A fundamental approach to transformer thermal modeling. I. Theory and equivalent circuit

Abstract

A simple equivalent circuit to represent the thermal heat flow equations for power transformers is presented. Key features are the use of a current source analogy to represent heat input due to losses, and a nonlinear resistor analogy to represent the effect of air or oil cooling convection currents. An interesting historical note concerns the fact that the foregoing effect was first quantified in 1817. It is shown that the idea of "exponential response" is not the best way to think of the dynamics of the situation. It is also shown that one can consider ambient temperature to be a variable input to the system, and that it is properly represented as an ideal voltage source. Physical experimental verification, on an in-service 250 MVA transformer, is described in a companion paper.

Numerical modelling of natural convection of oil inside distribution transformers

“…The number of cells in the Slice model is of the order of 1.25·10 6 . In the Complete model the cell requirement is considerably higher and a number of 4.5·10 6 elements has been considered.…”

“…Looking for a more comprehensive thermal characterization, several authors have studied the performance of transformers by means of simplified equivalent thermal circuits using different approaches [4][5][6][7][8][9]. These models are based on a short number of characteristic temperatures inside the transformer and they rely on some coefficients whose values have to be determined by means of experimentation for each new design.…”

Comparasion between Oil Immersed and SF6 Gas Power Transformers Ratings

“…Figure 1. Thermal over all circuit models where: q tot is the total losses; q heat generated in the winding; R ambient temperature; θ hs is the hot spot temperature; θ R th-hs-oil is the non linear winding to oil thermal resistance; C capacitance and Cth -oil is the oil load and load transformer losses are represented by two ideal heat sources [19], [20].…”

“…The final thermal over all model for oil based on the thermal-electrical analogy and heat transfer theory [17], [18], [19]. Figure 1.…”

Distribution transformer lifetime analysis in the presence of demand response and rooftop PV integration

“…In order to achieve better performance for transformer investment, a correct utilisation of transformer considering loading, ambient temperature, and thermal characteristics is essential. To this aim, a prediction model is vital to estimate the winding hot-spot temperature (HST) and top-oil temperature [17]. Moreover, the detail methodologies to calculate the HST is presented in The Institute of Electrical and Electronics Engineers Standard C57.91-1995 [18] and The International Electrotechnical Commission standard 60076-7 [19].…”