Heat transfer in power transformer windings with oil-forced cooling (original) (raw)
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Power Transformer Winding Thermal Analysis Considering Load Conditions and Type of Oil
Power transformer outages have a considerable economic impact on the operation of an electrical network. In order to draw maximum power from transformers and, at the same time, avoid thermal mishaps, it is essential to carefully study its thermal behavior. Furthermore, an accurate computation of the hottest spot temperature (HST) helps in a realistic estimation of the reliability and remaining life of the transformer winding insulation. This paper presents steady state temperature distribution of a power transformer layer-type winding using conjugated heat transfer analysis, therefore energy and Navier-Stokes equations are solved using finite difference method. Meanwhile, the effects of load conditions and type of oil are investigated using the model. Oil in the transformer is assumed nearly incompressible and oil parameters such as thermal conductivity, special heat, viscosity, and density vary with temperature. Comparing the results with those obtained from finite integral transform checks the validity and accuracy of the proposed method.
International Journal of Emerging Electric Power Systems, 2008
The power transformer is a complex and critical component of the power transmission and distribution system. System abnormalities, loading, switching and ambient condition normally contribute to accelerated aging and sudden failure. In the absence of critical components monitoring, the failure risk is always high. For early fault detection and real time condition assessment, an online monitoring system in accordance with the age and conditions of the asset would be an important tool. Power loss, heat generation and heat distribution evaluations in a large-scale oil immersed power transformer are presented here, along with the details of computer implementation and experimental verification.Core power losses are approximately constant with temperature variation or may decrease with that. Over the temperature range of 20 to 100°C the change in hysteresis loss Ph with temperature was negligible. Since the total core loss PT decreased with increasing temperature over this range, almost ...
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Inordinate localized temperature rise in the power transformer causes subsequent thermal breakdown. To prescribe the limits of short-term and long-term loading capability of a transformer, it is necessary to estimate the hottest spot temperature (HST) of transformer. This paper proposes the steady state temperature distribution of the power transformer windings. Oil in the transformer is assumed nearly incompressible and oil properties such as thermal conductivity, special heat, viscosity, and density vary with temperature. Finite difference method is used for numerical solution. The selected model for simulation is a 50KVA, 20 kV/400V oil natural, and air natural cooling (ONAN) power transformer. A Comparison of the author's results with those obtained from finite integral transform and experimental test confirms the validity and accuracy of the proposed method.
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Since large power transformers belong to the most valuable assets in electrical power networks, it is suitable to pay higher attention to these operating resources. Thermal impact leads not only to long-term oil/paper-insulation degradation; it is also a limiting factor for the transformer operation. Therefore, the knowledge of the temperature, especially the hot-spot temperature (HST), is of high interest. The calculation of current thermal stress helps to avoid unexpected outages. This paper presents the temperature distribution in windings of the oil power transformers. In this paper, energy (thermal) equation is solved until temperature is obtained. Oil in the transformer is assumed nearly incompressible and oil parameters such as thermal conductivity, special heat, viscosity, and density vary with temperature. For numerical solution of above equation, finite element method is used. The selected models for simulation are 300 KVA and 22.5 MVA ONAN transformers.
This paper summarise a few computational methods and engineering models proposed for transformer thermal analysis and the accurate prediction of transformer thermal characteristics. The paper presents different approach for numerical calculation of thermal field distribution in power transforemer. The model presented facilitates the establishment of criteria for optimizing transformer operation under various load conditions, environments as well as in the case of failures. Thus, the transformer can operate at maximum capacity while, at the same time, the probability of faults due to overheating is reduced to a minimum. The choice of combination of oil and insulation material specifies transformer properties and directly influences on its field of application. Unconventional insulation systems are for example transformer insulation systems where mineral or some other type of oil is used as liquid dielectric. Coupled physical and mathematical models would assist in the development of ...
IEEE Transactions on Power Delivery, 2004
The degradation of electrical insulation in transformers is traced to thermoelectric processes. Existence of localized hot regions due to thermal insulating properties of electrical insulation would cause thermal runaway around these regions. In an earlier paper [1], the authors presented analytical methods for estimating the temperature and its distribution at different points of the transformer based on a closed-form mathematical technique using a generalized heat conduction (GHC) model. Certain aspects of the inhomogeniety of the several components of the winding and incorporation of distributed heat source were not addressed. Also, a rigorous treatment involving the changes in winding resistance, which was built into the thermal model as an empirical correction factor, has now been modified and incorporated in the GHC. These considerations have now improved the accuracy of estimation of hottest spot temperature.
Development of an Improved Model for Assessment of Hot Spot Temperature of Current Transformers
IJEER, 2018
░ABSTRACT: Current transformers form important components that make up a large portion of capital investments. Failure of a current transformer results in an adverse effect in the operation of transmission networks which causes an increase in the power system operation cost and inability to deliver electricity with absolute reliability. The age of a transformer is the life of its insulation, majorly, paper insulation. Transformer aging can be evaluated using the hot spot temperature which has the effect of reducing the insulation life of transformers. Previous researchers have developed models for assessment of top-oil temperature of current transformers. Such models have the limitation that they do not accurately account for the variation effect in ambient temperature and hence not applicable for an on-line monitoring system. This research paper develops an improved model for assessment of hot spot temperature from the IEEE top-oil rise temperature model by considering the ambient temperature at the first-order characterization using appropriate mathematical notations. The ambient temperature, top oil rise over temperature and winding hot spot rise over temperature were used as input parameters for the development of the improved hot spot temperature model by considering the final temperature state since the time-rate-of change in top-oil temperature is driven by the difference between the exits top-oil temperature for ambient temperature variation. The improved model was then implemented in MATLAB to compute the hot spot temperature for 24-hour load cycle. The result of the improved model shows that the least and highest value of the hot spot temperature are 63 0 C and 105.4 0 C respectively indicating a retardation in the aging process of the transformers. The improved model helps to minimize the risk of failure and to extend the life span of transformers thereby controlling the hot spot temperature rise and top oil temperature.
Two-dimensional finite element thermal modeling of an oil-immersed transformer
European Transactions on Electrical Power, 2008
Finite element (FE) modeling of a typical transformer indicates that the hot spot position is always on the top most part of the transformer. The hot spot temperature of winding depends on the load and the type of loading and is changed by loading. A number of the generated magnetic flux lines of windings close to their paths perpendicular to the internal channel of the windings and therefore the flux density in the middle of the channel is considerably larger than the beginning and ending of the winding. Two models of windings are employed and different temperature distributions are obtained. The computation results show that the time constant of high voltage (HV) winding is lower than that of the low voltage (LV) winding. A good agreement between the test and computed results has been achieved.
Investigating and calculating the temperature of hot-spot factor for transformers
Indonesian Journal of Electrical Engineering and Computer Science
This article explores the measurement of temperature in transient states, utilizing the principles of heat transfer and thermal-electrical metaphor. The study focuses on the nonlinear thermal resistances present in various locations within a distribution transformer, while taking into account variations in oil physical variables and temperature loss. Real-time data obtained from heat run tests on a 250-MVA-ONAF cooled unit, conducted by the transformer manufacturer, is used to verify the thermal designs. The observations are then compared to the loading framework of the IEC 60076-7:2005 system. The findings of this research provide a better understanding of temperature measurement in transient states, particularly in distribution transformers, and can be applied to the design and development of more efficient and reliable transformer systems.
Computer Modeling in Engineering & Sciences, 2021
The distribution transformer is the mainstay of the power system. Its internal temperature study is desirable for its safe operation in the power system. The purpose of the present study is to determine direct comprehensive thermal distribution in the distribution transformers for different loading conditions. To achieve this goal, the temperature distribution in the oil, core, and windings are studied at each loading. An experimental study is performed with a 10/0.38 kV, 10 kVA oil-immersed transformer equipped with forty-two PT100 sensors (PTs) for temperature measurement installed inside during its manufacturing process. All possible locations for the hottest spot temperature (HST) are considered that made by finite element analysis (FEA) simulation and losses calculations. A resistive load is made to achieve 80% to 120% loading of the test transformer for this experiment. Working temperature is measured in each part of the transformer at all provided loading conditions. It is observed that temperature varies with loading throughout the transformer, and a detailed map of temperature is obtained in the whole test transformer. From these results, the HST stays in the critical section of the primary winding at all loading conditions. This work is helpful to understand the complete internal temperature layout and the location of the HST in distribution transformers.