Numerical investigation of oil flow and temperature distributions for ON transformer windings

Failure of a transformer is a costly incident which can impact power system operation and result in loss of supply to customers. Transformers can fail through a number of mechanisms, one of which is from the formation of bubbles within the insulation. Currently, the loading guidance is set to avoid certain overload temperatures as high temperature is the main cause of bubbles forming. This paper analyses the limit set within the loading guides, comparing the most commonly cited temperature limit of 140°C with values taken from across the full spectra of available studies in literature. It is concluded that there is sufficient evidence for further investigation into formation of bubbles from transformer insulation as employing a single temperature limit may be inadequate. Use of a single temperature value is unsuitable, given the wide range of potential scenarios that the transformer fleet can present. It has become the go-to rationale that the moisture content of the solid insulation is the key driver for transformer bubbling temperature. This is true, however, it is shown that other factors such as solid insulation aged condition (determined through degree of polymerisation value) and the insulation type are also important considerations.

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“…Fig. 2 shows the plot of the results from (3) and (4). It can be seen that some deviation occurs between the two.…”

Section: History and Developmentmentioning

confidence: 96%

“…The formula as presented in [31] was adopted by Oommen and Lindgren as part of their equation for bubble formation [12]. The formula (for gas free systems) 'as used' is shown in (3) [32]; the corrected version is in (4). Fig.…”

Section: History and Developmentmentioning

confidence: 99%

Analysing the power transformer temperature limitation for avoidance of bubble formation

et al. 2019

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“…Through the thermal convection of transformer oil, winding losses are transferred to an oil tank, and the temperature is increased. The Mach number of transformers is small, and the steady-state mass conservation equation [21] of incompressible flow is as follows:…”

Section: B Electromagnetic-flow-thermal Couplingmentioning

confidence: 99%

Research on the Thermal-Electric Coupling Behavior Under Compound AC-DC Voltage Within Saddle-Like Electric-Stress Dependence

et al. 2020

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This paper proposes a nonlinear electromagnetic-thermal-velocity coupling model to study the insulation performance of converter transformer, in which the saddle-like electric-stress dependence is considered under compound alternating current-direct current (AC-DC) voltage situation. Firstly, the conductance of transformer oil and oil-immersed pressboard have been measured through constructed threeelectrode experimental system. An interesting electric-stress characteristic, which is saddle-like electricstress dependence is obtained and counted in the thermal-insulation analysis in the proposed model. Then, the high-order harmonics of compound AC-DC voltage have been considered in the built electromagneticthermal-velocity coupling model. Additionally, the impact of non-uniform temperature result has been mapped to the electric field domain through interpolation method, due to different meshes between the flowthermal and electric fields in accordance with distinct computational characteristics. Finally, the performance of nonlinear thermal-electric coupling properties, including saddle-like electric-stress dependence, have been considered in the proposed coupling model. Results determine that saddle-like thermal-electric dependent properties would considerably change insulation capability, compared with results from the traditional method. Even intensity field of some sampling points could jump more than 1.6 kV/mm. Therefore, it is essential to evaluate the insulation design by practical saddle-like electric-dependent properties. INDEX TERMS Compound ac-dc voltage, converter transformer, electric-stress dependence, finite element sub-model, electromagnetic-thermal-velocity coupling.

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“…Zhang et al [1] presented numerical study for oil stream and temperature distribution for disc-type of power transformer in an oil natural (ON) cooling mode. The study including the dimensional analysis by using Boussinesq approximation, for fixed the power loss distribution, winding geometry, volumetric flow fraction in each horizontal cooling duct and the dimensionless temperatures in the winding, they noted that in a relatively small and fixed range of Richardson number (from 0.4 to 0.6) regardless of the values of Reynolds and Prandtl num-THERMAL SCIENCE: Year 2019, Vol.…”

Section: Introductionmentioning

confidence: 99%

“…The experimental results of reduced model compared with CFD simulations and a significant convergence of results was found. Zhang et al [1] studied a numerical model of a disc-type transformer windings for ON cooling mode. The case study was proposed by using CFD programs.…”

Section: Introductionmentioning

confidence: 99%

Heat transfer enhancement from power transformer immersed in oil by earth air heat exchanger

Hannun

Hammadi²,

Khalaf

2019

THERM SCI

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In this study, the modelling of power transformer with (250 kVA) by using (AN-SYS17.1/FLUENT) code program was done. The power transformer was connected with earth air heat exchanger to decrease the temperature of (oil, core, and coils) of transformer which will increase its efficiency for preventing the damage and/or failure. The case study used the weather conditions of Nasiriya city, Iraq, at July 1 st with 50 °C as maximum ambient temperature and full electrical load of the power transformer. In addition to different pipe diameter, length of earth air heat exchanger and different air velocity entering to pipe. The results showed the temperature of (oil, core, and coils) for power transformer decreased with increase the pipe length and earth air heat exchanger depth underground. The air velocities inlet to earth air heat exchanger that used in the study were (2, 4 , and 6 m/s, respectively) and the results showed the increasing of air velocity inlet to earth air heat exchanger should decrease the temperature of (oil, core, and coils) for power transformer and increase the thermal conductivity of oil. The study concluded when using earth air heat exchanger in the power transformer and performance of power transformer will be increasing and led to decrease the temperature of oil about (18.5 °C).The results showed a significant convergence with previous researches.

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Numerical investigation of oil flow and temperature distributions for ON transformer windings

Cited by 54 publications

References 13 publications

Analysing the power transformer temperature limitation for avoidance of bubble formation

Analysing the power transformer temperature limitation for avoidance of bubble formation

Research on the Thermal-Electric Coupling Behavior Under Compound AC-DC Voltage Within Saddle-Like Electric-Stress Dependence

Heat transfer enhancement from power transformer immersed in oil by earth air heat exchanger

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