Experimental study of dynamic thermal behaviour of an 11 kV distribution transformer (original) (raw)
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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.
Power Transformer Temperature Evaluation for Overloading Conditions
IEEE Transactions on Power Delivery, 2005
The calculation methodologies of transformers' hottest spot and top oil temperatures are evaluated in this paper. Thereafter, a comparison between the calculated and the values obtained during the assessment of a transformer factory test was realized. The referred tests were conducted using an ONAF type, 30/40 MVA, 138/13.8 kV transformer, in which sensors with fiber-optic cables, to record directly the internal parameters, were installed. In a first series of tests, transformer loadings corresponding to 100%, 70% and 116.5% of rated power, were used. The tests were completed by applying values of a daily load profile with several hourly power levels. Additionally, in two of the hourly periods, high temporary loadings one of 160% during 30 minutes, and another of 170% during 15 minutes, were applied.
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.
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.
Dynamic Thermal Model for Power Transformers
IEEE Access
The prediction and determination of thermal response for the metallic parts is a very crucial step in the design of power transformers. This paper presents a comparative analysis of different thermal models for predicting the hotspot temperature and top oil temperature of power transformers. Also, a new thermal model is proposed for the monitoring of transformer operation which is capable of identifying the hotspot temperature and the top oil temperature by taking into account the ambient temperature and the load variation with respect to real time. The model is experimentally validated and compared with the actual field data. It is found that results obtained from the proposed model and the actual field data are in good agreement. INDEX TERMS Transformer, hotspot temperature, transformer faults, thermal model.
2012
The most important parameter in transformers life expectancy is the hot-spot temperature level which accelerates the rate of aging of the insulation. The aim of this paper is to present thermal models for transformers loaded at prefabricated MV/LV transformer substations and outdoor situations. The hot-spot temperature of transformers is studied using their top-oil temperature rise models. The thermal models proposed for hot-spot and top-oil temperatures of different operating situations are compared. Since the thermal transfer is different for indoor and outdoor transformers considering their operating conditions, their hot-spot thermal models differ from each other. The proposed thermal models are verified by the results obtained from the experiments carried out on a typical 1600 kVA, 30 /0.4 kV, ONAN transformer for both indoor and outdoor situations.
Prediction of hottest spot temperature (HST) in power and station transformers
2003
The degradation of electrical insulation in transformers is more often due to thermal stress. In this paper authors have attempted to work out a means of assessing the magnitude of temperature and the hottest region in the body of a large transformer with a reasonable degree of accuracy. A theoretical model has been developed based on boundary value problem of heat conduction in transformer winding using finite integral transform techniques. The model requires, in addition to electrical parameters of the transformer, information on the actual design data. The authors believe that this model predicts HST with precision and also indicates a possibility of on-line data acquisition.
New Analytical Formula for Temperature Assessment on Transformer Tanks
2015
A rigorous analytical development is presented to find a formula that provides the temperature distribution in the tank zones close to bushings of distribution transformers. The new formula can be fed with a loss distribution obtained either analytically or numerically. This fact is shown using two proven loss distributions, combined with our new formula, and comparing their results with finite element simulations that use a pre-established loss distribution in one case and solve a thermal-electromagnetic coupled problem in the second case. An excellent match between numerical and analytical results is found, which are independently determined using completely different computation philosophies. As a result, it is clearly shown that our proposed formula is effective and accurate. Moreover, it requires much lower computational resources as compared to finite element simulations that require commercial or highly specialized software. Our formula will contribute to the better design of transformers, increasing their useful lives and reducing operating costs in power networks.
Different Hot-Spot and Top-Oil Temperature Models for Monitoring of Transformers
2014
One of the most important parameters governing a transformer’s life expectancy is the hot-spot temperature value. This paper presents accurate temperature calculation methods taking into account the above mentioned findings to estimate life of transformer form hot spot temperature. An attempt to find a proper dynamic top-oil temperature model to be used in an monitoring and diagnostic system for transformer is the aim of this paper. Through comparison of a measured value such as top-oil temperature, analizing thermal image of transformer, and calculated value top-oil temperature which is obtained by means of a physical model, operational problems can be detected. The experimental base of this research are the measurements on air core transformer realised with thermovision camera.
Predicting transformer temperature rise and loss of life in the presence of harmonic load currents
Ain Shams Engineering Journal, 2012
Power transformers represent the largest portion of capital investment in transmission and distribution substations. One of the most important parameters governing a transformer's life expectancy is the hot spot temperature value. The aim of this paper is to introduce hot-spot and top-oil temperature model as top oil and hot spot temperature rise over ambient temperature model and thermal model under liner and non-linear loads. For more accurate temperature calculations, in this paper thermal dynamic model by MATLAB is used to calculate the power transformer temperature. The hot spot, top oil and loss life of power transformer under harmonics load are calculated. The measured temperatures of 25 MVA, 66/11 kV, ONAF cooling temperatures are compared with the suggested dynamic model.