换流变压器油纸绝缘击穿特性
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摘要
换流变压器是高压直流输电系统中的关键设备之一，由于承受交流、直流、直流叠加交流以及极性反转等电压作用，其阀侧主绝缘出厂试验和运行中都有较高的故障率。国内外学者针对换流变压器绝缘问题开展了大量的试验研究或电场仿真，但研究内容还不够完善，也有少量研究结果出现了相互矛盾的结论。因此，有必要对换流变压器油纸绝缘特性进行更深入研究。
本文利用RC模型对多种电压下油纸复合绝缘电压分布特性进行了数学分析，讨论了电压分布对绝缘击穿的影响。设计了直流叠加交流及极性反转高压试验装置，以平板电极为基本试验电极模型，在不同间隙和不同温度下对油隙、浸油纸板和油纸复合绝缘样品进行了交流、直流、直流叠加交流和极性反转电压击穿试验研究。在此基础上进一步探讨了换流变压器油纸绝缘击穿机理，并对换流变压器阀侧主绝缘技术进行了分析。
研究结果表明，在RC模型下直流升压和极性反转过程将引起油纸复合绝缘内部油隙的电压暂态升高，其幅值决定于外施电压变化速度与持续时间、充电时间常数和绝缘电阻比值。任一温度下变压器油直流叠加交流击穿电压高于交流击穿电压，变压器油交流击穿电压温度特性与直流和极性反转击穿电压温度特性有较大区别。随交流分量增加浸油纸板的直流叠加交流击穿电压迅速下降，低温下极性反转会造成浸油纸板击穿电压降低，这些现象证实浸油纸板也是一种纸板和油孔构成的复合绝缘。不同交流分量下油纸复合绝缘直流叠加交流击穿电压出现了明显的极大值点，本文认为它是由浸油纸板击穿引起油纸复合绝缘击穿与由油隙击穿引起油纸复合绝缘击穿的分界点。低温下极性反转造成油纸复合绝缘击穿电压明显降低，极性反转速度越快越严重。极性反转电压下油纸复合绝缘吸收电流初始值、衰减函数和积累电荷量偏离了RC模型确定的规律，且与所施加电压幅值相关。
总结试验结果发现直流和极性反转电压下油纸绝缘击穿特性不能用现有击穿理论解释，利用空间电荷积聚与消散过程及其对电场分布影响能解释这些现象。认为通过出厂交流和直流试验的换流变压器阀侧主绝缘能够胜任稳态运行条件，由于浸油纸板击穿电压随交流分量增加快速下降，油隙闪络使浸油纸板承受电压幅值及其交流分量百分数提高会造成油纸复合绝缘击穿，所以有必要对变压器油进行严格净化和运行监测。极性反转暂态特性及其与施加电压的非线性关系要得到足够重视，应尽量避免低温下快速极性反转，随6脉动桥数增加，极性反转试验电压幅值会高于交流试验电压幅值，为承受这种极性反转电压作用应该适当增大油隙尺寸。
The converter transformer is one of key equipments in the HVDC transmissionsystem. Because of withstanding AC, DC, AC+DC(AC and DC), polarity reversalvoltage and so on, the main insulation on valve side has a higher fault ratio duringboth the factory test and the operation. A large number of experiments and electricalfield simulation studies on the oil and paper insulation of the converter transformerare carried out by researchers at home and aboard, but it is not sufficient, and asmall number of results are contradictory. Therefore, more research oncharacteristics of the oil and pressboard insulation in the converter transformer isnecessary.
Mathematical analysis on characteristic of voltage distribution in the oil-pressboard insulation by RC model is carried out in this paper, and the effect of thevoltage distribution on the insulation breakdown is discussed. Both AC+DC andpolarity reversal high voltage equipments are designed. Breakdown experimentsunder AC, DC, AC+DC and polarity reversal voltage on the transformer oil, oil-immersed pressboards and the oil-pressboard insulation are accomplished withdifferent gaps and temperatures by a pair of plane electrodes as the basic model.Based on these, the breakdown mechanism of the converter transformer oil andpressboard insulation is further discussed, and the technology about the convertertransformer main insulation on valve side is analyzed.
Research results indicate that, DC voltage increase and polarity reversal cancause a transient increase of the voltage on oil gaps in the oil-pressboard insulation,and the voltage amplitude depends on varying speed and duration of applied voltage,charging time constant and ratio of insulation resistance. AC+DC breakdownvoltage of the transformer oil is higher than AC breakdown voltage at anytemperature，and breakdown voltage temperature characteristics under AC voltage are different from those under DC and polarity reversal voltage. AC+DC breakdownvoltage of oil-immersed pressboards decrease rapidly along with the increase of ACcomponent, and polarity reversal can decrease breakdown voltage at lowtemperature. These prove that the oil-immersed pressboard is also a kind ofcomposite insulation which is composed of pressboards and oil holes.It has a clearmaximum value among breakdown voltage of the oil-pressboard insulation underAC+DC voltage with different AC component, which is considered to be a boundarybetween the oil-pressboard insulation breakdown caused by the oil-immersedpressboard breakdown and caused by the oil gaps breakdown. Polarity reversaldecreases breakdown voltage of the oil-pressboard insulation at low temperature, thefaster the polarity reversal is, the more serious it is. Initial values of absorptioncurrents, attenuation functions and accumulated charges of the oil-pressboardinsulation under polarity reversal voltage deviate from laws determined by the RCmodel, and it is related to the amplitude of applied voltage.
It is found by summarizing experiment results that the breakdowncharacteristics of the oil and pressboard insulation under DC and polarity reversalvoltage can not be explained by the existing breakdown theory, which can beexplained by the process of space charge accumulation and dissipation and itsinfluence on the distribution of the electrical field. It is considered that the maininsulation of the converter transformer on valve side which has passed the factorytest is adequate for the steady-state operating conditions, because of the rapiddecrease of the oil-immersed pressboard breakdown voltage along with the increaseof the AC component, the flashover of oil gaps will enhance the voltage amplitudeand the AC component percentage bearing by the oil-immersed pressboard, whichmay cause the oil-pressboard insulation breakdown. Therefore, the strict purificationand operational monitor for the converter transformer oil is necessary. Enoughattention should be attached to the transient characteristic by polarity reversal and itsnonlinear relationship with the applied voltage. The rapid polarity reversal at lowtemperature must be avoided to the greatest extent. The voltage amplitude of thepolarity reversal test will be higher than that of the AC test along with the increaseof the6-impulse-bridge number, so the thickness of oil gaps should be appropriatelyincreased to bear this polarity reversal voltage.
本文利用RC模型对多种电压下油纸复合绝缘电压分布特性进行了数学分析，讨论了电压分布对绝缘击穿的影响。设计了直流叠加交流及极性反转高压试验装置，以平板电极为基本试验电极模型，在不同间隙和不同温度下对油隙、浸油纸板和油纸复合绝缘样品进行了交流、直流、直流叠加交流和极性反转电压击穿试验研究。在此基础上进一步探讨了换流变压器油纸绝缘击穿机理，并对换流变压器阀侧主绝缘技术进行了分析。
研究结果表明，在RC模型下直流升压和极性反转过程将引起油纸复合绝缘内部油隙的电压暂态升高，其幅值决定于外施电压变化速度与持续时间、充电时间常数和绝缘电阻比值。任一温度下变压器油直流叠加交流击穿电压高于交流击穿电压，变压器油交流击穿电压温度特性与直流和极性反转击穿电压温度特性有较大区别。随交流分量增加浸油纸板的直流叠加交流击穿电压迅速下降，低温下极性反转会造成浸油纸板击穿电压降低，这些现象证实浸油纸板也是一种纸板和油孔构成的复合绝缘。不同交流分量下油纸复合绝缘直流叠加交流击穿电压出现了明显的极大值点，本文认为它是由浸油纸板击穿引起油纸复合绝缘击穿与由油隙击穿引起油纸复合绝缘击穿的分界点。低温下极性反转造成油纸复合绝缘击穿电压明显降低，极性反转速度越快越严重。极性反转电压下油纸复合绝缘吸收电流初始值、衰减函数和积累电荷量偏离了RC模型确定的规律，且与所施加电压幅值相关。
总结试验结果发现直流和极性反转电压下油纸绝缘击穿特性不能用现有击穿理论解释，利用空间电荷积聚与消散过程及其对电场分布影响能解释这些现象。认为通过出厂交流和直流试验的换流变压器阀侧主绝缘能够胜任稳态运行条件，由于浸油纸板击穿电压随交流分量增加快速下降，油隙闪络使浸油纸板承受电压幅值及其交流分量百分数提高会造成油纸复合绝缘击穿，所以有必要对变压器油进行严格净化和运行监测。极性反转暂态特性及其与施加电压的非线性关系要得到足够重视，应尽量避免低温下快速极性反转，随6脉动桥数增加，极性反转试验电压幅值会高于交流试验电压幅值，为承受这种极性反转电压作用应该适当增大油隙尺寸。
The converter transformer is one of key equipments in the HVDC transmissionsystem. Because of withstanding AC, DC, AC+DC(AC and DC), polarity reversalvoltage and so on, the main insulation on valve side has a higher fault ratio duringboth the factory test and the operation. A large number of experiments and electricalfield simulation studies on the oil and paper insulation of the converter transformerare carried out by researchers at home and aboard, but it is not sufficient, and asmall number of results are contradictory. Therefore, more research oncharacteristics of the oil and pressboard insulation in the converter transformer isnecessary.
Mathematical analysis on characteristic of voltage distribution in the oil-pressboard insulation by RC model is carried out in this paper, and the effect of thevoltage distribution on the insulation breakdown is discussed. Both AC+DC andpolarity reversal high voltage equipments are designed. Breakdown experimentsunder AC, DC, AC+DC and polarity reversal voltage on the transformer oil, oil-immersed pressboards and the oil-pressboard insulation are accomplished withdifferent gaps and temperatures by a pair of plane electrodes as the basic model.Based on these, the breakdown mechanism of the converter transformer oil andpressboard insulation is further discussed, and the technology about the convertertransformer main insulation on valve side is analyzed.
Research results indicate that, DC voltage increase and polarity reversal cancause a transient increase of the voltage on oil gaps in the oil-pressboard insulation,and the voltage amplitude depends on varying speed and duration of applied voltage,charging time constant and ratio of insulation resistance. AC+DC breakdownvoltage of the transformer oil is higher than AC breakdown voltage at anytemperature，and breakdown voltage temperature characteristics under AC voltage are different from those under DC and polarity reversal voltage. AC+DC breakdownvoltage of oil-immersed pressboards decrease rapidly along with the increase of ACcomponent, and polarity reversal can decrease breakdown voltage at lowtemperature. These prove that the oil-immersed pressboard is also a kind ofcomposite insulation which is composed of pressboards and oil holes.It has a clearmaximum value among breakdown voltage of the oil-pressboard insulation underAC+DC voltage with different AC component, which is considered to be a boundarybetween the oil-pressboard insulation breakdown caused by the oil-immersedpressboard breakdown and caused by the oil gaps breakdown. Polarity reversaldecreases breakdown voltage of the oil-pressboard insulation at low temperature, thefaster the polarity reversal is, the more serious it is. Initial values of absorptioncurrents, attenuation functions and accumulated charges of the oil-pressboardinsulation under polarity reversal voltage deviate from laws determined by the RCmodel, and it is related to the amplitude of applied voltage.
It is found by summarizing experiment results that the breakdowncharacteristics of the oil and pressboard insulation under DC and polarity reversalvoltage can not be explained by the existing breakdown theory, which can beexplained by the process of space charge accumulation and dissipation and itsinfluence on the distribution of the electrical field. It is considered that the maininsulation of the converter transformer on valve side which has passed the factorytest is adequate for the steady-state operating conditions, because of the rapiddecrease of the oil-immersed pressboard breakdown voltage along with the increaseof the AC component, the flashover of oil gaps will enhance the voltage amplitudeand the AC component percentage bearing by the oil-immersed pressboard, whichmay cause the oil-pressboard insulation breakdown. Therefore, the strict purificationand operational monitor for the converter transformer oil is necessary. Enoughattention should be attached to the transient characteristic by polarity reversal and itsnonlinear relationship with the applied voltage. The rapid polarity reversal at lowtemperature must be avoided to the greatest extent. The voltage amplitude of thepolarity reversal test will be higher than that of the AC test along with the increaseof the6-impulse-bridge number, so the thickness of oil gaps should be appropriatelyincreased to bear this polarity reversal voltage.
引文
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