Oil-immersed Distribution Transformers Research Articles

Multi-objective design optimization of hermetically sealed core-type distribution transformer considering current harmonics of power grid using NSGA III

In this paper, the design optimization of hermetically sealed oil-immersed distribution transformers is studied. For the first time in the design of this type of transformer, harmonics of the power grid affecting the transformer design, along with all design variables, are included, and their boundaries suitable for the production line are determined. The design probability (search space) for a total of 21 design variables is 1.32×1025. The Brute Force method is not a time-efficient approach to finding the optimal result in this search space. Due to the mixed integer nonlinear programming (MINLP) nature of the transformer design problem, heuristic optimization algorithms are selected because of their shorter solution time and near-optimal results. Considering the principle of the “No Free Lunch” theorem, extensive evaluations were conducted on various heuristic algorithms to identify the most effective ones for addressing the transformer design problem. The most successful algorithms for solving the problem were identified after thorough evaluation, considering three distinct scenarios within a multi-objective optimization framework. These algorithms are namely MOEA/D, MOGWO, MOWOA, and NSGA III. In this study, an optimization tool is developed for the design optimization of hermetically sealed distribution transformers, covering a range from 50 kVA to 3150 kVA and encompassing all design variables. The developed optimization program is fully compatible with the production line and can be easily adjusted to meet all national and international standards, such as IEC and IEEE, as well as customer specifications.

Load Losses and Short-Circuit Resistances of Distribution Transformers According to IEEE Standard C57.110

Load losses determine transformers’ efficiency and life, which are limited by overheating and deterioration of their elements. Since these losses can be characterized by short-circuit resistances, in this article, we have developed expressions for the short-circuit resistances of three-phase transformers according to IEEE Standard C57.110. Imposing the condition that these resistances must cause load losses of the transformer, two types of short-circuit resistance have been established: (1) the effective resistance of each phase (Rcc,z) and (2) the effective short-circuit resistance of the transformer (Rcc,ef). The first is closely related to the power loss distribution within the transformer. The second is just a mathematical parameter. Applying these resistances to the 630 kVA oil-immersed distribution transformer of a residential network, we have concluded that both types of resistances determine the total load losses of the transformer. However, only Rcc,z accurately provides the load losses in each phase. Rcc,ef can give rise to errors more significant than 16% in calculating these losses, depending on imbalances in the harmonic currents.

Transformer Fault Diagnosis Method based on PSO-GMNN Model

Background: Oil-immersed distribution transformer is an important power transmission and distribution equipment in the power system. If it fails, it will cause huge economic losses and safety hazards. It is of great significance to identify and diagnose its faults, find potential faults in time, and restore normal operation. Objective: To detect transformer fault, a transformer fault diagnosis method based on Graph Markov Neural Networks for Particle Swarm Optimization algorithm (PSO-GMNN) is proposed. Methods: Five common dissolved gases in transformer oil are used to construct a 22-dimensional feature set to be selected, and then the similarity between each feature vector is calculated by using Mahalanobis Distance. The graph structure is constructed with feature vectors as vertices and similarities as edges. Finally, the Particle Swarm Optimization algorithm is used to optimize the initial weights of Graph Markov Neural Networks, and then transformer fault diagnosis is realized. Results: The experiments are performed in the environment of Python 3.7, PyTorch 1.6.0, and the validity of the proposed method is verified by a comparative analysis of the detection accuracy between the proposed method and existing mainstream methods. Conclusion: A transformer fault diagnosis method based on Graph Markov Neural Networks for Particle Swarm Optimization algorithm is proposed to detect transformer fault, and the experimental results demonstrate the effectiveness and advantage of the proposed method.

Applications of Novel Heuristic Algorithms in Design Optimization of Energy-Efficient Distribution Transformer

Transformers are one of the crucial and expensive assets of a power grid. Reducing power losses in power and distribution transformers is important because it increases the efficiency of the transformer, which in turn reduces costs for the utility company and consumers. Losses in the transformer generate heat, which can reduce the lifespan of the transformer and require additional cooling. Additionally, reducing losses can help to decrease greenhouse gas emissions associated with the generation of electricity. This study presents an optimization method for transformer design problem using variables that have a great impact on the performance of a transformer. Due to the non-convex nature of the transformer design problems, the empirical methods fail to find the optimal solution and the design process is very tedious and time-consuming. Considering No Free Lunch (NFL) theorem, the design problem is solved using four novel heuristic optimization algorithms, the Firefly Optimization Algorithm (FA), Arithmetic Optimization Algorithm (AOA), Grey Wolf Optimization Algorithm (GWO), and Artificial Gorilla Troops Optimizer Algorithm (GTO) and the results are compared to an already manufactured 1000 kVA eco-friendly distribution transformer using the empirical methods. The outcome of the optimization shows that the suggested method along with the algorithms mentioned leads to a notable decrease in power losses by up to 3.5%, and a reduction in transformer weight by up to 8.3%. This leads to an increase in efficiency, decreased costs for materials, longer lifespan and a reduction in emissions. The developed model is capable of optimally designing oil-immersed distribution transformers with different power ratings and voltage levels.

Transformers Improvement and Environment Conservation by Using Synthetic Esters in Egypt

Distribution transformer (DT) is a crucial component in power systems as it exchanges energies between different voltage levels or between utility grid and DC microgrids. Nevertheless, the operation of an oil-immersed DT is limited by the thermal and electrical capabilities of the internal insulating liquid. This paper aims to raise the efficiency of distribution transformers and preserve the environment by using a biodegradable insulating liquid instead of the conventional mineral insulating oil (MIO). This work examines the Egyptian case, where a real distribution network located in middle Egypt is selected as a pilot project. Study and analysis of the status que of the insulation system inside DTs are done with the aid of fault-tree analysis. The deficiency of the insulation system is confirmed by conducting an electronic survey of 100 expert participants. The most appropriate solution among three different alternatives is confirmed using the weighting and ranking method. The best choice suitable for the selected area is the substitution of MIO by synthetic ester (SE). The technical and environmental advantages achieved by the presented solution are discussed. The feasibility studies have proven that the solution is positively acceptable in all aspects. An execution plan is established for the application of proposed solution on the selected Egyptian distribution network.

Influence of Load Factors on Distribution Transformer Noise

Theoretical relations between load factors and distribution transformer noise are analysed. A 10kV/400kVA three-phase oil-immersed distribution transformer is used for sound pressure level test in various load conditions including various load ratios, unbalanced loads and power factors. The sound pressure levels of distribution transformer in different load conditions are compared and analysed. The results can be referenced for the field noise and vibration control of distribution power transformers.

The Influence of Load on the Vibration and Noise Characteristics of Transformer

In order to further understand and grasp the impact of load on the vibration and noise characteristics of the transformer, this article analyzes the impact of load factors, power factor, harmonic current, three-phase unbalance and other load factors on transformer vibration and noise from the perspective of transformer vibration mechanism. A 10kV/200kVA three-phase oil-immersed distribution transformer was used as the object. Experiments were conducted to study the changes in the spectrum distribution, noise intensity and A-weighted sound pressure level of the transformer vibration and noise under the influence of different load factors. The results show that: when the frequency increases, the amplitude of the 100Hz fundamental frequency in the vibration noise signal increases, and the noise level increases accordingly; when the power factor increases, the amplitude of the odd frequency components in the vibration noise signal gradually decreases with the increase of the power factor. There is no obvious fluctuation in amplitude except 100Hz. When the harmonic current and the three-phase are unbalanced, the spectral components become complicated and accompanied by a large number of odd-order frequency multiplication components. With the increase of harmonic content, the amplitude of vibration noise signal and A-weighted sound pressure level increase significantly; the degree of unbalance and the occurrence of unbalance have a greater impact on the amplitude of vibration noise signal and A-weighted sound pressure level. The research in this paper provides a reference for the noise suppression of power equipment and the fault diagnosis technology based on vibration and noise signals.

Empirical Thermal Investigation of Oil–Immersed Distribution Transformer under Various Loading Conditions

Empirical Thermal Investigation of Oil–Immersed Distribution Transformer under Various Loading Conditions

Remote monitoring and alert system of HV transformer based on FMEA

This paper presents a technique to measure and collect maintenance data for remote monitor of high voltage transformer. The technique installs field instruments to measure winding temperature, cooling-oil temperature, inner pressure, electrical power, and so on. IoT2040 is applied for acquisition (DAQ), processing unit and smart gateway. It converts field data into information that enables for real time monitoring and preventive maintenance applications. This technique can transform time-based maintenance to condition-based maintenance. In addition, the proposed script functions are created based on failure modes and effects analysis (FMEA) to identify alarm and alert conditions. Consideration alarm-referenced parameters that are diagnostic, performance/efficiency analysis relate to operation or communication conditions also assign by script functions. The relevant data from IoT2040 can be transmitted to the local computer as well as a remote-mobile devices running the dashboard with Ubidots server. Ubidots server is responsible for HMI and delivering specific alarm and alert services to the user. Users can access for remote monitoring by smart phone, tablet, laptop, and PC. The experiment performs by simulation with 3 phase Oil immersed distribution transformer. Electrical specification is 50 Hz 250 kVA, 22 kV, 400/230 V. The results shown the assigned data, dashboard, and notices message that notices relate the FMEA scripts. The technique provides early warning detection of transformer statuses that make opportunity to take corrective action to prevent failure.

Thermal behavior investigation of installation orientation and color effect on distribution transformers using E-TRM method and its effect on loading

The importance of the distribution network is not overlooked by anyone. The transformer is one of the key equipment in this network. Therefore, great care and attention are needed in its design, maintenance and operation. Most of the oil-immersed distribution transformers are operated under solar radiation conditions. However, increasing the oil temperature due to solar radiation is not considered in their design. This increases the oil temperature above the design temperature value and thus reduces the life of the transformer. In this paper, due to the lack of specified equations for solar energy absorption by the fins and tank of the transformer, a novel method and equation are proposed for the calculation of the transformer solar radiation absorption amount. As well as, the effect of orientation on the corrugated tank distribution transformers oil temperature is investigated using the Electro-Thermal Resistance Model (E-TRM). For this purpose, two identical transformers with different orientations are tested experimentally and the results are compared and verified with the numerical results. The transformer tank color is one of the effective factors of solar radiation absorption. Depending on the absorption and emission rates, the effect of the different colors of the transformer tank on the oil temperature in different loading is investigated in this paper. The results show that the use of bright colors in comparison with dark colors can lower the oil temperature by about 3 °C on the rated loading of the transformer. In order to consider the effect of solar radiation on the transformer, the modified ambient temperature is introduced for the design of the transformer. Finally, the effect of transformer operation under solar radiation and with different colors is investigated and transformer loading de-rating is proposed by a novel equation.

Indoor distribution transformers oil temperature prediction using new electro‐thermal resistance model and normal cyclic overloading strategy: an experimental case study

In the energy distribution networks, the most important and valuable equipment is oil-immersed distribution transformers. Besides, due to the key role of these transformers and their multiplicity, their lifetime monitoring is inevitable. The life of a transformer depends on the weakest solid insulation material (i.e. paper insulation). On the other hand, monitoring the transformer insulation status requires accurate information to be available about the oil temperature at every moment. Therefore, it is important to control and predict the oil temperature rise in the transformer. In this study, a new model based on fundamental heat transfer theory is proposed for thermal behaviour prediction of top oil of indoor distribution transformers using the concept of thermal resistance, namely electro-thermal resistance model (E-TRM). In E-TRM, the thermal resistance network is formed by following three-dimensional heat transfer path and assigning thermal resistance to each path. To evaluate the proposed E-TRM, the results of this model are verified with experimental results. Moreover, the E-TRM is used to predict the thermal behaviour of the indoor transformer in the overloading condition. At the end, the transformer loss of life is estimated based on the oil temperature and a normal cyclic overloading strategy is presented for overloading management.

Study of winding vibration and transmission characteristics of three-phase oil-immersed distribution transformer based on FEA

In this paper, the magnetic-structure-acoustic multi-physical field model of S13-M400/10 distribution transformer is established through the FEA software. The harmonic response analysis method is used to study the winding vibration and transmission characteristics of the transformer. The simulation results show that the flux leakage distribution of windings on each core column is mainly determined by the current flowing through these windings. The radial and axial acceleration distributions of the windings are U shape and M shape respectively along the winding height. The acceleration of B phase windings is smaller than that of A and C phase windings. The vibration of the oil tank surface is concentrated in its middle and lower part. The tank side vibration is mainly affected by the vibration of the nearest phase windings, while the tank front vibration is affected by the vibration of the three-phase windings together. This study is of great significance for further studies of the vibration characteristics of the transformer under unbalanced load and proposing the vibration reduction and noise reduction measures for the distribution transformer.

CO2 footprint for distribution oil immersed transformers according to ISO 14067:2018

In the last few decades, climate change and the global warming have emerged as important environmental issues. The cause of global warming is the increase of greenhouse gas emissions (GHG). There are several greenhouse gases responsible for global warming: water vapor, carbon dioxide (CO2), methane, nitrous oxides, chlorofluorocarbons (CFCs) and others. They are mostly the result of the fossil fuels' combustion in cars, buildings, factories, and power plants. The gas responsible for the most of the global warming is carbon dioxide (CO2). This increase in the greenhouse gas emissions leads to a greater interest of the consumers, board management and stakeholders in the environmental impact of their activities, products and services.The verification of the Carbon Footprint of distribution oil immersed transformer, presented in this paper, was recognized as an opportunity for the company to understand its own environmental impact and to identify inefficiencies and opportunities within its business.Carbon Footprint of a Product (CFP) is a rather new term closely related to the greenhouse gas emissions. The CFP is considered as a total of the greenhouse emissions generated during the life cycle of a product – that is, from raw material acquisition or generation from natural resources to a final disposal. It is described within the standard ISO 14067:2018 Carbon footprint of products – Requirements and guidelines for quantification [1]. This standard belongs to the environmental series ISO 14000 and enables the organization to demonstrate its environmental responsibility.Life Cycle Assessment (LCA), as well as the Carbon Footprint of products together with environmental impact of the product, are shown in this paper in accordance with standard ISO 14067:2018. The LCA is a method for the quantification of the environmental impacts of individual products. It takes into account a complete life cycle, starting from a raw material production, until the product’s final disposal or materials’ recycling in accordance with ISO 14040 [2] and ISO 14044 [3]. Greenhouse gases are expressed in mass-based CO2 equivalents (CO2e), which is the unit of measurement in the ISO 14067:2018 standard. The functional unit in ISO 14067:2018 can be either a product or a service. In this paper, the functional unit was the product – oil immersed distribution transformer, in four product variations. The LCA scope used in the preparation of this study was "cradle to gate" – it covers the CFP from the acquisition of the raw materials ("cradle") up to dispatch from the factory ("gate").The objectives of product life cycle considerations in Končar D&ST Inc. are to reduce the use of natural resources and emissions to the environment, as well as to improve social performance at different stages of the product life cycle.By linking the economic and ecological dimension of the production, different aspects during realization of product in all phases of the life cycle come together. In this way company achieves cleaner products and processes, competitive advantage in the market and improved platform that will meet the needs of the changing business climate.Lifecycle thinking is based on the principles of reducing environmental impacts at the beginning of product creation, giving a wider picture of material and energy flow and ultimately environmental pollution prevention. These principles are organized in Končar D&ST Inc. internally by planning and introducing cleaner manufacturing processes, environmental protection management and eco-design.Incorporating ISO 14067:2018 into company business is recognized as an opportunity for transparent communication to interested parties, incorporating CO2 emissions into annual reports and as a baseline information for a first step towards managing carbon emissions.

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.

Simulation modeling study on short circuit ability of distribution transformer

Under short circuit condition, the oil immersed distribution transformer will endure combined electro-thermal stress, eventually lead to the mechanical damage of the inner winding of distribution transformer, therefore it is necessary to study the short circuit ability of the oil immersed distribution transformer. In this paper, the typical current waveform of the distribution transformer under the short-circuit condition is analyzed theoretically. The short circuit fault simulation model of distribution transformer is built on the MATLAB/Simulink simulation platform, the short circuit waveform of the single phase, double phase and three phase short circuit is obtained. Further on the ANSYS simulation platform, three dimensional solid modeling of the three-phase five column transformer is carried out, the harmonic and transient field are applied to analyze the magnetic field distribution of the key components in distribution transformer under the short circuit condition, the internal cause of large short-circuit force in the winding of the distribution transformer under the short circuit condition is analyzed to certain extent. The results of the modeling and simulation show that the three phase short circuit current is larger than the single-phase and bi-phase short circuit current. Its value is 1.45 times the normal running current, which is the gradual damping asymmetrical short-circuit current. Magnetic induction intensity is in-homogeneous in the circumferential direction of the core column, and the degree of in-homogeneity varies along height. The magnetic density distribution under the short circuit condition is more than 6 times as much as the the normal condition. From the point of view of simulation modeling, short circuit ability of the oil immersed distribution transformer is analyzed, distribution characteristics of short circuit current and magnetic field of oil immersed distribution transformer under short circuit condition have been obtained, the theoretical reference value of the state characteristics and protection measures of oil immersed distribution transformer under the overload condition can be provided.

Design and Monitoring of 1kva Distribution Transformer

Transformers are vital part of transmission and distribution system. Generally, the lifetime of the transformer varies from 40 to 50 years. Regular monitoring and maintenance must be done to increase its lifetime. The existing monitoring system can acquire, process, analyse and communicate the critical parameters viz. voltage, current, frequency, temperature, oil level, etc. and sends the values to a central hub and indicates the fault to the concerned person. These parameters are required by the operators to ensure reliable power delivery and to assist the day-to-day decision-making activities. A single phase, 1 KVA, 50 Hz, 230/115 V, oil-immersed distribution transformer is designed, and the above-mentioned parameters are monitored and displayed in mobile phones/personal computers. The values from the monitoring system is displayed in website or mobile application using cloud services. With the data available, various processes can be performed to obtain information. The proposed system can be installed in any available transformers with little modification in sensors. When a severe fault occurs secondary circuit-breaker is tripped thereby isolating the transformer and an official is alerted using a text message.

A Novel Model for Thermal Behavior Prediction of Oil-Immersed Distribution Transformers With Consideration of Solar Radiation

Monitoring the insulation status of a transformer requires the availability of accurate information of the oil temperature at any moment. Considering the importance of oil temperature prediction in oil-immersed transformers and its direct relation with the life of transformer, a novel model is presented in this paper using the concept of thermal resistance with consideration of solar radiation for expressing the heat transfer in distribution transformers. The results of the proposed model are compared and validated with experimental results. These results show that in the studied transformer and rated loading, solar radiation can increase the oil temperature by about 3.7 °C. In this paper, the thermal resistance model with solar radiation is used to predict the thermal behavior of the transformer in overloading condition. Finally, the transformer operation with/without consideration of solar radiation effect is studied and its impact on the transformer's loss of life due to the increase in oil temperature is investigated. In order to consider the effect of solar radiation on oil temperature, new equations using the concept of thermal resistance are presented to calculate the shadow surface created on the fin-folded transformers, and a novel equation is proposed for permissible loading of distribution transformers.

A Probabilistic Approach for Forecasting the Allowable Current of Oil-Immersed Transformers

The overall growth of electrical energy consumption and the spread of distributed generation pose severe problems to system planners and operators, mainly due to the difficulties in expanding and upgrading electrical distribution systems. These problems can be partially overcome through the smart operation of power system components. In particular, under the new smart grid paradigm, lines and transformers could be loaded beyond their nameplate rating in favorable thermal conditions, without loss of rated life or breakdown. This paper deals with the loading of oil-immersed distribution transformers, and it proposes a probabilistic approach based on the monitoring of electrical and environmental conditions. The approach consists in forecasting the predictive distribution of the transformer dynamic rating, and then in forecasting the transformer allowable current. The probabilistic approach takes into account the unavoidable uncertainties involved in the thermal modeling of the transformer; indeed, it selects the allowable current through an index that takes into account both the probability of the allowable current to be higher than the predicted dynamic rating and the corresponding expected load curtailment. Numerical applications are performed on real data to evaluate the effectiveness of the proposed procedure.

Fem CFD analysis of air flow in kiosk substation with the oil immersed distribution transformer

In practice of loading of oil-immersed distribution transformers, there is a need to have lumped thermal model, requiring no big computational resources and computational time. One such model is presented in international transformer loading guide (IEC 60076-7), where heat transfer inside the transformer is modeled. In case of indoor transformer operation, this model does not consider transient thermal phenomena in the room. We developed a lumped model that includes heat transfer in the transformer room. In scope of the research, we also built FEM CFD (finite element method, computational fluid dynamics) model of air flow and heat transfer. The purpose of FEM CFD was to make a better insight into air flow, i.e. to study the simplifications introduced in lumped model and suggest potential improvements. This paper presents results achieved with FEM CFD. The considered case was the transformer with natural oil and natural air flow (ONAN).

Design of Transformer With High-Permeability Ferromagnetic Core and Strengthened Windings for Short-Circuit Condition

This paper provides the design of 1 MVA three-phase oil-immersed distribution transformers considering short-circuit testing (SCT) and its impact on the windings. To maintain the transformer function after the SCT, only an impedance variation within 5% is allowed. Therefore, in conjunction with the particle swarm optimization (PSO), a simulation-based optimal approach is developed for the design of the distribution transformers. Finite-element analysis is used to work with the PSO for the calculation of flux densities, costs, core losses, and magnetostriction variations for the transformers under a prescribed noise level. Three transformer prototypes are then built using two types of amorphous cores and a conventional silicon steel core, respectively. The performance after the SCT is evaluated for the prototypes constructed. From the test results, it is found that the amorphous core is suitable for transformers in terms of lower noise level, core loss, and magnetostriction variation.