交直流复合电场下界面电荷对油纸绝缘沿面放电的影响

发布时间：2018-03-07 01:38

  本文选题：换流变压器　切入点：交直流复合电场　出处：《华北电力大学(北京)》2014年博士论文　论文类型：学位论文

【摘要】：换流变压器是高压直流输电系统的重要设备之一,其绝缘的安全可靠对整个直流输电系统的稳定运行至关重要。换流变压器在直流输电系统中连接换流阀的组别不同,其阀侧绕组将承受不同直流极性、不同交流、直流比例的复合电场。这种复合电场会导致油纸绝缘介质内部和交界面产生空间电荷/界面电荷积聚,形成空间电荷场,影响换流变压器绝缘介质的电场分布。空间电荷的积聚与外施电压形式、电场大小、绝缘介质的温度、水分等多种因素相关,导致了换流变压器的电场分布呈现出非线性、各向异性的特点,并且换流变压器还存在极性反转的特殊运行工况,这些条件下油纸的绝缘特性与空间电荷/界面电荷密切相关。油纸绝缘的沿面闪络电场强度远低于体击穿电场强度,因此油纸绝缘的沿面电气绝缘特性对于换流变压器油纸绝缘结构的整体绝缘性能和可靠性极为关键,界面电荷对油纸绝缘沿面放电的影响直接关系到沿面绝缘特性,但其作用机理仍不明晰。论文设计构建了交直流复合电场油纸绝缘试验平台,包括交直流复合电源装置、变压器油密闭循环及处理装置、油纸绝缘沿面放电数据采集系统、油纸绝缘界面电荷测量平台和极性反转试验装置。油纸绝缘界面电荷测量平台能够测量非均匀电场的油纸界面电荷积聚、消散及分布特性,其最小空间分辨率为1mm2,测量灵敏度0.129pC/mm2;极性反转试验装置的反转时间为ms级,符合换流变压器实际运行中发生极性反转的时间。针对油纸绝缘沿面放电模型研究了油纸界面电荷的特性,得到了在交直流复合电场条件下,油纸绝缘界面电荷的积聚、消散和波动规律。油纸界面积聚的电荷极性与施加的直流电压分量极性相同,直流成份比例越高,其电荷密度的累积效应越大,油纸界面积聚的电荷密度也越大；沿面绝缘结构的界面电荷90%密度值的积聚时间远小于平行绝缘结构,这种差异将导致换流变压器电压发生波动或极性反转时各绝缘结构承受的电压分配不均；界面电荷密度随交流电压瞬时值的变化产生类似工频的波动,波动的幅度随直流比例的增加而减小,在交直流分量比例1：1(AC有效值：DC平均值)时,界面电荷密度最大峰值能够达到平均值的1.8倍。交直流复合电场下油纸绝缘的沿面闪络电压比纯交流电压的沿面闪络电压高,且负极性直流叠加交流的沿面闪络电压比正极性直流叠加交流的沿面闪络电压要高。通过对针板沿面放电模型下界面电荷的测量结果分析,油纸绝缘积聚的同极性界面电荷能够削弱针电极附近的电场强度,从而提高了沿面闪络电压。随着直流比例的增加,沿面爬电发展过程的视在放电量、放电重复率和累积的视在放电能量呈明显的减小趋势,油纸界面从呈现碳化痕迹,到没有明显碳痕的演变。相同比例复合电场沿面爬电各发展阶段界面电荷的增长率随总视在放电量的增加而减小,这说明同极性的界面电荷能够抑制沿面爬电的发展,而沿面爬电可以削弱界面电荷的积聚。极性反转条件下的沿面闪络试验结果发现界面电荷能够大大降低极性反转时的沿面闪络电压,并提出了通过测量极性反转的沿面闪络电压获得表面电位系数k1k2来衡量油纸界面积聚电荷能力的方法。通过测量油纸沿面绝缘界面电荷在极性反转前后的密度变化,得到极性反转时刻界面电荷产生的电场和极性反转后的外施电场叠加能够加强针电极处的最大合成场强；发现沿面绝缘结构的界面电荷在极性反转过程中只需数百ms就反转为外施电压的极性,远小于IEC61378-2标准中换流变压器出厂的极性反转试验电压规定的反转时间(小于2min),建议采用CIGRE的电压陡变试验波形(反转时间小于2ms)进行考核。发现了水分、温度的增加,油纸绝缘界面电荷密度减小,油纸绝缘沿面爬电的放电起始电压大幅度降低、沿面闪络电压下降,放电重复率、总视在放电量增加。测量了油浸纸板表面电导率,发现温度、水分的增加会导致油浸纸板的表面电导率急剧增加,电荷的迁移速率增加,使得界面电荷消散速度加快,减小了界面电荷积聚,削弱了对沿面爬电的抑制作用。通过对油纸界面电荷特性的研究,提出了基于电荷特性的换流变压器油、纸绝缘性能评估方法,为换流变压器绝缘设计的材料选取提供了新的评估手段。
[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.

【学位授予单位】：华北电力大学(北京)
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM855
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本文编号：1577423