Transformer Temperature Rise Research Articles

Multi-Physics Coupling Simulation of Heat Transfer in Transformer Winding

In the electric power industry, the requirements for capacity, voltage level and compactness of transformers are getting higher and higher, which lead to significant problems, such as increased loss and more serious hot spots phenomena. Based on the three-dimensional finite element method, this paper establishes the bidirectional coupling between electromagnetic field, flow field and temperature field to calculate the temperature rise of 400 kVA oil-immersed transformer at full load and compare it with the results obtained by the heat-flow unidirectional coupling method (constant loss). The results show, due to the interaction between electromagnetic field and temperature field, the coil loss density increases, but the core loss density does not change. The hot spot temperature of coil increases and the location of coil hot spot changes. The temperature and position of the core hot spot do not change. The loss density of coil decreases as the inlet velocity increases, the hot spot temperature of coil drops faster. When the inlet velocity exceeds 0.5 m/s, increasing the inlet velocity can no longer effectively promote heat exchange. With the increase of the inlet velocity, the interaction between electromagnetic field and temperature field is weakened, but it still has a great impact on the loss density of coil. The multi-physics coupling method is of great significance to improve the accuracy of transformer temperature rise calculation.

Research on the temperature rise characteristics of power transformers based on fluid-solid-thermal coupling

The problems of overheating and insulation are the main influencing factors to the operation status of power transformers. Based on the physical model of a 50MVA/110kV oil-immersed self-cooling transformer, the electromagnetic, temperature and fluid field are introduced to establish a three-dimensional temperature rise model of the transformer in this thesis. The loss obtained from the electromagnetic field calculation model is taken as a heat source and input into the transformer temperature rise model. The results show that the hot spot temperature occurs in the core column and increases with the maximum load current when the single-phase ground fault occurs, and the hot spot temperature in the transformer exceeds the limit value. The temperature distribution trends of the core and high and low voltage windings under rated conditions and overload conditions are similar. In addition, the average temperature rise of the windings under overload conditions exceeds the limit value.

Impact of high-frequency harmonics (0–9 kHz) generated by grid-connected inverters on distribution transformers

The level of current harmonics circulating in a transformer winding can affect its operating temperature and lifetime. Although the existing standards mainly consider the impact of harmonics up to 2 kHz, higher frequency harmonics generated by high power converters utilized in renewable energy sources can also contribute to the temperature rise of a transformer. Pulse Width Modulated (PWM) voltage generated by power converters can generate significant high-frequency harmonics at its switching frequency. The switching frequency of converters in high-power applications is mainly between 2 and 9 kHz. Consequently, in this article, the importance of also using higher frequency harmonics in calculating transformer core loss and temperature rise is investigated as per IEEE standard conclusions. For that purpose, transformer K-factor values have been calculated in simulated and practical distribution systems, in both long-term and transient conditions. The results confirm the importance of considering higher-order current harmonics (more than 2 kHz) when calculating K-factor and estimating transformer temperature rise and lifetime.

HST calculation of a 10 kV oil‐immersed transformer with 3D coupled‐field method

Transformer winding hot-spot temperature (HST) is one of the important factors affecting transformer oil–paper insulation deterioration. This study presents a three-dimensional coupled electromagnetic-fluid-thermal analysis method for HST calculation in a 10 kV oil-immersed distribution transformer, the influence of the transformer internal metal structure parts on the HST of the winding is considered in the simulation. Combining electromagnetic-field calculation with no-load test and load test of the transformer provides a more accurate method to determine internal losses of the transformer. Taking those power losses as heat sources, the transformer fluid-thermal field analysis is conducted with the finite volume method. The variation of physical parameters of transformer oil with temperature is considered in the simulation. On the basis of the equivalent thermal resistance theory, the equivalent thermal conductivities of transformer windings are obtained. The simulation results deduced from the proposed method agree well with the experimental ones, which are obtained with fibre optic temperature sensors during the transformer temperature rise test, the maximum temperature difference is <3°C. The results validated the validity and accuracy of the proposed transformer HST calculation method.

Thermal analysis and derating of a power transformer with harmonic loads

Thermal conditions of power transformers in abnormal operating conditions such as harmonic loads can be considered as a critical case. In this study, thermal analysis of transformer and additional imposed heat on it, caused by non-linear loads, are addressed. For this purpose, an appropriate thermal equivalent circuit is used in which temperature of different parts of oil-immersed power transformers are obtained for harmonic loads. The losses of various components of transformer as heat-generating sources are estimated. At this end, an appropriate three-dimensional finite element method is applied to estimate the losses of different parts of transformer. To keep the transformer temperature rise around the permissible value, the transformer is derated. Transformer derating based on the IEEE Std C57.110–2008 recommendation considerably reduces the transformer loading capability. Therefore, this study introduces a new technique for derating of transformer for harmonic loads. This enhances the transformer thermal limits and transformer loading capacity.

Study on the Method of Calculating Temperature Rise of Transformer

The internal temperature of the transformer is a key parameter to measure the thermal state of the transformer. The service life of the transformer generally depends on the life of the insulating material, and high temperature is the main reason why cause insulation aging, this paper studies the temperature rise of transformer winding hot spot temperature for the key, using the neural network forecasting method, forecasts transformer winding hot spot temperature change rule, calculate the transformer internal temperature rise, provide the temperature of the scientific basis for the safe operation of the transformer.

Transformer oil-based magnetic nanofluid with high dielectric losses tested for cooling of a model transformer

An experimental study of dielectric permittivity and dissipation factor of transformer oil-based magnetic nanofluid is reported in this paper. The investigated nanofluid consists of a commercial transformer oil and iron oxide nanoparticles (0.93 % solid volume fraction) coated with oleic acid as a stabilizing agent. Both, the transformer oil and the nanofluid were subjected to measurements of dielectric permittivity and dissipation factor under 1 kV at a power frequency of 50 Hz in the temperature range from 303 to 373 K. The compared results show that the magnetic nanofluid exhibits approximately 4 orders of magnitude greater dielectric losses than the transformer oil. This raised a question about the suitability of such a nanofluid for cooling applications in a transformer. Therefore, the cooling effectiveness of the nanofluid was tested in a model single-phase power transformer under 4.3 kVA load. The prototype transformer was designed with the aim to monitor its temperature at various locations during the load test. It was found that the cooling with the lossy nanofluid does not result in the deterioration of the thermal conditions of the transformer as compared to the cooling with the transformer oil. On the contrary, the tested nanofluid provides a slight decrease in the average transformer temperature rise. Possible reasons accounting for the slight enhancement in the transformer cooling are discussed. The increased thermal conductivity and development of thermomagnetic convection are considered as primary reasons of the cooling effect.

Automatic System for Temperature Rise Test in Power Transformers

The hot spot temperature value is one of the most important parameters governing the operating life of power transformers. This article presents the implementation of an automatic system for the determination of the hot-spot temperature in power transformers in accordance with the international standards. It presents the architecture and the main components of the proposed automatic system, which is modular, reliable and performs the acquisition, processing, transmission, storage of electrical and nonelectrical quantities and determines the parameters of the transformer temperature rise in test benches. In order to avoid the presence of individuals in dangerous areas with high potential around the transformers, wireless technology is used to transfer the quantities acquired from the sensors placed on the power transformer. The proposed system implements the calculation methodology prescribed by the standard, achieves a historical database of the test and also a synthetic automatic report which is sent to predefined email addresses. To achieve the viewing of results remotely while maintaining a high level of data security, software modules are implemented to allow the specialists at remote locations with access rights to connect to a cloud platform. The results obtained for a 200/200/60MVA and OFAF cooled type power transformer are used for the validation of the automatic system.

A Data-Driven Residential Transformer Overloading Risk Assessment Method

Residential transformer population is a critical type of asset that many electric utility companies have been attempting to manage proactively and effectively to reduce unexpected failures and life losses that are often caused by transformer overloading. Within the typical power asset portfolio, the residential transformer asset is often large in population, having lowest reliability design, lacking transformer loading data and susceptible to customer loading behaviors such as adoption of distributed energy resources and electric vehicles. On the bright side, the availability of more residential operation data along with the advancement of data analytics techniques have provided a new path to further our understanding of local residential transformer overloading risks statistically. This research developed a new data-driven method to combine clustering analysis and the simulation of transformer temperature rise and insulation life loss to quantitatively and statistically assess the overloading risk of residential transformer population in one area and suggest proper risk management measures according to the assessment results. Case studies from an actual Canadian utility company have been presented and discussed in detail to demonstrate the applicability and usefulness of the proposed method.

A Method for Hot Spot Temperature Prediction of a 10 kV Oil-Immersed Transformer

This paper proposed a prediction method to predict a 10-kV oil-immersed transformer hot spot temperature (HST). A set of feature temperature points on the transformer iron shell is proposed based on fluid-thermal field calculation. These feature points, as well as transformer load rate, are taken as the input parameters of a machine learning model established by support vector regression (SVR), thus to describe their relationships with the HST. This model is trained by nine samples selected by L9(34) orthogonal array and applied to predict the HST of 20 test samples. The training samples are all obtained by simulation, and the test samples have consisted of simulation and transformer temperature rise test results. With effective parameter optimization of the SVR model, the predicted results agree well with the experimental and simulation data, the mean absolute percentage error (MAPE) is 1.55%, and the maximum temperature difference is less than 3 °C. The results validated the validity and the generalization performance of the prediction model.

THE Simulation Study of DC Grounding Electrode Based on CDEGS and ANSYS

When the UHVDC project was put into operation, grounding electrode grounding current may affect the transformer in the substation near the pole, it will cause transformer DC bias saturation, which leads to higher transformer temperature rise, too high harmonic and reactive power consumption, which will cause transformer damage or power grid blackout. The earth resistivity model of grounding pole is not accurate enough and the calculation of surface potential distribution is not accurate enough, which will cause the deviation between the evaluation and actual damage degree before and after the project put into operation. In order to simulate the grounding potential distribution directly after grounding, the simulation analysis with different methods can be checked with each other, and the related design units used CDEGS to simulate the earth potential rise. In this paper, the influence of DC transmission grounding electrode on the distribution of ground surface potential is analyzed, and the calculation method of DC grounding electrode current field is deduced. The 6 layers earth soil model was established. CDEGS and ANSYS were applied. The earth potential rise distribution in the 0~100 km radius of the earth electrode was calculated respectively. In this paper, the results of the earth potential distribution in the 0-50 km range of the two schemes were compared and analyzed. The results show that the calculation results of ANSYS were slightly smaller than those calculated by CDEGS, and the difference was about 0.6 V. The calculation results of the two schemes could provide reference for field practical monopole operation and commissioning.

Temperature field simulation research on the leakage inductance transformer

The structural and electrical parameters of leakage inductance transformers can significantly affect the efficiency, noise, and vibration of microwave ovens. The paper proposed a new iron core structure with finite element modeling and simulations of a leakage inductance transformer by both the electromagnetic field and system design simulation software. Different silicon steel sheet models were used for the upper and lower parts of the proposed iron core to reduce the loss and heat of the leakage inductance transformer. The iron core scheme was changed from the traditional E-I type to the E-E type. The feasibility of the new iron core scheme was tested by numerical results which showed that the maximum temperature rise of the leakage inductance transformer decreased significantly.

Designing Optimal Passive Filters for Transformers under Harmonic Conditions

Power transformers are designed to supply linear loads at nominal frequency; however, the development of power electronic devices and controllable loads that is generally called non-linear loads is promotion. Non-linear loads lead to temperature rise of transformers significantly and causes decrease their lifespan dramatically. In addition harmonics causes reduced power factor, which causes to reduce active power delivered to consumers. One of the methods to prevent and reduce harmonics is to use C-type passive filters regarding their advantages over other types of filters. Determining the relevant parameters is prerequisite to the application of such filters.In this paper, model of distribution transformer considering the effects of harmonic and saturation with C-type passive filters is optimized. Performance of different optimizing methods is compared with each other in optimization of model’s parameters. Simulation results shown the invasive weed optimization method is an intelligent optimization method with appropriate performance compared with other methods.

Effects of voltage harmonic on losses and temperature rise in distribution transformers

The effects of harmonic pollution in the power system on distribution transformer losses and temperature rise have become an increasing concern. The pollution can be in the form of current and/or voltage harmonics present in the supply networks. Since the impact of voltage harmonics has hardly been investigated, this study examines the effects of distorted voltage excitation on oil-filled distribution transformers. Short-circuit and open-circuit tests were conducted on two distribution transformers. The results revealed significant increase in both losses and temperature. An equation is developed to quantify the power loss. This study also derives an equation to evaluate the resistance corresponding to the eddy-current loss.

Selection of an optimum flux density to offer reduced core loss and its effect on temperature rise of transformers

Commonly used grades for transformer core stampings are Cold Rolled Grain Oriented Steel of grades M3, M4, M5 and M6. As the flux density increases, the magnitude of no load loss and no load current increases. But studies also indicated that, a given magnitude of core loss can be attained with both high and low magnitudes of no load current. This result can be used to ascertain the presence of inferior grade core material. It is essential to operate the transformer in the linear region of BH curve. Operation in saturated state will result in increased no load current which in turn will have a detrimental effect on the temperature rise of transformer as additional I2R losses are generated. With the limits of temperature rise being more stringent in IS standard than in IEC, the choice of flux density is crucial. In this paper an attempt is made to realize the best operational flux density, which gives a benchmark for deciding the magnitude of no load current and the corresponding no load power factor.

Performance Comparison of Carbon Nanotubes with Copper and Aluminium as Winding Material in Transformer

Objectives: Transformers are used in almost every industry; therefore further improvement in their efficiency is always desirable. The objective of this work is to study the potential of Carbon Nanotubes to replace copper/aluminum in transformers. Methods/Analysis: In this work, FEM (Finite Element Method) technique based planar model of an aluminum-wound transformer is developed in FEMM software. The magnetic and steady state heat flow analysis of this transformer has been carried out. Then, the thermal and electrical properties of aluminum windings are replaced with that of new carbon based nanomaterial; Carbon Nanotubes (CNTs) and copper respectively to measure the effect on the performance of the transformer. Theoretical electrical conductivity of CNTs, which is much higher than that of macroscopic yarns till date, has been used. Findings: The comparison of maximum winding I2R losses and maximum winding temperature rise, when winding material is taken as aluminum, copper and CNT respectively, has been done. Also, weight of the conductor required has been compared. Maximum winding I2R losses and maximum winding temperature rise obtained in case of CNTs are lower than that in case of copper and aluminum. Weight of the conductor is also less than copper/aluminum. Application/Improvement: Previous work on use of CNT windings in transformer have demonstrated that it works in accordance with the classical theory of transformers. In this work, the effect on transformer winding losses and temperature rise has been analyzed when conventional winding materials are replaced by CNTs.

Determination of Wound Core Transformer Losses and Temperature Rise

Recently tape wound cores are widely used in transformers for power electronics applications. The spiral structure of theses cores affects the flux distribution inside the core and causes complication of magnetic analysis. In this paper, a model based on reluctance networks method is used for analysis of magnetic flux in toroidal wound cores and losses calculation. A Preisach based hysteresis model is included in the model to consider the nonlinear characteristic of the core. Magnetic losses are calculated by having the flux density in different points of the core and using hysteresis model. Additionally a thermal equivalent circuit is applied to determine the temperature rise in transformer due to the magnetic and electric losses. A transformer for using in a series resonant converter is modeled and the results are compared with experimental measurements to evaluate the validity of the model. Comparisons show accuracy of the model besides simplicity and fast convergence.

A Novel Approach to Investigate the Hot-Spot Temperature Rise in Power Transformers

For large power transformers, the hot-spot temperature rise in their structural parts is an essential issue to address. Computation of the hot-spot temperature rise is, however, a complicated engineering problem because of the uneven loss distribution and effect of internal oil flow upon the convective heat transfer coefficients on the body surfaces of transformers. This paper presents a novel approach to compute and analyze the hot-spot temperature rise of the structural parts for an ODFS-334 MVA/500 kV single-phase auto-transformer. The surface convection heat transfer coefficients, which are computed based on computational fluid dynamics, are used as the boundary conditions of the magnetic-thermal coupling analysis using finite-element method. To validate the feasibility and applicability of the proposed method, the numerical results obtained from the proposed method are compared with those of experimental ones.

Preliminary Analysis on the Interplanetary Cause of Geomagnetically Induced Current and Its Effect on Power Systems

Using the detected events of geomagnetically induced current (GIC) in the Ling’ao nuclear power plant from 2004 to 2005, and focusing on the interplanetary cause of GIC and its effect on power systems, we have analyzed the corresponding solar driving sources and interplanetary solar wind structures, and performed spectral analysis on the most intense GIC event by means of wavelet transform. The results of this study show that: (1) Most GIC events were driven mainly by the halo coronal mass ejections, the interplanetary cause of GIC events includes the shock sheath, magnetic cloud, and multiplex interplanetary solar wind structure. (2) Based on the strongest GIC event on 2001 November 9, we find that the fluctuation of GIC in the earlier stage was related to the magnetic cloud boundary layer, and the variation of GIC intensity in the later stage was caused by magnetic cloud itself. (3) Compared to the frequency of the power system (50 Hz), the GIC can be equivalent to a quasi direct current. The energy of the GIC is embodied in the two time intervals in the wavelet power spectrum: the first interval is shown as an impulsive type and with a weaker intensity, and the second one is stronger. Regarding to the cumulative time of the transformer temperature rise caused by GIC, the second interval has a longer duration than the first one. Hence, during the second interval, it is more harmful to the power systems and devices. (4) With a correlation analysis, the correlations of the SYM-H index and dBx/dt with the GIC are significantly stronger than those of other geomagnetic indices with the GIC.

Study on Temperature Rise of Dry-Type Transformer in Different Cooling Conditions with FEM

To study the temperature rise of dry-type transformer in different cooling conditions, finite element method is used in this paper to calculate temperature distribution in the transformer. Firstly, thermal-fluid coupled model of a transfomer is built up，and the equivalent heat generation of this model is figured out according to the results of delivery test. Then, thermal-fluid coupled model is simulated in both natural cooling condition and forced cooling condition, and temperature distributions in the iron and windings under these two conditions are obtained. Finally, temperature rises in these two conditions are compared to figure out the influence of cooling condition on transformer temperature rise.