特高压直流输电系统单极接地过电压的研究

发布时间：2018-10-29 20:59

【摘要】：随着我国用电负荷水平的增加,以及能源区和负荷区的分布严重不均,远距离、大功率、跨区域输电线路越来越多地出现我国的电力系统中,而直流输电系统具有经济性好、运行性能可靠和不存在交流输电系统的稳定性问题等特点,非常适合进行远距离和大功率输电。研究直流输电系统过电压,确定直流输电线路的绝缘水平,对确定我国的能源安全,保障我国经济的发展具有重大的意义。直流线路接地故障是直流线路上最常见的故障,而且会产生线路上最严重的过电压,因此对直流输电系统单极接地过电压进行计算研究是有必要的。本文先对直流输电系统单极接地过电压的原理进行理论分析,找出影响过电压的相关因素。再对直流输电系统进行电路等效处理,根据等效电路图列出各点电压和电流的状态微分方程,用改进欧拉法对典型直流输电系统单极接地过电压进行计算,结果表明故障点位于线路中点时会在非故障极产生最高的过电压；线路越短,线路上过电压水平越高；故障接地电阻能降低故障时引起的电压波的暂态分量,故障接地电阻越大,过电压幅值越小。为对直流输电系统单极接地过电压进行精确计算和详细分析,选用PSCAD软件,根据云广特高压直流输电系统的实际参数,建立了特高压直流输电系统的仿真模型,详细计算了直流滤波器、平波电抗器,线路长度,故障接地电阻、负荷水平、大地电阻率和故障位置等因素对直流输电系统单极过电压的影响,以及故障时换流站内各设备的过电压。计算结果表明最大过电压出现在故障点为线路中点时,直流滤波器、负荷水平和大地电阻率对过电压有一定影响,负荷水平越高,过电压越大,大地电阻率越高,过电压越低,但是影响不大,平波电抗器电感值和配置方式对过电压有较大影响,电感值越大,过电压越小,全部装设在极母线性上时要比分别装在极母线和中性母线上时的过电压要小,线路长度和故障接地电阻对过电压的影响与前面用改进欧拉法计算得到的结论一致,当线路长度为800km时线路上最大的过电压达到1.7pu,值得引起重视,发生接地故障时会在换流站设备上产生一定的过电压,直流滤波器因更靠近线路端,所以受到的影响较大,当故障点位于换流站附近时,会在其电感上引起较大的过电压,对其绝缘产生威胁,值得引起注意。对于限制过电压的措施,可选择在线路中点处安装避雷器,能有效限制过电压。
[Abstract]:With the increase of power load level in our country, and the distribution of energy and load areas is seriously uneven, long-distance, high-power, cross-regional transmission lines more and more appear in the power system of our country, but the direct current transmission system has good economy. It is very suitable for long distance and high power transmission due to its reliable operation performance and the absence of stability problems of AC transmission systems. It is of great significance to study the overvoltage of HVDC transmission system and determine the insulation level of HVDC transmission lines to determine the energy security of our country and ensure the economic development of our country. DC grounding fault is the most common fault on DC line, and it will produce the most serious overvoltage on the line. Therefore, it is necessary to calculate the unipolar grounding overvoltage of HVDC transmission system. In this paper, the principle of unipole grounding overvoltage in HVDC system is analyzed theoretically, and the related factors affecting overvoltage are found out. Then the equivalent circuit of HVDC system is treated, according to the equivalent circuit diagram, the state differential equations of voltage and current at each point are listed, and the single-pole grounding overvoltage of typical HVDC transmission system is calculated by improved Euler method. The results show that when the fault point is at the midpoint of the line, the highest overvoltage will be generated at the non-fault pole. The shorter the line is, the higher the over-voltage level on the line is, and the fault grounding resistance can reduce the transient component of the voltage wave caused by the fault, the larger the fault grounding resistance, the smaller the overvoltage amplitude. In order to accurately calculate and analyze the unipolar grounding overvoltage of HVDC system, the simulation model of UHV HVDC system is established according to the actual parameters of Yunguang UHVDC transmission system by using PSCAD software. The effects of DC filter, flat-wave reactor, line length, fault grounding resistance, load level, earth resistivity and fault location on unipolar overvoltage of HVDC transmission system are calculated in detail. And the overvoltage of the equipment in the converter station when the fault. The calculation results show that the DC filter, load level and earth resistivity have a certain influence on the overvoltage when the maximum overvoltage occurs at the fault point. The higher the load level, the greater the overvoltage, the higher the earth resistivity and the lower the overvoltage. However, the influence of the inductance and configuration of the flat-wave reactor on the overvoltage is great. The larger the inductance, the smaller the overvoltage, and the smaller the overvoltage is when all of them are installed on the pole busbar and the neutral bus, respectively. The effect of line length and fault grounding resistance on overvoltage is consistent with the results obtained by the improved Euler method. When the line length is 800km, the maximum overvoltage on the line is 1.7 pu. it is worthy of attention. When grounding fault occurs, a certain overvoltage will be generated on the converter station equipment. Because the DC filter is closer to the line end, it will be greatly affected. When the fault point is near the converter station, it will cause a larger overvoltage on its inductance. The threat to its insulation deserves attention. For the measures to limit the overvoltage, the lightning arrester can be installed at the midpoint of the line, which can effectively limit the overvoltage.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

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