Process Research On Complex Electric Field Between Turn To Turn Partial Discharge In AC-DC Converter Transformer

Converter transformer as one the core equipment of the UHVDC transmission system,it plays an irreplaceable role in HVDC systems. With a different AC adapter, converter transformer valve winding long withstand AC, DC, AC-DC composite electric field effect, which oil-paper insulation by more severe test. Interturn insulation converter transformer winding insulation as the weak link, the operation reliability are highly valued, but now on a composite voltage converter transformer partial discharge characteristics, as well as turn insulation oil in water content, oil temperature, oil on different discharge characteristics unclear.In this paper, the experimental platform to build a converter transformer in strict accordance with the actual operation, the converter transformer for the factory test and run the interturn insulation interturn model studied under AC and DC electric field of complex partial discharge development process. The main contents include AC and DC voltage interturn Composite partial discharge; the impact of changes in moisture content in transformer oil to turn partial discharge between the converter transformer; and oil were 80℃,50℃,20℃ turn when changing rheological 25 Karamay oil, Shell Diala S3 No. oil flow on the exchange between the partial discharges of turns; between partial discharge situation. The above study provides a theoretical basis for oil-paper insulation strength for oil-paper insulation converter transformer fault diagnosis basis.The results show that with the increase of AC and DC voltage in the DC component of the composite, the discharge phase of the positive half cycle departing from the negative half-cycle, the firing voltage and near breakdown voltage increases, the growth rate slowed discharge, reduce discharge severity; characteristics of various types of gas under AC voltage gas production was significantly higher than under AC and DC voltage gas production complex. Starting voltage AC-DC composite voltage 1 to 1 ratio under 20% AC voltages, AC-DC composite voltage 1 to 3 AC voltages lower than 40%, AC-DC composite voltage of 1 to 5 at voltages higher than AC 200%; close to the breakdown voltage, AC-DC composite voltage at 1 to 1 ratio of 122.2 percent higher AC voltages, AC and DC voltage of 1 to 3 complex than AC voltages at high 155.6%. The AC voltage unit and discharge times were 1 to 1 AC-DC, AC-DC 12.9 times and 20.65 times of 1 to 3; the total discharge amount of the AC voltage AC and DC are 1 to 1, AC-DC 46.6 times and 49.51 to 3 times. C2H2 gas production under the AC voltage of 1 to 1.35 times a composite voltage,1 to 4.3 times the 3 complex voltage. The reason is complex electric field increases with the polarity of the DC component so that the accumulation of interfacial charge oilpaper interface weakened form of a reverse electric field strength of the electric field near the electrode, the higher the DC component ratio, the greater the accumulation of oil-paper interface charge density, suppression discharging.Increase the moisture content in transformer oil makes its discharge level becomes severe, increasing the number of discharges, and discharges relatively steady rise over time, as the unit time maximum discharge capacity has been maintained at a certain level, starting voltage and breakdown voltage is lowered close; with the discharge development C2H6 gas production gap is most obvious. 26.9ppm moisture content in transformer oil than oil when the moisture content 9.8ppm when inception voltage drop 57.14 percent, close to the breakdown voltage drops to 62.5%. High total discharge amount of water is 1.46 times of low water. The reason for the interface charge with increasing moisture content greaseproof paper presents a decreasing trend, oil-paper insulation interface charge density decreased, the inhibition of the decline of the electric field, the discharge increased.Increased transformer oil makes interturn discharge starting voltage and phase voltage breakdown near the lower discharge level becomes severe, increasing the number of discharges, a sharp increase discharge capacity, maximum up to 1500 times, various types of gas with increasing temperature Yield increases. Transformer oil at 50 ℃, the initial discharge voltage dropped 71.4% oil temperature at 20 ℃, when approaching the breakdown phase voltage and oil temperature 20 ℃ close; oil temperature of 80 ℃, the initial discharge voltage drop oil 20 57.1% ℃ when, near the breakdown phase voltage drop of the oil temperature at 20 ℃ 69.5%. Oil temperature of 80 ℃, discharge development accelerated, with only four experimental stage breakdown. Discharge repetition rate, the oil temperature is 80℃ test oil temperature 50℃ 40 times, and 100 times of the oil temperature 20 ℃. The total amount of discharge, the oil temperature is 80℃ experiment 1500 times for 20℃ oil, oil temperature 50℃ experiment is 60 times the oil temperature of 20℃. CH4 and C2H2 with increasing temperature gap is most pronounced. The reason for the interface charge density increases with temperature show a downward trend, the inhibitory effect of the electric field is reduced, the discharge increased.Transformer oil Karamay on the 25th with the inception voltage and breakdown voltage than the adjacent Shell Diala S3 No. oil lower, more intense discharge level, unit and total discharge amount and discharge times have increased, the development of more rapid discharge. Karamay oil transformer with the 25th, the initial discharge voltage lower than the number of Shell Diala S3 transformer oil was 57.14%; close to the breakdown voltage, the 25th Karamay oil decreased to 62.5%.