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.

References

References
1.
2.
Harlow
,
J. H.
,
2012
, Electric Power Transformer Engineering (The Electric Power Engineering Series 9),
CRC Press
,
Boca Raton, FL
, Chap. 2.
3.
Kim
,
M. G.
,
Cho
,
S. M.
, and
Kim
,
J. K.
,
2012
, “
Prediction and Evaluation of the Cooling Performance of Radiators Used in Oil-Filled Power Transformer Applications With Non-Direct and Direct-Oil-Forced Flow
,”
Exp. Therm. Fluid Sci.
,
44
, pp.
392
397
.
4.
Amoiralis
,
E. I.
,
Tsili
,
M. A.
,
Kladas
,
A. G.
, and
Souflaris
,
A. T.
,
2012
, “
Distribution Transformer Cooling System Improvement by Innovative Tank Panel Geometries
,”
IEEE Trans. Dielectr. Electr. Insul.
,
19
(
3
), pp.
1021
1028
.
5.
Taghikhani
,
M. A.
, and
Gholami
,
A.
,
2009
, “
Prediction of Hottest Spot Temperature in Power Transformer Windings With Non-Directed and Directed Oil-Forced Cooling
,”
Int. J. Electr. Power
,
31
(
7–8
), pp.
356
364
.
6.
Gouda
,
O. E.
,
Amer
,
G. M.
, and
Salem
,
W. A. A.
,
2012
, “
Predicting Transformer Temperature Rise and Loss of Life in the Presence of Harmonic Load Currents
,”
Ain Shams Eng. J.
,
3
(
2
), pp.
113
121
.
7.
Smolka
,
J.
,
Ingham
,
D. B.
,
Elliott
,
L.
, and
Nowak
,
A. J.
,
2007
, “
Enhanced Numerical Model of Performance of an Encapsulated Three-Phase Transformer in Laboratory Environment
,”
Appl. Therm. Eng.
,
27
(
1
), pp.
156
166
.
8.
Hosseini
,
R.
,
Nourolahi
,
M.
, and
Gharehpetian
,
G. B.
,
2008
, “
Determination of OD Cooling System Parameters Based on Thermal Modeling of Power Transformer Winding
,”
Simul. Modell. Pract. Theory
,
16
(
6
), pp.
585
596
.
9.
Gastelurrutia
,
J.
,
Ramos
,
J. C.
,
Rivas
,
A.
,
Larraona
,
G. S.
,
Izagirre
,
J.
, and
Rio
,
L. D.
,
2011
, “
Zonal Thermal Model of Distribution Transformer Cooling
,”
Appl. Therm. Eng.
,
31
(
17–18
), pp.
4024
4035
.
10.
Jalaluddin
, and
Miyara
,
A.
,
2012
, “
Thermal Performance Investigation of Several Types of Vertical Ground Heat Exchangers With Different Operation Mode
,”
Appl. Therm. Eng.
,
33–34
, pp.
167
174
.
11.
Esen
,
H.
, and
Inalli
,
M.
,
2009
, “
In-Situ Thermal Response Test for Ground Source Heat Pump System in Elazig, Turkey
,”
Energy Build.
,
41
(
4
), pp.
395
401
.
12.
Raymond
,
J.
,
Therrien
,
R.
, and
Gosselin
,
L.
,
2011
, “
Borehole Temperature Evolution During Thermal Response Tests
,”
Geothermics
,
40
(
1
), pp.
69
78
.
13.
Gu
,
Y.
, and
O'Neal
,
D. L.
,
1998
, “
Development of an Equivalent Diameter Expression for Vertical U-Tubes Used in Ground-Coupled Heat Pumps
,”
ASHRAE Trans.
,
104
, pp.
347
355
.
14.
Allan
,
M. L.
,
2000
, “
Materials Characterization of Superplasticized Cement–Sand Grout
,”
Cem. Concr. Res.
,
30
(
6
), pp.
937
942
.
15.
Koohi-Fayegh
,
S.
, and
Rosen
,
M. A.
,
2013
, “
A Review of the Modelling of Thermally Interacting Multiple Boreholes
,”
Sustainability
,
5
(
6
), pp.
2519
2536
.
16.
Lee
,
C.
,
Park
,
M.
,
Nguyen
,
T. B.
,
Sohn
,
B.
,
Choi
,
J. M.
, and
Choi
,
H.
,
2012
, “
Performance Evaluation of Closed-Loop Vertical Ground Heat Exchangers by Conducting In-Situ Thermal Response Tests
,”
Renewable Energy
,
42
, pp.
77
83
.
17.
Laughton
,
M. A.
, and
Warne
,
D. J.
,
2003
,
Electrical Engineer's Reference Book
,
Elsevier Science
,
Oxford
, Chap. 33.
18.
Liang
,
N. W.
,
Lai
,
C. H.
,
Hsu
,
C. Y.
,
Chiang
,
Y. C.
,
Chang
,
C. C.
, and
Chen
,
S. L.
,
2014
, “
A Conformal-Mapping Method for Predicting the Thermal Properties of U-Shaped Borehole Heat-Exchangers
,”
Geothermics
,
50
, pp.
66
75
.
19.
Zeng
,
H. Y.
,
Diao
,
N. R.
, and
Fang
,
Z. H.
,
2003
, “
Heat Transfer Analysis of Boreholes in Vertical Ground Heat Exchangers
,”
Int. J. Heat Mass Transfer
,
46
(
23
), pp.
4467
4481
.
20.
Hellström
,
G.
,
1991
, “
Thermal Analysis of Duct Storage Systems
,” Ph.D. thesis, University of Lund, Lund, Sweden.
21.
Cengel
,
Y. A.
,
2006
,
Heat and Mass Transfer
,
3rd ed.
,
McGraw-Hill
,
New York
, pp.
175
176
, 463–473.
22.
Lee
,
T.-W.
,
2008
,
Thermal and Flow Measurements
,
CRC Press, Taylor and Francis Group
,
New York
, pp.
28
38
.
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