【摘要】：隨著我國用電負荷水平的增加,以及能源區和負荷區的分布嚴重不均,遠距離、大功率、跨區域輸電線路越來越多地出現我國的電力系統中,而直流輸電系統具有經濟性好、運行性能可靠和不存在交流輸電系統的穩定性問題等特點,非常適合進行遠距離和大功率輸電。研究直流輸電系統過電壓,確定直流輸電線路的絕緣水平,對確定我國的能源安全,保障我國經濟的發展具有重大的意義。直流線路接地故障是直流線路上最常見的故障,而且會產生線路上最嚴重的過電壓,因此對直流輸電系統單極接地過電壓進行計算研究是有必要的。 本文先對直流輸電系統單極接地過電壓的原理進行理論分析,找出影響過電壓的相關因素。再對直流輸電系統進行電路等效處理,根據等效電路圖列出各點電壓和電流的狀態微分方程,用改進歐拉法對典型直流輸電系統單極接地過電壓進行計算,結果表明故障點位于線路中點時會在非故障極產生最高的過電壓；線路越短,線路上過電壓水平越高；故障接地電阻能降低故障時引起的電壓波的暫態分量,故障接地電阻越大,過電壓幅值越小。 為對直流輸電系統單極接地過電壓進行精確計算和詳細分析,選用PSCAD軟件,根據云廣特高壓直流輸電系統的實際參數,建立了特高壓直流輸電系統的仿真模型,詳細計算了直流濾波器、平波電抗器,線路長度,故障接地電阻、負荷水平、大地電阻率和故障位置等因素對直流輸電系統單極過電壓的影響,以及故障時換流站內各設備的過電壓。計算結果表明最大過電壓出現在故障點為線路中點時,直流濾波器、負荷水平和大地電阻率對過電壓有一定影響,負荷水平越高,過電壓越大,大地電阻率越高,過電壓越低,但是影響不大,平波電抗器電感值和配置方式對過電壓有較大影響,電感值越大,過電壓越小,全部裝設在極母線性上時要比分別裝在極母線和中性母線上時的過電壓要小,線路長度和故障接地電阻對過電壓的影響與前面用改進歐拉法計算得到的結論一致,當線路長度為800km時線路上最大的過電壓達到1.7pu,值得引起重視,發生接地故障時會在換流站設備上產生一定的過電壓,直流濾波器因更靠近線路端,所以受到的影響較大,當故障點位于換流站附近時,會在其電感上引起較大的過電壓,對其絕緣產生威脅,值得引起注意。對于限制過電壓的措施,可選擇在線路中點處安裝避雷器,能有效限制過電壓。
[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.
【學位授予單位】：廣西大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM721.1

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