- 學位論文
以長距離電纜併聯的大型電廠接地系統之接地故障特性研究
Ground Fault Characteristics of Grounding System in the Large Plants with Long Cable Interconnections
摘要
本論文探討多機組的大型電廠以長距離電纜併聯時，其接地系統的穩態接地故障特性，其中考慮機組主變壓器中性點接地與否及電纜充電電容的影響，所探討的接地故障特性包括機組地網及開關場地網之地電位昇、接觸電壓、步間電壓、地表面電位、磁場及導體電流之分佈，以及電纜遮蔽層導體及互連導體(輔助接地線)等之電流及電壓分佈，並藉此評估對人員、設備及電纜之影響，文中將先建構單相接地故障之相序網路模型以分析最嚴重的故障電流分佈，然後建構接地系統的電路模型，其中將同時考慮機組地網、開關場地網及其互連的電纜遮蔽層導體及互連導體，其中電纜遮蔽層導體之交錯換位問題將在被考慮以建構其等效階梯電路模型連接在兩地網之間供分析電流分佈，及注入地網之電流，一電磁分析軟體”CDEGS”被應用分析所有的分佈值，研究結果顯示，主變壓器的中性點接地與否及電纜遮蔽導體與互連導體對整體的接地系統故障特性影響最大，電纜充電電容對穩態的接地故障特性影響極小。主變壓器中性點接地將增加故障電流亦增加地網的危險性，本文將評估這些危險性以供參考。
並列摘要
This work regards the characteristics of grounding system during steady state grounding fault on the multi-unit large plant with long cable connection to system. The ground potential rises (GPR), touch voltages, step voltages and electromagnetic fields caused by grounding fault are first analyzed by the software “CDEGS”, and the current and voltage distributions on the shielding conductors of cable are studied. In the thesis, the worst fault current is analyzed by sequence network where the ground grids of generator unit and switch yard and cable shielding conductors are considered. The study results had shown that the ground fault current will increase with the number of main transformer with neutral grounded directly. This will increase the hazards in the switch yard ground grid. The effects of capacitances of the cable on steady state ground fault current can be neglected. This study provides useful data for planning the improvement strategies of large plant ground system.