本文選題：換流變壓器　切入點：交直流復合電場　出處：《華北電力大學(北京)》2014年博士論文　論文類型：學位論文

【摘要】：換流變壓器是高壓直流輸電系統(tǒng)的重要設備之一,其絕緣的安全可靠對整個直流輸電系統(tǒng)的穩(wěn)定運行至關重要。換流變壓器在直流輸電系統(tǒng)中連接換流閥的組別不同,其閥側繞組將承受不同直流極性、不同交流、直流比例的復合電場。這種復合電場會導致油紙絕緣介質內部和交界面產(chǎn)生空間電荷/界面電荷積聚,形成空間電荷場,影響換流變壓器絕緣介質的電場分布�？臻g電荷的積聚與外施電壓形式、電場大小、絕緣介質的溫度、水分等多種因素相關,導致了換流變壓器的電場分布呈現(xiàn)出非線性、各向異性的特點,并且換流變壓器還存在極性反轉的特殊運行工況,這些條件下油紙的絕緣特性與空間電荷/界面電荷密切相關。油紙絕緣的沿面閃絡電場強度遠低于體擊穿電場強度,因此油紙絕緣的沿面電氣絕緣特性對于換流變壓器油紙絕緣結構的整體絕緣性能和可靠性極為關鍵,界面電荷對油紙絕緣沿面放電的影響直接關系到沿面絕緣特性,但其作用機理仍不明晰。論文設計構建了交直流復合電場油紙絕緣試驗平臺,包括交直流復合電源裝置、變壓器油密閉循環(huán)及處理裝置、油紙絕緣沿面放電數(shù)據(jù)采集系統(tǒng)、油紙絕緣界面電荷測量平臺和極性反轉試驗裝置。油紙絕緣界面電荷測量平臺能夠測量非均勻電場的油紙界面電荷積聚、消散及分布特性,其最小空間分辨率為1mm2,測量靈敏度0.129pC/mm2;極性反轉試驗裝置的反轉時間為ms級,符合換流變壓器實際運行中發(fā)生極性反轉的時間。針對油紙絕緣沿面放電模型研究了油紙界面電荷的特性,得到了在交直流復合電場條件下,油紙絕緣界面電荷的積聚、消散和波動規(guī)律。油紙界面積聚的電荷極性與施加的直流電壓分量極性相同,直流成份比例越高,其電荷密度的累積效應越大,油紙界面積聚的電荷密度也越大；沿面絕緣結構的界面電荷90%密度值的積聚時間遠小于平行絕緣結構,這種差異將導致?lián)Q流變壓器電壓發(fā)生波動或極性反轉時各絕緣結構承受的電壓分配不均；界面電荷密度隨交流電壓瞬時值的變化產(chǎn)生類似工頻的波動,波動的幅度隨直流比例的增加而減小,在交直流分量比例1：1(AC有效值：DC平均值)時,界面電荷密度最大峰值能夠達到平均值的1.8倍。交直流復合電場下油紙絕緣的沿面閃絡電壓比純交流電壓的沿面閃絡電壓高,且負極性直流疊加交流的沿面閃絡電壓比正極性直流疊加交流的沿面閃絡電壓要高。通過對針板沿面放電模型下界面電荷的測量結果分析,油紙絕緣積聚的同極性界面電荷能夠削弱針電極附近的電場強度,從而提高了沿面閃絡電壓。隨著直流比例的增加,沿面爬電發(fā)展過程的視在放電量、放電重復率和累積的視在放電能量呈明顯的減小趨勢,油紙界面從呈現(xiàn)碳化痕跡,到?jīng)]有明顯碳痕的演變。相同比例復合電場沿面爬電各發(fā)展階段界面電荷的增長率隨總視在放電量的增加而減小,這說明同極性的界面電荷能夠抑制沿面爬電的發(fā)展,而沿面爬電可以削弱界面電荷的積聚。極性反轉條件下的沿面閃絡試驗結果發(fā)現(xiàn)界面電荷能夠大大降低極性反轉時的沿面閃絡電壓,并提出了通過測量極性反轉的沿面閃絡電壓獲得表面電位系數(shù)k1k2來衡量油紙界面積聚電荷能力的方法。通過測量油紙沿面絕緣界面電荷在極性反轉前后的密度變化,得到極性反轉時刻界面電荷產(chǎn)生的電場和極性反轉后的外施電場疊加能夠加強針電極處的最大合成場強；發(fā)現(xiàn)沿面絕緣結構的界面電荷在極性反轉過程中只需數(shù)百ms就反轉為外施電壓的極性,遠小于IEC61378-2標準中換流變壓器出廠的極性反轉試驗電壓規(guī)定的反轉時間(小于2min),建議采用CIGRE的電壓陡變試驗波形(反轉時間小于2ms)進行考核。發(fā)現(xiàn)了水分、溫度的增加,油紙絕緣界面電荷密度減小,油紙絕緣沿面爬電的放電起始電壓大幅度降低、沿面閃絡電壓下降,放電重復率、總視在放電量增加。測量了油浸紙板表面電導率,發(fā)現(xiàn)溫度、水分的增加會導致油浸紙板的表面電導率急劇增加,電荷的遷移速率增加,使得界面電荷消散速度加快,減小了界面電荷積聚,削弱了對沿面爬電的抑制作用。通過對油紙界面電荷特性的研究,提出了基于電荷特性的換流變壓器油、紙絕緣性能評估方法,為換流變壓器絕緣設計的材料選取提供了新的評估手段。
[Abstract]:Converter transformer is one of the important equipment in HVDC system, the insulation safety on the HVDC system steady operation is very important. The converter transformer in HVDC converter valve system connected to different groups, the valve side winding will be under different DC polarity, different AC DC electric field, composite proportion. The composite electric field causes insulation medium and interface generated space charge / interfacial charge accumulation, the formation of space charge field, the effect of electric field change of dielectric transformer. The distribution of the space charge accumulation and the external applied voltage, the electric field, the insulation medium temperature, moisture and other factors, led to the distribution of the electric field change the current transformer is nonlinear, anisotropic characteristics, and for the special operating condition of transformer has polarity reversal, insulating oil paper under these conditions The characteristics of space charge and interface charge / closely related. Insulation flashover field strength is much lower than the breakdown field strength, so insulation surface insulation for converter transformer oil paper insulation insulation performance and reliability of the whole structure is the key field of surface charge effect of insulation surface discharge of oil paper directly the surface insulation properties, but the mechanism is not clear. The design of compound AC-DC electric field insulation test platform, including AC / DC hybrid power supply device, transformer oil circulation and processing device, insulation surface discharge data acquisition system, interface charge measurement platform and polarity reversal test device of oil paper insulation. Insulation interface charge measurement platform to the oil paper interface charge accumulation measurement of non uniform electric field, dissipation and distribution characteristics, the minimum spatial resolution rate was 1 Mm2, the measurement sensitivity of 0.129pC/mm2; time reversal polarity reversal test device for ms level, in line with the converter transformer polarity reversal occurs in the actual operation time. The surface discharge model to study the characteristics of oil paper interface charge oil paper insulation, obtained under combined AC and DC electric field under the condition of interfacial charge accumulation of insulation, dissipation and fluctuation of the DC voltage component. The charge oil pressboard interface with the polarity of the applied DC component of the same polarity, the higher the proportion, the cumulative effect of the charge density of the charge density, the greater the oil pressboard interface; surface insulation interface charge density structure 90% value accumulation time is far less than the parallel this difference will lead to the insulation structure of converter transformer voltage fluctuation or polarity reversal voltage distribution of each insulation structure to withstand the uneven; interfacial charge density with AC voltage instantaneous value. The changes have a similar frequency fluctuations, increased volatility decreases with the proportion of DC, AC and DC component in the ratio of 1:1 (AC value: DC average), the interface charge density peak can reach 1.8 times the average. Under combined AC DC voltage insulation flashover voltage flashover ratio the high voltage AC voltage, and negative DC AC flashover voltage than the positive DC AC flashover voltage is higher. Through measuring the needle plate along the interface charge discharge model results, insulation of polar interface charge accumulation can weaken the intensity of electric field near the needle electrode thus, improving surface flashover voltage. With the increase of DC ratio, surface creepage development process as in the discharge, discharge repetition rate and cumulative apparent decreased in the discharge energy, oil The interface from the present to the evolution of carbide traces, no obvious traces of carbon. The same proportion of composite field along the increased surface creepage at various stages of interfacial charge growth rate with the total apparent discharge quantity decreases, the interfacial charge polarity can inhibit the development of surface creepage, and surface creepage can weaken the interfacial charge accumulation. The flashover voltage of the interface charge can greatly reduce the polarity reversal of polarity reversal conditions that the flashover test results, and puts forward a method of using surface potential coefficient measurement of k1k2 polarity reversal for the flashover voltage to measure the oil pressboard interface. By measuring the charge capacity of oil pressboard in the surface of the insulation interface charge density changes before and after the polarity reversal, get the polarity reversal moment generated interface charge after polarity reversal electric field and the applied electric field superposition can enhance the maximum needle electrode at Synthetic field; found along the surface of the insulation structure of the interface charge only hundreds of MS in polarity reversal process in reverse the polarity of the applied voltage, reverse polarity reversal test time is far less than the predetermined voltage converter transformer factory in IEC61378-2 standard (less than 2min), the recommended test voltage waveform with CIGRE (the reversal time is less than 2ms). The assessment found water, increasing temperature, interfacial charge density decreases the discharge start voltage insulation, greatly reduce the surface creepage insulation, decrease the flashover voltage, discharge repetition rate, total apparent increase in the discharge. Oil immersed pressboard surface conductivity, it is found that the temperature. Measurement of water will lead to the increase of the surface conductivity of oil paperboard increased sharply, the migration rate of the charge increases, the interfacial charge dissipation speed, reduce the interfacial charge accumulation, the weakening of surface creepage Based on the study of the interfacial charge characteristics of oil paper, a method of evaluating the insulation performance of converter transformer oil and paper based on charge characteristics is put forward, which provides a new evaluation method for material selection of insulation design of converter transformer.

【學位授予單位】：華北電力大學(北京)
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TM855
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本文編號：1577423