110kV和220kV变压器中性点过电压仿真分析及其保护探究

发布时间：2019-03-04 17:28

【摘要】：目前我国110kV和220kV系统变压器普遍采用部分中性点接地方式运行,变压器中性点的过电压保护采取避雷器和放电间隙并联措施,但经现场运行发现存在绝缘配合失调的情况,最常见的故障是系统有效接地时发生单相接地故障却引起间隙误击穿,导致停电规模扩大；而棒间隙拒动导致避雷器爆炸和设备绝缘损坏的事故也多次发生,亟需进一步完善变压器中性点的接地方式,保证电力系统安全可靠运行。本文主要基于两种思路对此问题进行深入探究,第一种是变压器中性点采用小电抗接地方式,另一种是在目前中性点部分接地方式下,对避雷器和间隙的配合参数进行整定,并对目前间隙的改进工作提出建议。变压器经小电抗接地运行方式具有防止有效接地系统发生“失地”现象、限制变压器中性点短路电流和降低中性点过电压对系统绝缘损害的优势,且对中性点过电压的防护,也不再需要装设间隙,可有效避免间隙对系统带来的运行隐患。目前国内500kV自耦变压器中性点经小电抗接地方式经现场运行检验,效果良好,而110kV和220kV变压器中性点采用经小电抗接地方式运行还处在理论完善和现场试验阶段,各文献对此种方式接地看法不一,有必要对此问题做进一步的研究探讨,本文主要研究了系统接入小电抗后变压器及系统零序阻抗变化,并分析了其对中性点短路电流、系统零序阻抗和变压器中性点绝缘水平的影响；对接地小电抗的装置进行了设计和建议小电抗的取值范围为变压器零序阻抗的1/3。本文主要还对目前变压器中性点采用的部分接地方式进行优化和改进。经过对多起事故原因的分析研究,发现中性点处的保护参数整定应依据变压器中性点处实际过电压情况来进行选择,但目前用作避雷器和间隙整定参考的却是标准雷电波和工频电压波的放电电压,导致间隙和避雷器不能可靠保护中性点绝缘。本文在考虑了变电所现场运行的各项影响因素后,对在中性点上引起的雷电过电压和单相接地工频过电压的波形情况利用EMTP仿真软件进行仿真计算,得到的结论对间隙和避雷器参数进行整定；然而目前使用的棒间隙仍存在距离调节不准、同心度差和放电分散性高等缺点,其在遭受电弧作用时,电极发生烧蚀,棒间隙距离发生变化,使得间隙的使用频率较低,本文对间隙的改进也提出了自己的建议。
[Abstract]:At present, partial neutral grounding mode is generally used in China's 110kV and 220kV system transformers. The over-voltage protection of transformer neutral points takes measures of lightning arrester and discharge gap parallel. However, it is found that there is a misalignment of insulation coordination in the field operation. The most common fault is that the single-phase grounding fault occurs when the system is effectively grounded, but it causes the gap breakdown by mistake, which leads to the enlargement of the scale of the power outage. The accidents of lightning arrester explosion and equipment insulation damage caused by bar gap rejection also occur many times. It is urgent to further improve the grounding mode of transformer neutral point to ensure the safe and reliable operation of power system. The first is that the neutral point of transformer is grounded by small reactance, and the other is to adjust the matching parameters of lightning arrester and gap under the current partial grounding mode of neutral point, the first is that the neutral point of transformer is grounded by small reactance, and the other is to adjust the matching parameters of lightning arrester and gap under the current partial neutral grounding mode. At the same time, some suggestions are put forward for the improvement of the gap at present. The operation mode of transformer through small reactance earthing has the advantage of preventing the "ground loss" of effective grounding system, limiting the short circuit current of transformer neutral point and reducing the damage of neutral point overvoltage to the insulation of the system, and the protection of neutral point overvoltage. It is no longer necessary to install clearance, which can effectively avoid the hidden trouble caused by clearance to the system. At present, the neutral point of domestic 500kV auto-transformer has been tested by small reactance grounding mode, and the effect is good. However, the neutral point of 110kV and 220kV transformer is still in the stage of perfect theory and field test, while the neutral point of 110kV and 220kV transformer is running through small reactance grounding mode. It is necessary to do further research on this problem. This paper mainly studies the change of transformer and system zero-sequence impedance after the system is connected with small reactance, and analyzes its short-circuit current to neutral point. The influence of the zero sequence impedance of the system and the insulation level of the transformer neutral point; The small reactance device is designed and suggested that the value range of the small reactance is 1 / 3 of the zero sequence impedance of the transformer. This paper also optimizes and improves the partial grounding method used in transformer neutral point at present. Through the analysis of the causes of many accidents, it is found that the setting of the protection parameters at the neutral point should be based on the actual over-voltage at the neutral point of the transformer. However, the discharge voltage of standard lightning wave and power frequency voltage wave is the reference of lightning arrestor and clearance setting at present, which leads to the unreliable protection of neutral point insulation. After considering the influence factors of substation operation, this paper uses EMTP simulation software to simulate the waveform of lightning overvoltage and single-phase-to-earth power frequency overvoltage caused by neutral point. Finally, the parameters of clearance and arrester are adjusted. However, the gap of rod used at present still has the shortcomings of wrong distance adjustment, poor concentric degree and high dispersion of discharge. Under the action of arc, the electrode is ablative and the distance of rod gap is changed, which makes the use frequency of the gap lower. This paper also puts forward some suggestions for the improvement of gap.
【学位授予单位】：山西大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM41

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