low, which is only about 1/4 of oil paper insulated capacitor, and the dielectric loss factor should be less than 0.1%, because the dielectric loss factor of polypropylene roughened film capacitor is only 0.01%, and the loss is 1/10 of capacitor paper, The dielectric loss factor of organic synthetic impregnant is only 0.03%. The field test found that the dielectric loss factor of film paper composite insulation capacitor greatly exceeded 0.1%, even exceeded the standard. There are two possibilities: first, manufacturing reasons, such as poor welding of lead terminals, poor contact between lead sheet and aluminum foil, burr, easy to cause discharge, uneven aluminum foil or film, poor impregnation, etc., will cause the dielectric loss factor to increase; Another reason is the test process or instrument. If the ex factory test value of dielectric loss factor is small and the field test value is large, the complexity of the field test should be considered

2 test of frequency conversion bridge and frequency converter on electrical appliances

2.1 introduction of two frequency conversion bridges

in order to truly measure the dielectric loss factor of membrane paper insulated capacitors, Foshan Electric Power Industry Bureau successively purchased three split AI-6000 frequency conversion bridges and one M4000 frequency conversion bridge of American doble company in 1999. Both are M-type bridges, using line frequency modulation measurement technology, with an output of (50 ± 5) Hz or 50 × The dielectric loss factor at 50Hz can be obtained by averaging the sine wave of (1 ± 0.05) Hz. The test accuracy of dielectric loss factor of split AI-6000 variable frequency bridge reaches 0.02%. It adopts photoelectric transmission signal and has strong anti-interference ability. The test data under strong interference on site are shown in Table 2; The test accuracy of the m-4000 frequency conversion bridge is 0.01%, and the on-site anti-interference ability is stronger. The m-4000 frequency conversion bridge can maintain the technical requirements under the interference of 20 times the current of the test object, and can resist 500 μ T power frequency electromagnetic interference. For example, in the 500 kV site, during the dielectric loss factor test of 500 kV current transformer and voltage equalizing capacitor, the interference voltage measured by electrostatic voltmeter on the test object is as high as 12 ~ 15 kV, which has exceeded the test voltage of the bridge. Even if equipped with an electronic phase shifter, the QS1 bridge cannot be balanced at all. When tested with a frequency conversion bridge, the data is stable and basically does not change with the interference voltage

2.2 test of dielectric loss factor

we retested all film paper composite insulation capacitors of Foshan Electric Power Industry Bureau with AI-6000 or m-4000 frequency conversion bridge. Among them, c1n and C2 of TVC lower section capacitors without medium voltage lead-out terminals were tested by self excitation method, and a few capacitors with medium voltage lead-out terminals in Guilin electric power capacitor factory were still measured by positive connection method. The measurement results are shown in Table 3. The test results show that the dielectric loss factor of most film paper composite insulation capacitors is less than 0.2%

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