Thermal Overshoot Analysis for Hot-spot Temperature Rise of Transformer

The final goal of the paper is to establish a transient moisture equilibrium model for estimating the moisture in paper of the running oil-immersed transformer. To this end, the presented model for oil-paper insulation is improved according to the insulation structure of oil-immersed transformer. The moisture diffusion process is divided into three steps, i.e., between paper and oil, between support insulation and oil, and in oil. In order to improve the accuracy of the model, the added moisture due to ageing of paper insulation is also taken into account.By (20) in [1], the relation between the moisture in paper and the oil duct near the paper follows:where, C Paper (t) is the transient moisture concentration in paper (%); τ Paper (t) is the equilibrium time constant (h), which is obtained by (25) in [1]; C ss (T(t),C OilDuct (t)) is the equilibrium moisture concentration in paper (%), when the moisture concentration of duct oil (μL/L), C OilDuct (t), and the temperature ( o C), T(t), both remain, and it can be obtained by (9) in [5], as a continuation of authors' previous work, according to which, moisture is distributed between oil and paper stably at arbitrary working temperature as Figure.1 and Figure.2. The coil of transformer are covered by several levels paper, which can be looked upon only one single-sided diffusion paper, with n×l Paper thickness, where l Paper is the thickness of one paper, and n is the number of paper levels, so the equilibrium time constant is expressed:where, A 0 , A 1 , A 2 and A 3 are constants, respectively equal to -7.331×10 -2 , -33.545, 7.9575 and -14.1, according to [1].If the added moisture due to ageing of paper insulation is taken into account, (1) should be changed to:where, v WInPaper (t) is the moisture acreasing rate by ageing of paper insulation. Figure.1 Moisture in oil (ppm ) versus moisture in paper (%) at the arbitrary temperature from 0 o C to 60 o C Figure.2 Moisture in oil (ppm ) versus moisture in paper (%) at the the arbitary temperatrue from 60 o C to 100 o C By substituting equation (2) for the equilibrium time constant, τ Paper (t), into equation (3), the following

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“…where, B is a constant, T ( t ) is the temperature of hot spot, which can be obtained by testing or calculating [10][11][12][13].…”

Section: Moisture Increasing By Ageingmentioning

confidence: 99%

Transient moisture equilibrium in oil-immersed transformer

Zhou

Liu

et al. 2009

2009 IEEE 9th International Conference on the Properties and Applications of Dielectric Materials

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“…However, due to the restrictions of related standards [18] and the consideration of capacity and safety, long‐time heat tests under overload are not allowed. Besides the experimental tests, numerical simulation [19, 20] based on the finite element method or the finite volume method, physical modelling [21–25] based on fluid mechanics, heat transfer theory, and electrical loss are effective means to explore local characteristics and solve specific thermal parameters in the transformer. However, as previously mentioned, the oil exponent is different among different transformers and this inconsistency (heterogeneity) will be amplified under overload.…”

Section: Introductionmentioning

confidence: 99%

Oil exponent thermal modelling for traction transformer under multiple overloads

Zhou

Wang

Tang

et al. 2018

IET Generation, Transmission & Distribution

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“…During service, the oil/paper insulation of traction substation transformers, compared with general power transformers, must withstand stresses caused by non-periodic and short-time load shocks, high-temperature rises, and transient overvoltages, etc. [1][2][3][4]. Such load characteristics of the traction power supply and distribution system lead to a rapid aging of the traction substation transformers and thus result in various defects in their insulation.…”

Section: Introductionmentioning

confidence: 99%

Influences of Traction Load Shock on Artificial Partial Discharge Faults within Traction Transformer—Experimental Test for Pattern Recognition

Gao

et al. 2017

Energies

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Partial discharge (PD) measurement and its pattern recognition are vital to fault diagnosis of transformers, especially to those traction substation transformers undergoing repetitive traction load shocks. This paper presents the primary factors induced by traction load shocks including high total harmonics distortion (THD), transient voltage impulse and high-temperature rise, and their effects on the feature parameters of PD. Experimental tests are conducted on six artificial PD models with these factors introduced one by one. Results reveal that the maximum PD quantity and the PD repetitive rate are favorable to be enlarged when the oil temperature exceeds 80 • C or the THD is higher than 16% with certain orders of harmonic. The decline in PD inception voltage can mainly be attributed to the transient voltage impulse. The variation in central frequency of the fast Fourier transformation (FFT) spectra transformed from ultra-high frequency signals can mainly be attributed to high THD, especially when it exceeds 20%. The temperature rise has no significant influence on the FFT spectra; the transient voltage impulse, however, can result in a central frequency shift of the floating particle discharge. With the rapid development of high-speed railways, the study presented in this paper will be helpful for field PD detection and recognition of traction substation transformers in the future.

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Thermal Overshoot Analysis for Hot-spot Temperature Rise of Transformer

Cited by 23 publications

References 12 publications

Transient moisture equilibrium in oil-immersed transformer

Transient moisture equilibrium in oil-immersed transformer

Oil exponent thermal modelling for traction transformer under multiple overloads

Influences of Traction Load Shock on Artificial Partial Discharge Faults within Traction Transformer—Experimental Test for Pattern Recognition

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