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Research Papers

Performance Study of an Oil-Immersed Power Transformer With Shallow Geothermal Cooling

[+] Author and Article Information
Gerd Schmid

Department of Mechanical Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan
e-mail: d99522042@ntu.edu.tw

Chien-Yeh Hsu

Department of Mechanical Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan
e-mail: d00522028@ntu.edu.tw

Yu-Ting Chen

Department of Mechanical Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan
e-mail: b99203059@ntu.edu.tw

Tai-Her Yang

Giant Lion Know-How Co., Ltd.,
P.O. Box: 108-276,
Taipei 10692, Taiwan
e-mail: giantleo@ms24.hinet.net

Sih-Li Chen

Department of Mechanical Engineering,
National Taiwan University,
No. 1, Sec. 4, Roosevelt Road,
Taipei 10617, Taiwan
e-mail: slchen01@ntu.edu.tw

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received July 28, 2015; final manuscript received October 19, 2015; published online November 17, 2015. Assoc. Editor: Pedro Mago.

J. Thermal Sci. Eng. Appl 8(2), 021004 (Nov 17, 2015) (8 pages) Paper No: TSEA-15-1203; doi: 10.1115/1.4031889 History: Received July 28, 2015; Revised October 19, 2015

This paper investigates the cooling performance of a shallow geothermal energy method in relation to the cooling system of a 75 kVA oil-immersed transformer. A thermal analysis of the complete system is presented and then validated with experimental data. The cooling performance of the shallow geothermal cooling method is indicated by its cooling capacity and average oil temperature. The results of this study show that the average oil temperature can be reduced by nearly 30 °C with the aid of an 8 m deep U-pipe borehole heat exchanger, thereby making it possible to increase the capacity of the transformer. By increasing the water flow rate from 6 L/m to 15 L/m, the average oil temperature could be lowered by 3 °C. In addition, the effects of changing the circulating water flow direction and the activation time of the shallow geothermal cooling system were investigated. The results of the thermal analysis are consistent with the experimental data, with relative errors below 8%. The results of the study confirm that a larger temperature difference between the cooling water and the transformer oil at the inlet of the heat exchanger can increase the overall heat transfer rate and enhance the cooling performance of the shallow geothermal cooling system.

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Figures

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Fig. 1

Control volume of oil-immersed transformer and cooling equipment

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Fig. 2

Schematic figure of U-tube borehole heat exchangers

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Fig. 3

Oil-immersed transformer and shallow geothermal cooling system

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Fig. 4

Photographic view of experimental setup with main components

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Fig. 5

Thermal conditions inside the borehole

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Fig. 6

Oil-temperature profile of cooling transformer by active and passive methods

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Fig. 7

Temperature profile when cooling system is activated all the time

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Fig. 8

Temperature profile when cooling system is only activated at full-load condition

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Fig. 9

Temperature profiles of oil at different flow rates of circulating water

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