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Hot spot temperature (HST) is an important parameter reflecting the working state of the traction transformer, and the load characteristics have a great influence on the HST. The current researches rarely consider the load characteristics of transformers in-depth, and most of the research on the temperature field focuses on steady load. Therefore, a prediction model of HST for the traction transformer considering the load characteristics is established by the finite element simulation in this paper. Considering the impact and nonlinearity of traction load, the influence of the load characteristics on the HST is studied. Analysis of the load curve revealed that the steady and step load combination could well simulate the traction load. Based on the analysis of traction transformer load characteristics, the temperature field coupling calculation of traction transformer is carried out according to the VI normative duty class. On this basis, the influence of load rate and time on HST is studied. The present findings show that the method can predict the HST of traction transformer under different working conditions and provide a reference for load dispatching of traction transformer. The simulation data are in good agreement with the test results, and the average relative error is 3.4%. The results verify the effectiveness of the proposed method.

Dry-type transformers are rapidly becoming popular as wind turbine step-up (WTSU) transformers, especially in offshore wind farms. Cast resin transformers are not flammable and are also resistant to moisture. However, their thermalelectrical degradation must be carefully analysed given the special conditions of wind farm installations. The present paper studies the remaining useful life (RUL) calculation of dry-type WTSU transformers based on the most thermally stressed location i.e. the winding hot-spot. The estimation of the loss of life of the transformer can be used for diagnostic and prognostic monitoring purposes in the framework of digital twins. The methodology is then applied to a typical WTSU load profile and the impact of several transformer characteristics and operating conditions are compared to the reference case. The authors gratefully acknowledge the support of the Basque Government (project ELKARTEK KK2018/00096 and GISEL research group IT1191-19), as well as of the University of the Basque Country UPV/EHU (research group funding GIU18/181).

Hot spot as well as top oil temperatures have played the most effective parameters on the life of the electrical transformers. The prognostication of these factors is very vital for determining the residual life of the electrical transformers in the transmission and distribution systems. Thus, an accurate mathematical method is required to calculate the critical temperature such as hot spot and top oil temperature based on the different types of thermal models. In this study calculates the service life of the transformers based on an accurate top oil temperature. Accordingly, An approach solution is given for calculating the thermal model. Also, findings are validated with true temperatures. Finally, this method is implemented on 2500 KVA electrical transformer.

Transformer thermal modelling is a crucial aspect to be considered as this may help the determination of heat capacity of transformer. This paper present, simulation study on Oil Natural Air Natural (ONAN) transformer heat distribution pattern with and without presence of hot spot temperature (HST). This paper aims to compare the effects of different HST value at different locations inside the transformer unit as well as to evaluate the top oil thermal behaviour of corn oil as cooling mechanism in a transformer. To achieve aforementioned objectives, three HSTs were introduced to the 30 MVA transformer winding to find the total heat build-up in the top of the transformer tank. The outcome of thermal properties is examined using x-y temperature plot. From the results found that the location of HST affects overall transformer’s temperature. HST at the top of the winding give a significant effect compared to when HST is at the bottom of the winding. It is also evident that the usage of corn oil reduced the temperature distribution of the transformer. The findings suggest that the temperature distribution study especially on transformer is important to monitor in-service transformer in a non-invasive manner.

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 transformer bushing hot spot temperature (HST) seriously affects its performance and design. In this paper, a novel method for calculating the hot spot temperature of bushing is proposed, in which the principle of constant joule heat is adopted to transform the fluctuating current into the steady-state current. Firstly, the fluctuating current based on time is segmented. Then, the fluctuating current in each period of time is transformed into steady-state current which is used as heat source. Next, the Finite Element Method (FEM) is used to determine a typical bushing's temperature distribution and specify its hot spot. According to the calculation results of hot spot temperature rise, the time interval is adjusted. Finally, the optimal time interval and the steady-state equivalent current are obtained by solving the hot spot temperature of the transformer bushing iteratively. In addition, the method is used to calculate the hot spot temperature of a 220kV Oil Impregnated Paper (OIP) bushing. Compared with the results of traditional transient calculation method, the validity of the proposed method is verified, and the computing time is greatly reduced.

The European DEMOnstration Fusion Power Plant (EU-DEMO) is being designed as an intermediary stage between the ITER experimental reactor and future commercial fusion power plants. The EU-DEMO is based on the tokamak concept with a fully superconducting magnet system. The Central Solenoid (CS) of the EU-DEMO will consist of five modules, namely: CSU3, CSU2, CS1, CSL2 and CSL3, located vertically one above the other. The central CS1 module will be subjected to the most demanding operating conditions (the highest magnetic field and mechanical loads). Two concepts of the CS1 winding pack (WP) are being designed by CEA IRFM (France) and EPFL-SPC (Switzerland) teams. The pancake wound WP proposed by CEA is based on Wind & React Nb3Sn Cable-in-Conduit Conductor, whereas the hybrid WP developed by EPFL-SPC consist of 10 sub-coils, layer-wound using: HTS (RE-123), React & Wind Nb3Sn and NbTi conductors in the high, medium and low field sections, respectively. Each design iteration undergoes comprehensive electromagnetic, mechanical and thermal-hydraulic analyses aimed at verification if it fulfils the design performance criteria. Our present work is focused on the quench analysis of all the hybrid CS1 sub-coils, aimed at the assessment of the maximum hot-spot temperature. The analysis, based on the iteration of the hybrid design proposed in 2017, is performed using the THEA CryoSoft code. We assume that quench is initiated at the beginning of premagnetization phase and include in our model the realistic magnetic field distribution along each conductor computed with 2D axi-symmetrical finite element model in ANSYS. We study the effect of taking into account heat transfer between neighbouring turns and heat generation due to AC losses during the fast discharge on the value of the hot spot temperature.

In addition to a reduced number of feeders, which would simplify their integration in the cryostat of the tokamak, the present study considers the possibility to reduce the voltage during safety discharge of the toroidal field (TF) coils. A lowered discharge voltage would ease the manufacture of the TF coils and reduce the operational risks. Both aspects closely related to the discharge time constant, determined by the ratio LTF/Rd, where Rd is the resistance of the dump resistor and LTF the inductance of the TF coil. The supply of current to two or more TF coils in series requires a reduced discharge voltage per TF coil. The present study considers a fixed total TF current of 14.9 MA-turn provided by the DEMO baseline 2018. The discharge voltage can be reduced by increasing the TF conductor current, and hence lowering the inductance, or by an enlarged discharge time constant. For an increased discharge time constant, the copper cross-section in the TF winding pack needs to be increased to limit the hot spot temperature to acceptable values. A parametric study of the impact of increased TF conductor currents and discharge time constants on the radial build of the TF winding pack has been performed. The advantages of a possible reduction of the TF discharge voltage need to be compared with the disadvantages of an increased radial build.

This paper develops a novel dynamic correction method for the reliability assessment of large oil-immersed power transformers. First, with the transformer oil-paper insulation system (TOPIS) as the target of evaluation and the winding hot spot temperature (HST) as the core point, an HST-based static ageing failure model is built according to the Weibull distribution and Arrhenius reaction law, in order to describe the transformer ageing process and calculate the winding HST for obtaining the failure rate and life expectancy of TOPIS. A grey target theory based dynamic correction model is then developed, combined with the data of Dissolved Gas Analysis (DGA) in power transformer oil, in order to dynamically modify the life expectancy calculated by the built static model, such that the corresponding relationship between the state grade and life expectancy correction coefficient of TOPIS can be built. Furthermore, the life expectancy loss recovery factor is introduced to correct the life expectancy of TOPIS again. Lastly, a practical case study of an operating transformer has been undertaken, in which the failure rate curve after introducing dynamic corrections can be obtained for the reliability assessment of this transformer. The curve shows a better ability of tracking the actual reliability level of transformer, thus verifying the validity of the proposed method and providing a new way for transformer reliability assessment. This contribution presents a novel model for the reliability assessment of TOPIS, in which the DGA data, as a source of information for the dynamic correction, is processed based on the grey target theory, thus the internal faults of power transformer can be diagnosed accurately as well as its life expectancy updated in time, ensuring that the dynamic assessment values can commendably track and reflect the actual operation state of the power transformers.

The state of a transformer depends on many parameters, which should be taken into account to determine its actual condition. In recent years what is known as health indices of transformers has been defined, which is a practical tool to assess the overall status of these electrical devices. Data from field inspection, laboratory tests, and observations during operation of the transformer are combined. All of these result in an index that provides fairly objective and quantitative information as to the condition of the transformer [1]. The research leading to these results has received funding from multiple sources over years, but we would specifically like to acknowledge the support received in the later stages from the Spanish Plan Estatal de I+D under the grant agreement DPI2013-43897-P.

Generally, high-temperature superconducting coated conductors (CC) are hard to be quenched by local and transient disturbances during normal operation because of the high temperature margin and high heat capacity of the conductor. However, the CCs still have possibilities of unexpected quenches originated by the appearance of local defects due to repeated mechanical stresses, and by temperature rise of the long part of the CCs due to malfunction of the cryogenic system, for example. In this work, the hot spot temperature of a CC with copper stabilizer during quench protection sequence is calculated by a numerical analysis for quenches by both of the origins mentioned above. The practical amount of the stabilizer is discussed not to over-protect but for a coil system to surely survive from sever damages caused by quenches considering quench origins.