On the determination of characteristic temperatures in power oil transformers during transient states

A priori metrics to select best training dataset of top-oil temperature models of power transformers

“…Consequently, Linear model is not an appropriate model to use in an online monitoring system and will be eliminated from further study on ONAN transformer in this paper. The reason of inappropriateness of Linear model is that Linear model considers oil time constant as a constant value for all conditions but oil time constant is a temperature dependent value [9]. Table III shows the value of indices related to normal plot of standardized training error for ONAN transformer.…”

Variation of Steady-State Thermal Characteristics of Transformers with OFWF Cooling in Service

“…Based on the measuring results, the following are calculated: the power of cooling by natural ambient air free convection (P a ) from Equations (19)-(23); the power of cooling through each of heat exchangers oil/water (P ) using Equation (18); the oil and water mass flow rates from Equations (4) and (5), respectively; the flow rates (q) by simple dividing of the mass flow rates with the density; and overall heat transfer coefficient using Equation (7). The calculation results are shown in Table 2.…”

“…Radaković and A. Popović transfer from oil to an external cooling medium (air or water) is not direct application of heat transfer theory, rather, it is the use of simplified functional dependencies of oil to external cooling medium temperature gradient from transformer load. Such approaches are used in valid international standards [6], previous publications of the authors [4,7], as well as recently published papers [8,9]. The usage of the average heat transfer coefficient is typical in a transformer-designing process to calculate the needed number (area) of cooling surfaces.…”

Smart load management of distribution‐class toroidal transformers using a dynamic thermal model

“…Dynamic thermal models based on the simplified equivalent electrical circuits for oil-immersed highvoltage (HV) transformers have been presented in [17][18][19], and top oil model is illustrated in [19]. Kalic et al [20] suggest the determination of temperature-dependent conductances and constant capacitances for the equivalent thermal circuits of a transformer. Variation of losses and thermal parameters are considered.…”

“…Variation of losses and thermal parameters are considered. However, the assumption of constant specific heat in [20] is not realistic. Analytical and numerical calculations combined with finite-element method (FEM) analysis are performed in [21,22].…”