A comparative between IEEE and EN in the transformer derating when supplying nonsinusoidal load current. A practical case

Nowadays, power quality is a challenge for the distribution companies since the new energy policies are directed to a distributed generation system with power electronic based technologies. The reduction of distribution transformers capability when supplying nonsinusoidal load currents has a major impact within capacity reduction in distribution networks produced by technical losses. IEEE Std C57.110-2018, EN- 50464-3 and EN-50541-2 define procedures to derate transformers when supplying nonsinusoidal load currents. The aim of this paper is to compare these procedures through a real case distribution transformer that suffers problems due to high levels of current distortion.This research was funded by the “Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación” grant number “RTC-2017-6782-3”, the European Union FEDER funds with name “LOcalización de averías, monitorización de estado y Control en redes de bAja TEnsión—LOCATE” and the Horizon 2020 Program by the European Comision with project reference No 864579, H2020-LC-SC3-2019-ES-SCC

Impact of unbalanced harmonic loads towards winding temperature rise using FEM modeling

This paper investigates the hot spot temperature of transformer thermal model due to unbalanced harmonic loads from the network. The finite element method has been used to solve the coupling multiphysic for heat transfer in solid and fluid. All material properties in the model were been took into consideration such as copper as the coil material, iron as the core material and transformer oil as the coolant material for the transformer. The transient study on the model has been set for 1minutes using 30 degree celcius as the ambient temperature reference. The simulation hot spot temperature result has been compared for rated load (without harmonic) versus the unbalanced load (with harmonic) which shown in 2D regime. It can be clearly seen the significant increment of the hotspot temperature of the transformer from the rated load to the unbalanced harmonic load. The result has successfully shows the detection of the prospect failure of the transformer due to the harmonic current load in a form of winding loss that contributes to the hotspot temperature of the transformer

A New Design Of Three Phase Transformer Under Nonlinear Load Condition

Usage of nonlinear loads such as electronic device causes current at power distribution system to be distorted and contains harmonic. Effect of current harmonic is overheating of transformer at power distribution system. Overheating is caused by the increase of copper power loss at winding wire and core power loss (hysteresis and eddy current). As result insulation is degraded and risk of permanent malfunction at transformer (burn). Existing solutions regarding this problem is by reducing and increasing transformer capacity and the reduce of transformer loading. This gives bigger area to sustain effect of current harmonic. This thesis proposes a new design three phase transformer without changing of capacity. This can be achieved by resizing of winding wire and core. This transformer is specially design for nonlinear loading with current harmonic content (THDi) of 40%. Resizing method is performed at transformer material of winding wire and magnetic core in order to sustain the additional loss caused by current harmonic. It also reduces copper loss at winding wire and hysteresis loss at transformer core. Resizing technique is based on the determination of sizing factor with the function of THDi that is proportion to rated transformer operating temperature. It is the ratio between transformer operating temperatures under nonlinear loading. Experimental result on a three phase 2 kVA, 415V, 50Hz transformer yields sizing factor of 0.012 and 0.075 for winding wire and core respectively By utilizing the determined sizing factor, a new transformer is designed with winding wire AWG 19 and core with dimension 1358cm2. It is able to sustain additional transformer power loss caused by current harmonic as much 40% THDi at rated operating temperature 55°C. This design method can be improved by considering selection of material with higher permeability to the extent design dimension of transformer is made smaller (more economical)

Coupled electromagnetic and thermal analysis of electric machines

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe actual trend of the design process of electric machines is oriented to specific requirements of the application and is no longer based in a standard structure. From this point of view, the design procedure of electric machines became a multidisciplinary process, involving electromagnetic, thermal, and mechanical modelling in a highly iterative process between the different physics fields. This dissertation deals with the design process of electric machines, proposing a coupling methodology for the electromagnetic and thermal models which are interrelated. The electromagnetic model establishes the main losses in electric machines: iron and resistive losses. These losses are, in turn, the main heat sources, responsible for heating and temperature distribution, i.e., the object of the thermal analysis, which affects recursively the losses, due to parameter’ dependency on temperature. Also, the machine temperature is crucial to maintain the lifetime of the machine. So, the coupled analysis is mandatory to achieve the nowadays requirements of higher energy efficiency and power density and cost reduction. Also, the coupled analysis enables optimization without the need to build several prototypes, making this process more time and cost-efficiency. Despite the temperature importance in electric machines, the thermal model was overlooked over the years. However, it has been receiving more attention in the past years. In this work, the thermal modelling process is handled analytically and numerically through finite element analysis (FEA), which is also used to obtain the electromagnetic model. The modelling processes detailed during this work are applied into a case study of a single-phase transformer with the rated power of 1 kW. The numerical models were developed in the Ansys software suite, being the electromagnetic model developed in Ansys Maxwell while the thermal model has developed in Ansys Mechanical. At last, the coupling between the electromagnetic and thermal models was accomplished in Ansys Workbench. The results obtained from the models are compared and validated with the experimental measurements of the losses and temperatures.A tendência atual do processo de projeto de máquinas elétricas é orientada para requisitos específicos de sua aplicação e não é mais baseada em uma estrutura padrão. Deste ponto de vista, o procedimento de projeto de máquinas elétricas tornou-se um processo multidisciplinar, envolvendo modelagem eletromagnética, térmica e mecânica em um processo altamente iterativo entre os diferentes campos da física. Esta dissertação trata do processo de projeto de máquinas elétricas, propondo uma metodologia de acoplamento dos modelos eletromagnético e térmico que se inter-relacionam. O modelo eletromagnético estabelece as principais perdas em máquinas elétricas: perdas de ferro e resistivas. Essas perdas são, por sua vez, as principais fontes de calor, responsáveis pelo aquecimento e distribuição de temperatura, ou seja, o objeto da análise térmica, que afeta recursivamente as perdas, pois os parâmetros são dependentes da temperatura. Além disso, a temperatura da máquina é crucial para manter a vida útil da máquina. Assim, a análise acoplada é obrigatória para atender aos requisitos atuais de maior eficiência energética e densidade de potência e redução de custos.Além disso, a análise acoplada possibilita a otimização sem a necessidade de construção de vários protótipos, tornando este processo mais eficiente em termos de tempo e custos. Apesar da importância da temperatura nas máquinas elétricas, o modelo térmico foi negligenciado ao longo dos anos. No entanto, tem recebido mais atenção nos últimos anos. Neste trabalho, o processo de modelagem térmica é tratado analiticamente e numericamente por meio da análise de elementos finitos (FEA), que também é utilizada para obter o modelo eletromagnético. Os processos de modelagem detalhados durante este trabalho são aplicados em um estudo de caso de um transformador monofásico com potência nominal de 1 kW. Os modelos numéricos foram desenvolvidos no pacote de software Ansys, sendo o modelo eletromagnético desenvolvido no Ansys Maxwell enquanto o modelo térmico foi desenvolvido no Ansys Mechanical. Por fim, o acoplamento entre os modelos eletromagnético e térmico foi realizado no Ansys Workbench. Os resultados obtidos com os modelos são comparados e validados com as medições experimentais das perdas e temperaturas

Evaluation of power system harmonic effects on transformers : hot spot calculation and loss of life estimation

The significance of harmonics in power systems has increased substantially due to the use of solid state controlled loads and other high frequency producing devices. An important consideration when evaluating the impact of harmonics is their effect on power system components and loads. Transformers are major components in power systems. The increased losses due to harmonic distortion can cause excessive winding loss and hence abnormal temperature rise. Existing standards give a procedure to determine the capability of an existing transformer subject to non-sinusoidal load currents based on conservative assumptions. The eddy current loss generated by the electromagnetic field is assumed to vary with the square of the rms current and the square of the frequency (harmonic order h). Actually, due to skin effect, the electromagnetic flux may not totally penetrate the strands in the winding at high frequencies. In addition, the temperature rise due to harmonics is estimated based on constant harmonic load currents and the average daily or monthly temperatures to which a transformer would be subjected while in service. It is the purpose of this research effort to quantify the increased winding losses due to harmonics and the corresponding temperature rise in transformers. This is accomplished using a 2-D FEM model adapted for winding loss calculation. A corrected harmonic loss factor that considers conductor skin effect is proposed and verified by measurements. Thermal dynamic models are investigated and modified to consider a time varying distorted load cycle. The increased temperature is used with an industry accepted insulation loss of life formula to evaluate a transformer's capability.reviewe

An Analysis of Harmonic Heating in Smart Buildings and Distribution Network Implications with Increasing Non-linear (Domestic) Load and Embedded Generation

Harmonic distortion is generally not taken into account within domestic installations and the associated wiring systems, as its potential is considered sufficiently small to be neglected. Standards to limit harmonic manifestations in the low voltage (LV) network are available, but these can be breached as a consequence of advancements in power electronics in some modern household devices contributing higher levels of harmonic distortion than permitted. While these devices individually might not be considered serious in terms of system level harmonic distortion manifestations, electrical equipment failures and insulation failures - increasingly being derived from harmonic cable heating - suggest a different story. A 10% increase in THD in a circuit will result in an increase of 10% in cable heat. Recently, attempts have been made to offer harmonic derating factors for building electrical circuit design in BS7671, but this approach currently prioritizes large power devices. This article explores the need for harmonic considerations during the design stage of electrical services engineering projects. Best practice suggestions, in the context of the dissemination of heat caused by harmonics related to household load deployments/configurations, are also provided based on the analysis conducted with real household data. This is further extended to a practical distribution network where the effect of harmonic heating at the network level is explored. The results suggest that the harmonics in the distribution network can amass to cause a cumulative effect on the network. Furthermore, it can be observed from the results that in a distribution network containing (domestic) solar photo voltaic (PV) systems, the harmonic heating issue can be reduced. This benefit is not without consequence however, as increasing PV penetration does not reduce the harmonic content of the overall system and therefore presents a further concern that may need to be addressed in due time

Multi-objective optimization of power electronic converters

L'abstract è presente nell'allegato / the abstract is in the attachmen

Assymmetry in distribution systems: causes, harmful effects and remedies

ABSTRACT: Current and voltage asymmetry denigrates the power system performance. The current asymmetry reduces efficiency, productivity and profits at the generation, transmission and distribution of electric energy. Voltage asymmetry reduces efficiency, productivity and profits at the consumption/utilization level. There are a lot of conference and journal papers on the subject of voltage and current asymmetry, however, the information is scattered over a large number of journals and conferences and published over several years. Therefore, the thesis provides a comprehensive compilation of all possible published information on current and voltage asymmetry in the electrical power systems. Published information on sources of asymmetry, its propagation, negative effects upon transmission and customer equipment and possible remedies are compiled, discussed and analyzed in this thesis. This is done with respect to the voltage asymmetry and current asymmetry, as well as their mutual interaction. Some situations related to the voltage and current asymmetry are modeled in this thesis using the Electrical Transient Analyzer Program (ETAP) software. Due to the economics and efficiency of transmission, distribution and load diversity such as single-phase, two-phase and three-phase utilization, asymmetric current and voltage is an inherent feature in the distribution system. Therefore it has to be mitigated. The thesis discusses methods aimed at reducing the current and voltage asymmetry in the distribution system. Some of the sources of these methods are based on the Current Physical Component (CPC) power theory