The Study of An Indirect Cooling System for High-Voltage Electrical Cables In Underground Tunnels

對於地下電力纜線來說，當纜線在輸送電流之時，由於纜線本身的電阻的緣故，局部能量會轉變為熱能形式散失，所以冷卻系統的設計，便成了解決地下電纜洞道散熱最主要的問題。 本實驗研究計畫將透過調查與統計的方式對各種冷卻系統分析比較，並依據過去之文獻，進一步推估未來可能之需求。實驗內容採用洞道內水管間接冷卻的方式，並依據相似定律來針對實際的洞道尺寸建立模型以進行洞道模擬實驗，沿著洞道入口對不同的洞道剖面量測各部位之洞道溫度、冰水管溫度及電纜導體溫度等地下洞道工程設計重要參數的變因加以探討，最後找出設計條件的參考數據。 結果顯示洞道內的溫度會隨著離洞道入口的距離增加而上升，並在入口處的上升幅度最為明顯，代表冰水管前段帶走的熱量較多，隨著冰水管溫度的上升，帶走的熱量便漸漸減少。至於單一剖面的溫度變化則由加熱器位置往上遞減，到洞道上方時受到冰水管附近的冷空氣影響，溫度沿著半圓壁面往下遞減，至洞道半圓壁面最低點溫度最低。冰水流量與洞道溫度有直接的影響，流量越慢，洞道內的溫度越低；冰水管數對洞道整體溫度的高低雖無明顯影響，但管數越多，洞道前後的溫度變化較為平緩，表示系統的熱傳效果較為平均。As far as underground high-voltage electrical cables are concerned, when the cables transmit electric current, a part of electric energy will transform into heat and then dissolve due to electric resistance from the cables themselves. Therefore, designs of cooling systems are the main concern when we try to solve the problem of heat dissipation in underground tunnels where high-voltage electrical cables are installed. In this research we estimate further possible needs based on preceding literatures regarding several such cooling systems. An experimental apparatus is built to study the performance of an indirect cooling system which cooling water tubes are placed through an insulated tunnel. The modeled tunnel that we engage in the simulated tunnel experiment is set up according to similarity laws. At different sections of the tunnel, tests are conducted to measure temperatures of the tunnel, the cooling water tubes, and the electrical cable. The variables are analyzed and studied and references may then be obtained for an optimal design of an underground high-voltage electrical cable tunnel. The result shows that the temperature in the tunnel rises in accordance with the increasing distance from the tunnel entrance. At the entrance of the tunnel, the rising degree of the tunnel’s temperature is the most significant. It indicates that the cooling water tubes in the front section of the tunnel take away heat more. The higher the cooling water tubes’ temperature get, the less heat they take away. As for temperature variation of a single section, the temperature drops compliant with the ascending position away from the heater. At the top part of the tunnel, affected by cold air close to the cooling water tubes, the temperature gets lower and lower around the semicircular wall of the tunnel. The temperature gradually drops to the lowest at the lowest point of the semicircular wall of the tunnel. Water-flow exerts a direct impact on the tunnel’s temperature. The slower the water-flow is, the lower the tunnel’s temperature gets. Though the number of cooling water tubes shows insignificant impact on tunnel’s temperature variation, the more the cooling water tubes are, the smoother the temperature distribution is in the front and rear sections of the tunnel. This indicates the heat transform of the cooling system is more even.目錄 內容 頁次 中文摘要....................................................................................I 英文摘要...................................................................................II 目錄..........................................................................................IV 表目錄....................................................................................VII 圖目錄...................................................................................VIII 符號說明..................................................................................X 第一章 緒論..........................................................................1 1-1 地下電纜洞道冷卻系統發展簡介................................1 1-2 研究動機........................................................................2 1-3 研究目的........................................................................5 第二章 文獻回顧.................................................................6 2-1 地下電纜洞道..................................................................6 2-2 含線性熱源之封閉區間................................................8 第三章 實驗設備與方法..................................................11 3-1洞道主體.............................................................................11 3-2冰水循環系統.....................................................................12 3-2-1 冰水主機.................................................................12 3-2-2 蓄水槽.....................................................................12 3-2-3 循環泵.....................................................................12 3-2-4 分流管.....................................................................13 3-2-5 冰水管.....................................................................13 3-3熱源裝置.............................................................................14 3-4溫度、流量及壓力量測裝置.............................................14 3-5電路系統與其他裝置.........................................................16 3-6 實驗方法與流程................................................................16 3-6-1 實驗方法.....................................................................16 3-6-2 實驗流程.....................................................................17 3-7 實驗參數設定....................................................................17 第四章 結果與討論...........................................................20 4-1 不同流量對洞道內溫度之影響....................................20 4-1-1 流量8LPM時洞道內溫度變化............................20 4-1-2 流量12LPM時洞道內溫度變化..........................22 4-1-3 流量16LPM時洞道內溫度變化...........................23 4-1-4 相同管數不同流量之綜合比較.............................24 4-2 不同管數對洞道內溫度之影響....................................24 4-3 無因次溫度....................................................................25 4-3-1 空氣與冰水管間無因次溫度變化........................25 4-3-2 空氣與加熱器間無因次溫度變化........................26 4-4 洞道內之Nu數.............................................................27 第五章 結論與建議.............................................................30 5-1 結論................................................................................30 5-2 建議................................................................................31 參考文獻.................................................................................33 附表..........................................................................................35 附圖..........................................................................................45 附錄A 溫度效正................................................................91 附錄B 誤差分析................................................................93 附錄C 其他相關圖表.......................................................9