油浸式變壓器藉淺層溫能散熱之性能研究

Abstract

隨著科技文明的發展，能源議題逐漸受到重視，其中以電能的使用最為廣泛。藉由變壓器使得電力在傳輸的過程中，得以提高傳輸能力、並減少電力損失，但仍有一部分的電力在變壓器的繞組及鐵心轉換成熱能，造成變壓器的升溫，縮短變壓器的壽命、減少變壓器容量。 目前降溫的方法多利用油泵、風機、水冷卻器等，有著耗能、噪音、維修困難等問題，隨著再生能源的興起，淺層溫能之應用被視為能降溫且節能的有效方法，並利用地埋管熱交換器攫取淺層溫能。因此，本研究將針對油浸式變壓器結合淺層溫能冷卻系統做測試，瞭解其冷卻性能。 因變壓器的升溫，造成內部絕緣油產生自然對流，而地埋管熱交換器則以水溶液作為工作流體，流經散熱設備將熱能帶入地埋管與土壤進行熱交換。除了比較油浸自冷（空氣中自然冷卻）與油浸水冷（藉淺層溫能冷卻）之差異，也測試了在不同操作條件下的冷卻情形：改變(1)水路流向，(2)變壓器負載、(3)水路流率等，並以實驗和數學理論模式相互結合。結果顯示以淺層溫能做為變壓器的散熱系統，能夠得到有效的降溫，平均油溫約下降30~40 oC，水路流向對於高溫處的降溫能力也不同，且水流率越快，淺層溫能冷卻容量則越大。而理論與實驗結果也有良好的一致性，可作為選擇變壓器容量之參考，提供未來後續研究之基礎。

With the development of civilization and technology, increasing attention has been given to energy issues, of which the use of electricity is among the most widely discussed. By the use of transformers, transmission capacity can be improved to reduce power loss during the transmission process. Still, some portion of the power is converted into heat in the transformer windings and core, causing temperature increase of the transformer, shortening the life span of the transformer, and reducing the transformer capacity. Current cooling methods include the use of pumps, fans, water coolers, etc. However, they come with problems like high power consumption, noise, and maintenance difficulties. Thus, the application of shallow geothermal energy is considered to be an energy efficient cooling method. Moreover, the energy itself can be captured using the borehole heat exchanger. This study focuses on the test results of the oil-immersed transformer cooling system combined with shallow geothermal energy in order to understand its cooling performance. The temperature rise of the transformer causes internal insulating oil to circulate by natural convection. With water as working fluid, borehole heat exchanger brings the heat from the cooling equipment into the borehole and finally conducts heat transfer with the soil. Besides the comparison between ONAN Cooling (air cooling) and ONWF Cooling (shallow geothermal energy cooling), we tested the cooling system under different operating conditions. We manipulated (1) the direction of water flow, (2) load of the transformer, and (3) the water flow rate, and matched the results of the experiments and the mathematical theoretical model. The results showed that the cooling system with shallow geothermal energy effectively cooled down the transformer, with a drop in average oil temperature of about 30~40oC. The cooling performance also varied for different directions of water flow to cool down high temperatures. Moreover, the higher the water flow rate, the greater the cooling capacity. The theory and results of the experiment are in good consistency. Thus, this study may be used as a reference for selecting proper transformer capacity as well as providing a basis for follow-up studies.