A Thermal Equivalent Circuit for Thermal Analysis of Power Transformers under Harmonic Loads
Subject Areas : electrical and computer engineering
m.
mikhak
1
B.
Rezaeealam
2
m.
jafarboland
3
v.
ebrahimian
4
m.
asgari
5
Keywords: Oil power transformernon-sinusoidal currentsthermal equivalent circuitfinite element method,
Abstract :
The majority of the power transformers failures are caused by the thermal stresses under abnormal operating conditions, such as harmonic loads. Therefore, it is of great interest to determine the temperature distribution inside the power transformers. In this paper, a new thermal equivalent circuit is presented by which the temperature in different regions of the transformer is estimated under harmonic loads. Also, the three-dimensional Finite Element (FE) Model of the power transformer is developed to calculate the power losses in each part of the transformer that are considered as the heat sources in the proposed equivalent circuit. The computed hotspot and average oil temperatures are compared with those obtained from IEEE Std C57.91 method, thereby the accuracy of the proposed method for calculating the temperature rise due to harmonic loads, is investigated. Finally, derating of the power transformer is discussed under harmonic loads.
[1] M. Sharifian and J. Faiz, "Derating of a distribution transformer for non‐linear loads," European Trans. on Electrical Power, vol. 16, no. 2, pp. 189-203, Nov. 2006.
[2] ANSI/IEEE Std C57.110, IEEE Recommended Practice for Establishing Transformer Capability When Supplying Non-sinusoidal Load Currents, 1986.
[3] P. Staats, et al., "A procedure for derating a substation transformer in the presence of widespread electric vehicle battery charging," IEEE Trans. on Power Delivery, vol. 12, no. 4, pp. 1562-1568, Oct. 1997.
[4] S. Taheri, et al., "Modeling and simulation of transformer loading capability and hot spot temperature under harmonic conditions," Electric Power Systems Research, vol. 86, no. 1, pp. 68-75, May 2012.
[5] B. Das and Z. R. Radakovic, "Is transformer kVA derating always required under harmonics? A manufacturer's perspective," IEEE Trans. on Power Delivery, vol. 33, no. 6, pp. 2693-2699, Mar. 2018.
[6] I IEEE Std C57.110-2008, IEEE Recommended Practice for Establishing Liquid-Filled and Dry-Type Power and Distribution Transformer Capability When Supplying Nonsinusoidal Load Currents, pp. 1-52, 2008.
[7] M. Ghazizadeh, J. Faiz, and H. Oraee, "Derating of distribution transformers under non-linear loads using a combined analytical-finite elements approach," IET Electric Power Applications, vol. 10, no. 8, pp. 779-787, Sept. 2016.
[8] G. Swift, T. S. Molinski, and W. Lehn, "A fundamental approach to transformer thermal modeling: I- Theory and equivalent circuit," IEEE Trans. on Power Delivery, vol. 16, no. 2, pp. 171-175, Apr. 2001.
[9] D. Susa, M. Lehtonen, and H. Nordman, "Dynamic thermal modelling of power transformers," IEEE Trans. on Power Delivery, vol. 20, no. 1, pp. 197-204, Feb. 2005.
[10] D. Susa and M. Lehtonen, "Dynamic thermal modeling of power transformers: further development-part i," IEEE Trans. on Power Delivery, vol. 21, no. 4, pp. 1961-1970, Oct. 2006.
[11] D. Susa and H. Nordman, "A simple model for calculating transformer hot-spot temperature," IEEE Trans. on Power Delivery, vol. 24, no. 3, pp. 1257-1265, Jun. 2009.
[12] L. Zhu, et al., "An improved dynamic thermal circuit model for transformers and its application to evaluate capacity increase," Electric Power Components and Systems, vol. 45, no. 13, pp. 1440-1449, Aug. 2017.
[13] I. Iskender and A. Mamizadeh, "An improved nonlinear thermal model for MV/LV prefabricated oil-immersed power transformer substations," Electrical Engineering, vol. 93, no. 1, pp. 9-22, Mar. 2011.
[14] A. Najafi and I. Iskender, "An improved thermal model for distribution transformer under unbalanced voltage conditions," International J. of Thermal Sciences, vol. 104, no. 1, pp. 373-385, Jun. 2016.
[15] B. Szabados, et al., "A new approach to determine eddy current losses in the tank walls of a power transformer," IEEE Trans. on Power Delivery, vol. 2, no. 3, pp. 810-816, Jul. 1987.
[16] Z. Valkovic, "Calculation of the losses in three-phase transformer tanks," IEE Proc. C: Generation, Transmission and Distribution), vol. 1, pp. 20-25, Jan. 1980.
[17] N. Takahashi, T. Sakura, and Z. Cheng, "Nonlinear analysis of eddy current and hysteresis losses of 3-D stray field loss model (problem 21)," IEEE Trans. on Magnetics, vol. 37, no. 5, pp. 3672-3675, Sept. 2001.
[18] H. V. Sande, et al., "An effective reluctivity model for nonlinear and anisotropic materials in time-harmonic finite element computations," IEEE Trans. on Magnetics, vol. 41, no. 5, pp. 1508-1511, May 2005.
[19] I. R. Ciric and F. I. Hantila, "An efficient harmonic method for solving nonlinear time-periodic eddy-current problems," IEEE Trans. on Magnetics, vol. 43, no. 4, pp. 1185-1188, Mar. 2007.
[20] G. Paoli, O. Biro, and G. Buchgraber, "Complex representation in nonlinear time harmonic eddy current problems," IEEE Trans. on Magnetics, vol. 34, no. 5, pp. 2625-2628, Sept. 1998.
[21] J. Faiz, B. M. Ebrahimi, and M. Ghofrani, "Mixed derating of distribution transformers under unbalanced supply voltage and nonlinear load conditions using TSFEM," IEEE Trans. on Power Delivery, vol. 25, no. 2, pp. 780-789, Jan. 2010.
[22] J. Olivares, et al., "2D finite-element determination of tank wall losses in pad-mounted transformers," Electric Power Systems Research, vol. 71, no. 2, pp. 179-185, Jan. 2004.
[23] X. Liu, Y. Yang, and F. Yang, "Numerical research on the losses characteristic and hot-spot temperature of laminated core joints in transformer," Applied Thermal Engineering, vol. 110, no. 5, pp. 49-61, Jan?. 2017.
[24] P. Picher, et al., "Optimization of transformer overload using advanced thermal modelling," in Proc. CIGRE Conf., Article A2-305, Paris, France, 29-30 Jan. 2010.
[25] D. Susa and M. Lehtonen, "Dynamic thermal modeling of power transformers: further development-part ii," IEEE Trans. on Power Delivery, vol. 21, no. 4, pp. 1971-1980, Oct. 2006.
[26] L. Wang, et al., "Improved dynamic thermal model with pre-physical modelling for transformers in ONAN cooling mode," IEEE Trans. on Power Delivery, vol. 34, no. 4, pp. 1442-1450, March. 2019.
[27] L. Zhou, et al., "Oil exponent thermal modelling for traction transformer under multiple overloads," IET Generation, Transmission & Distribution, vol. 12, no. 22, pp. 5982-5989, Oct. 2018.
[28] IEEE Std. C57.91-2011, IEEE Guide for Loading Mineral-Oil-Immersed Transformers and Step-Voltage Regulators, (Revision of pp. 1-123, 2012.
[29] J. Zhang and X. Li, "Oil cooling for disk-type transformer windings-part 1: theory and model development," IEEE Trans. on Power Delivery, vol. 21, no. 3, pp. 1318-1325, Jun. 2006.