Reduction of Stray Losses in Flange–Bolt Regions of Large Power Transformer Tanks

In large power transformers, the presence of stray currents in the structural elements near the high current bushings can be considerable, and this leads to hot spots. This work presents a practical analysis of overheating in the bolts that join the tank and the cover, which are near the high current bushings of the transformer. Overheating results are analyzed and discussed for the case of a 420-MVA transformer. The hot spots in the flange-bolt regions are discovered by thermal maps that are obtained during power transformer operation as a part of a preventive maintenance program. In this paper, we use copper links to ensure the connection of both the cover and tank body, significantly reducing the overheating of the flange-bolt region. The copper link solution has been validated by measurements. We have used calibrated measurement instruments in all the experiments. Moreover, a 3-D finite-element analysis of the geometry of interest has been used to verify the copper link solution.

[1]  Hee-Je Kim,et al.  Analysis and Design of a Multioutput Converter Using Asymmetrical PWM Half-Bridge Flyback Converter Employing a Parallel–Series Transformer , 2013, IEEE Transactions on Industrial Electronics.

[2]  Giampaolo Buticchi,et al.  Detection Method of the DC Bias in Distribution Power Transformers , 2013, IEEE Transactions on Industrial Electronics.

[3]  Martin Ordonez,et al.  Applying Response Surface Methodology to Small Planar Transformer Winding Design , 2013, IEEE Transactions on Industrial Electronics.

[4]  Antonios G. Kladas,et al.  Analysis of Transformers Working Under Heavily Saturated Conditions in Grid-Connected Renewable-Energy Systems , 2012, IEEE Transactions on Industrial Electronics.

[5]  Wuhua Li,et al.  General Derivation Law of Nonisolated High-Step-Up Interleaved Converters With Built-In Transformer , 2012, IEEE Transactions on Industrial Electronics.

[6]  Janusz Turowski,et al.  Non linear Heating Hazard Assessment on Transformer Covers and Tank Walls , 2012 .

[7]  Antonios G. Kladas,et al.  Harmonic Impact on Distribution Transformer No-Load Loss , 2010, IEEE Transactions on Industrial Electronics.

[8]  M. A. Arjona,et al.  Thermal-fluid transient two-dimensional characteristic-based-split finite-element model of a distribution transformer , 2012 .

[9]  Tang Renyuan,et al.  New preventive measures against stray field of heavy current carrying conductors , 1996 .

[10]  Janusz Turowski,et al.  3D heating hazard assessment on transformer covers. Arrangement decisions , 2012 .

[11]  Rafael Escarela-Perez,et al.  Diseño y construcción de un sistema de lavado en vivo para los aisladores de transformadores , 2012 .

[12]  Ahmed M. Massoud,et al.  Multiple-Module High-Gain High-Voltage DC–DC Transformers for Offshore Wind Energy Systems , 2011, IEEE Transactions on Industrial Electronics.

[13]  Tang Renyuan,et al.  Solutions of three-dimensional multiply connected and open boundary problems by BEM in three-phase combination transformers , 1992 .

[14]  Janusz Turowski,et al.  3-D methodology for the heating hazard assessment on transformer covers , 2010, The XIX International Conference on Electrical Machines - ICEM 2010.

[15]  Antonios G. Kladas,et al.  Power Transformer Economic Evaluation in Decentralized Electricity Markets , 2012, IEEE Transactions on Industrial Electronics.

[16]  Pavlos S. Georgilakis.  Spotlight on Modern Transformer Design , 2009 .

[17]  Pavlos S. Georgilakis,et al.  Techno-economic Evaluation of Reduction of Low-voltage Bushings Diameter in Single-phase Distribution Transformers , 2011 .

[18]  Tang Renyuan,et al.  Computation of eddy current losses by heavy current leads and windings in large transformers using IEM coupled with improved R- Psi method , 1990 .

[19]  H. W. Kerr,et al.  Large power transformers , 1964 .

[20]  Josep M. Guerrero,et al.  Voltage-Based Control of a Smart Transformer in a Microgrid , 2013, IEEE Transactions on Industrial Electronics.

[21]  J. Turowski,et al.  Evaluation of eddy current losses in the cover plates of distribution transformers , 2004 .

[22]  Michael A. E. Andersen,et al.  Optimal Design and Tradeoff Analysis of Planar Transformer in High-Power DC–DC Converters , 2012, IEEE Transactions on Industrial Electronics.

[23]  R. Escarela-Perez,et al.  Experimental validation of a new methodology to reduce hot spots on the screws of power transformer tanks , 2012, 2012 XXth International Conference on Electrical Machines.

[24]  S. A. Khaparde,et al.  Transformer Engineering: Design and Practice , 2004 .

[25]  M. V. Ferreira da Luz,et al.  3D calculation and modeling of eddy current losses in a large power transformer , 2012, 2012 XXth International Conference on Electrical Machines.

[26]  C. Bengtsson,et al.  Status and trends in transformer monitoring , 1996 .

[27]  C. P. McShane,et al.  Relative properties of the new combustion-resist vegetable-oil-based dielectric coolants for distribution and power transformers , 2001 .