雷电冲击和VFTO在变压器绕组上分布的研究

发布时间：2018-06-19 12:46

本文选题：雷电冲击 + 特快速暂态过电压　；参考：《太原理工大学》2017年硕士论文

【摘要】：本文主要研究了雷电冲击电压和特快速暂态过电压(VFTO)在变压器绕组中的分布。相比于雷电冲击电压波,特快速暂态过电压的波前时间更短,且由频谱分析可知,特快速暂态过电压包含的频率更高,所以需要建立不同的模型进行分析。变压器在变电站中的作用很大,绕组内绝缘发生击穿后不能自行恢复,所以会造成极大的经济损失。现在变压器大部分采用氧化锌避雷器进行防雷保护,然而避雷器的制作工艺、绝缘老化和恶劣天气等因素都会影响避雷器的正常动作。此外,实际雷电统计中,变压器多受雷电入侵的影响,且避雷器经常误动作,所以变压器的防雷保护不能只靠避雷器,应该在绕组内部也加强自身的绝缘防护。雷电冲击电压波的波前时间为微秒级,其频率分量主要集中在0~50 kHz,所以以线饼为单位建立了变压器绕组的等值电路,这样既保证了计算精度,同时简化了运算,加快了求解速度;然后求解了等值电路模型中各个元件的参数;最后采用Bergeron等值模型法仿真计算了各种雷电冲击下变压器绕组中的过电压分布。通过实例仿真计算得到,波前时间和波尾时间分别主要影响变压器绕组的纵绝缘和主绝缘强度;雷电冲击截波可弥补波前时间延长的缺陷;计及工频电压下,当叠加的工频电压与标准雷电冲击电压的幅值极性相反时,变压器绕组的过电压分布情况最严重,此时对主、纵绝缘的考核比纯标准雷电入侵更加严格。此外,还提出了两种改善变压器绕组电位分布的措施,即对地电容电流补偿和纵向电容补偿,并通过实例进行了验证。特快速暂态过电压(VFTO)也是造成变压器绕组绝缘损坏的原因之一。特快速暂态过电压与雷电冲击过电压相比,波形陡度大,即波形上升时间为ns级,而雷电冲击过电压为μs级。其高频部分包含的频率高达50 MHz,极高频部分高达100 MHz,所以不能采用雷电冲击下的集中参数模型。针对特快速暂态过电压的特征,建立了变压器绕组的高频模型,然后采用频域法仿真计算了变压器绕组中的过电压分布。通过仿真计算得到,在靠近VFTO入侵的前几段线匝中容易发生绝缘击穿,所以应加强此处的绝缘防护。
[Abstract]:The distribution of lightning impulse voltage and very fast transient overvoltage VFTO in transformer windings is studied in this paper. Compared with the lightning impulse voltage wave, the wave front time of the very fast transient overvoltage is shorter, and from the spectrum analysis, the frequency of the ultra fast transient overvoltage is higher, so different models should be established to analyze it. The transformer plays a very important role in the substation, and the insulation in the winding can not be recovered by itself after breakdown, so it will cause great economic losses. Nowadays, most transformers use zinc oxide arresters for lightning protection. However, the normal operation of lightning arresters will be affected by the process of making lightning arresters, aging insulation and bad weather. In addition, in the actual lightning statistics, transformers are often affected by lightning intrusion, and lightning arresters often misoperate. Therefore, the lightning protection of transformers should not rely solely on lightning arresters, but should also strengthen their own insulation protection inside the windings. The wave front time of lightning impulse voltage wave is microsecond order, and its frequency component is mainly concentrated at 0 ~ 50 kHz. Therefore, the equivalent circuit of transformer winding is established in the unit of wire cake, which not only guarantees the calculation accuracy, but also simplifies the calculation. The solution speed is accelerated and the parameters of each component in the equivalent circuit model are solved. Finally, the overvoltage distribution in transformer windings under various lightning shocks is simulated by Bergeron equivalent model method. The simulation results show that the wave front time and the wave tail time mainly affect the longitudinal insulation and the main insulation strength of the transformer windings, the lightning impingement truncation can make up the defects of the wave front time extension, and the power frequency voltage is taken into account. When the superposition of the power frequency voltage is opposite to the amplitude polarity of the standard lightning impulse voltage, the overvoltage distribution of the transformer windings is the most serious, and the assessment of the main and longitudinal insulation is more strict than that of the pure standard lightning intrusion. In addition, two measures to improve the potential distribution of transformer windings are put forward, that is, the compensation of the earth capacitance current and the compensation of the longitudinal capacitance. Very fast transient overvoltage (VFTO) is also one of the causes of transformer winding insulation damage. Compared with the lightning impulse overvoltage, the waveform steepness is larger, that is, the rise time of the waveform is ns, and the lightning impulse overvoltage is 渭 s. The frequency of the high frequency part is as high as 50 MHz and that of the very high frequency part is up to 100 MHz, so the centralized parameter model under lightning shock cannot be adopted. According to the characteristics of ultra fast transient overvoltage, the high frequency model of transformer winding is established, and then the over-voltage distribution in transformer winding is simulated by frequency domain method. The simulation results show that insulation breakdown is easy to occur in the first few turns near the VFTO invasion, so the insulation protection should be strengthened here.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM41

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