Single-phase Distribution Transformers Research Articles

Estimation of the Equivalent Circuit Parameters in Transformers Using Evolutionary Algorithms

The conventional methods of parameter estimation in transformers, such as the open-circuit and short-circuit tests, are not always available, especially when the transformer is already in operation and its disconnection is impossible. Therefore, alternative (non-interruptive) methods of parameter estimation have become of great importance. In this work, no-interruption, transformer equivalent circuit parameter estimation is presented using the following metaheuristic optimization methods: the genetic algorithm (GA), particle swarm optimization (PSO) and the gravitational search algorithm (GSA). These algorithms provide a maximum average error of 12%, which is twice as better as results found in the literature for estimation of the equivalent circuit parameters in transformers at a frequency of 50 Hz. This demonstrates that the proposed GA, PSO and GSA metaheuristic optimization methods can be applied to estimate the equivalent circuit parameters of single-phase distribution and power transformers with a reasonable degree of accuracy.

Follow-Up Model to Evaluate Failure Factors of Single-Phase Distribution Transformers in High Environmental Pollution Zones

Single-phase distribution transformers are commonly installed in outdoor distribution networks to supply electricity to final users. Utilities are used to receive abnormal operating reports related to typical failures that negatively affect the reliability and security indicators. Therefore, a follow-up model is proposed in this paper to evaluate the failure factors of distribution transformers installed in high environmental pollution zones. The results show that the main factors that cause failures are overload, overvoltage, overcurrent, moisture, hot spots, manufacturing process, and lack of technical knowledge. Furthermore, all those factors are presented in a typical case using time-lines diagrams to characterize the main failures. Finally, hot spots, overloads, and unauthorized connections are the most critical failure factors identified in the research. According to the statistical analysis, those failures could occur 16 days after installing the transformer. The follow-up model presented in this research can characterize the main failures presented in outdoor distribution transformers.

Sine-cosine optimization approach applied to the parametric estimation in single-phase transformers by considering voltage and current measures

In this article, a combinatorial optimization approach for estimating the electrical parameters in single-phase distribution transformers by considering voltage and current measures is presented. A nonlinear programming model was formulated to represent the parametric estimation problem. This mathematical optimization model was developed by applying Kirchhoff’s laws to the equivalent electric circuit of the transformer. To solve the NLP model is employed the sine-cosine algorithm, which corresponds to a combinatorial optimization methodology from the family of metaheuristics that has the ability for finding good solutions with minimum computational requirements, easily implementable at any programming language. Numerical results show that the parametric estimation in the transformers using the proposed NLP model represents the electrical behavior of these devices adequately, considering different load scenarios. All the simulations were carried out using MATLAB software and compared with the GAMS optimization package.

Synthesis of Load and Feeder Models Using Point on Wave Measurement Data

This paper describes a novel method to synthesize load and feeder models, by estimating the load composition and the load parameters, using instantaneous voltage and current measurements, obtained at the distribution level, from disturbance events. A novel feeder model structure has been proposed in this work comprising of single-phase loads, three-phase loads, impedance loads, distribution transformers and distribution line segments. The load composition of the proposed feeder models and the motor load parameters are determined using a non-linear least squares algorithm integrated with an electromagnetic transient (EMT) analysis tool PSCAD. The efficacy of the proposed algorithm is examined for feeders at different physical locations and with distinctly varied load characteristics. Using this approach, parameters of the motor loads have been obtained within a fixed set of bounded values for each corresponding parameter. The ability of the proposed feeder and load models to capture severe fault induced delayed voltage recovery events (FIDVR) has also been discussed here.

GSM BASED SINGLE PHASE DISTRIBUTION TRANSFORMER MONITORING AND CONTROL

This paper is about prevention of Faults in the single phase distribution transformers. Generally distributing transformer many factors are present but some factors are very important to protect distributing transformer. Temperature sensor, ultrasonic sensor, voltage sensor, current sensor are used in this work, to measure the readings. These sensors are to sense particular parameters on the transformer. This system is fully based on embedded through GSM. The information is send through particular substation. Some unreachable places, It is very difficult to measure the parameters. This system is very useful to measure and control the single phase distribution transformer. This system is very helpful for electricity board. We can design and implement the single phase distribution transformer at mini prototype model. Large size capacity of 3 phase distribution transformer can be implemented in the future the model. Each and every distribution transformer data’s will collect through this system then fault can be identify and rectify it. Open source Arduino platform can be used to integrate all the sensors.

Procedure to Evaluate the Impact in Distribution Single Phase Transformers Due to Insertion of New Nonlinear Load Which Changes Daily Demand Graphs

Power electronic development determines the introduction of nonlinear devices in electric power systems. Introduction of nonlinear devices increase current harmonics in transmission and distribution power systems. Distribution transformers and feeders increase power losses and their nominal parameters are reduced. The present work introduces a procedure to evaluate maximum permissible load in single phase distribution transformers with the introduction of a new type of nonlinear load which changes daily demand graphs.

Measurement of the No-Load Characteristics of Single-Phase Transformer Using an Improved Low-Frequency Method

A large-capacity nominal-frequency (NF) power supply is required to measure the no-load characteristics of transformers, including the no-load loss, excitation current, and no-load current harmonic content for field and factory tests. The traditional NF method uses bulky test equipment and requires a highly complex test operation. This paper proposes an improved low-frequency (LF) method to reduce the capacity requirement of the testing power supply and make the test equipment portable. In this method, the core loss at LFs is first calculated by applying sinusoidal voltages at several LFs. The resultant core loss at LFs is then converted to core loss at NF based on the core loss separation and orthogonal least squares method. Finally, the excitation current, no-load loss and excitation voltage are determined by a corresponding eddy current compensation algorithm. In addition, experiments were conducted on a single-phase distribution transformer. The experimental results confirm that, compared to the traditional NF test, the proposed method possesses a similar measuring accuracy but reduces the capacity requirement of the testing power supply.

Reduction of Three-Phase Voltage Unbalance Subject to Special Winding Connections of Two Single-Phase Distribution Transformers of a Microgrid System Using a Designed D-STATCOM Controller

The U-V or V-V winding connections of two single-phase distribution transformers are widely utilized in distribution systems to deliver power to various three-phase and/or single-phase loads. Such special winding connections of distribution transformers can cause three-phase voltage unbalance in distributions systems, which could also lead to unexpected trip of ground relay, extra power losses on distribution-system lines, reduced operating efficiency of induction-motor loads, etc. This paper proposes a distribution static synchronous compensator (D-STATCOM) to effectively improve the voltage unbalance of a distribution system connected with a microgrid system. The studied microgrid system contains various renewable-energy resources, a diesel-engine generator, and three distribution transformers with U-V and/or V-V winding connections. The simulation results show that the proposed D-STATCOM with the designed controller can effectively reduce voltage unbalance of the distribution system connected with the studied microgrid system when the distribution transformers have U-V and/or V-V winding connections.

Estimation of Design Parameters of Single-Phase Distribution Transformers From Terminal Measurements

In this paper, a novel method is proposed for the estimation of the design parameters of single-phase distribution transformers using data acquired from terminal measurements along with nameplate data and external tank dimensions. Transformer parameters that can be measured from terminals, for example, leakage inductance, saturation inductance, and winding resistance, are considered first. These parameters are analytically correlated with the geometrical information of the transformer structure. A system of nonlinear equations is derived accordingly. Winding dimensions and the number of turns are computed with acceptable engineering accuracy. The core dimensions (including its cross-sectional area) are calculated using winding information. The obtained data can be utilized to develop white- or gray-box models to be used in the investigation of the thermal and/or electromagnetic behavior of power transformers as presented in several research studies published to date. Examples on laboratory and utility-grade transformers are shown for illustration and validation of the proposed design parameter estimation method.

Effect of a lossy dispersive ground on lightning overvoltages transferred to the low-voltage side of a single-phase distribution transformer

This paper presents a study of lightning overvoltages transferred to the low-voltage side of a 10kVA 7.967kV/240–120V single-phase distribution transformer considering dispersive ground effects in the medium-voltage distribution line terminated at its primary side. A two-port wideband model that is capable to represent the transformer behavior under different load conditions is considered. The medium-voltage distribution line is modeled using Marti’s transmission line model modified to include the variation with frequency of the ground resistivity and permittivity. Periodical grounding points are also modeled considering dispersive ground effects. Phase-neutral voltages transferred to the transformer secondary are calculated for direct lightning strikes at the medium-voltage line including insulation breakdown, surge arresters, and different load conditions. It is shown that the frequency variation of the ground resistivity and permittivity can significantly affect voltages transferred to the low-voltage side of the transformer if a high-resistivity soil is considered, depending on load conditions and on flashover occurrence. It is also shown that the importance of considering or neglecting frequency-dependent ground parameters on lightning overvoltages transferred to the secondary side of the transformer is minimized by the installation of a medium-voltage surge arrester at its primary side.

Analysis of the Maximum Inrush Current in the Otimal Design of a Single Phase Transformer

The main objective of this work is to design a single-phase distribution transformer core type involved, with the help of optimization techniques to minimize total losses (core and windings). The optimization algorithms used are the differential evolution and particle swarm. His performances and results are compared. Moreover, it is detailed the importance of a good estimate of inrush current in transformers projects, its interference in security systems and electric power system in general. The main parameters of the project, the core dimensions, total losses, the no-load current and the transient magnetization current are computed through Octave software. These values are used to determine the geometry of the active part of the transformer in order to simulate the magnitude of flux density in the transformer core and the losses through finite element method using FEMM (Finite Element Method Magnetics) software. It was through the results the effectiveness of the methodology used, with reducing losses, improving the efficiency and significant decrease of the Inrush current.

Método para determinar las pérdidas totales en transformadores de distribución a partir del porcentaje de carbono de la chapa de acero al silicio

Los transformadores son dispositivos eléctricos que se encargan de la distribución y manejo de la corriente eléctrica. En América Latina el reciclaje de la chapa de acero al silicio de los transformadores es muy común y por esta razón su construcción es de gran importancia debido hay que considerar las pérdidas que se pueden presentar por corrientes parásitas e histéresis magnética sobre todo cuando el equipo ha operado bajo condición de carga. Este artículo propone un novedoso método para determinar las pérdidas totales en los transformadores de distribución monofásicos de poste, analizando el porcentaje de carbono de la chapa de acero al silicio y sus características químicas. Este diagnóstico verifica las pérdidas en el hierro de forma proporcional al cuadrado de la inducción y frecuencia aplicando también la fórmula de Steinmentz con el fin de realizar diagnóstico y predicción de fallas. Los resultados obtenidos aunque presentan errores de aproximación son de gran utilidad para el diagnóstico y la reutilización de la chapa de acero al silicio, ya que los cambios en la micro estructura (tamaño de grano en escala nanométrica) o relación entre la calidad B-H son significativos, el aporte a los fabricantes y la industria en general es exegético, porque si son considerados los valores establecidos en la norma para los equipos operando bajo esta condición, se mejoran las condiciones del servicio en las redes de distribución y en consecuencia, la confiabilidad y/o mantenimientos en las empresas del sector eléctrico.

Harmonic Propagation from the Low Voltage Four-Wire Delta Systems

The electric networks for the distribution to low voltage costumers can be configured in different layouts. Two main approaches are used: the European system composed by three-phase distribution transformers or the North American system composed by single-phase distribution transformers and three-phase transformer banks of single-phase transformers. With respect to harmonic analysis, much more attention has been focused on the three-phase balanced systems arrangements than on the unbalanced four-wire delta system extensively used to supply low voltage loads of 120/240 V. Different authors have shown the three-phase power systems modeling on a phase-coordinates frame. However, the presence of significant asymmetries in the network forces the need of adding a new phase-coordinates model to represent the three-phase transformers banks of two or three single-phase transformers in its various connections. Several papers treat the use of harmonic analysis programs based on a phase-coordinates frame to study the Wye or Delta connected three-phase systems. However, the commonly used four-wire delta connected systems are not fully treated in literature. This paper presents a phase-coordinates model for the representation of the commonly used three-phase transformer banks of three or two single-phase transformers, and single-phase distribution transformers for the harmonic analysis of the four-wire delta connected systems. The harmonic analysis method based on the presented model is used to examine the characteristics of this kind of distribution system with respect to the penetration of harmonics currents from loads to the primary system.

Stability Design Criteria for Distribution Systems With Solid-State Transformers

Due to recent advancements in semiconductor technology, power-electronic converters for high-voltage, high-power, and high-frequency applications will soon be commercially available. The theoretical concept of a distribution solid-state transformer (SST) is not recent, but with the use of advanced electronic switches and control strategies, the SST may soon become a practical reality. In this paper, conventional single-phase distribution transformers are replaced by solid-state transformers in a distribution test system to investigate their interactive dynamics. Under certain circumstances, instabilities due to harmonic resonance are observed. A design criterion for a solid-state transformer during no-load conditions has been proposed in order to avoid instability using an impedance-based analysis. Analytical and simulation results are provided to support the proposed design approach.

Effects of magnetostriction and magnetic reluctances on magnetic properties of distribution transformers

This paper analyzes the causes of magnetic reluctance in silicon steel wound cores with multi step-lapped joint structures through the appropriate exploitation of simulated and experimental local flux distributions in an air-gapped core, to propose techniques that can enable the reduction of the resulting core loss and vibration. The magnetic magnetostriction forces in the lap-joint regions, constituting another significant source of permeability, can be controlled by rearranging the step-lapped joint structure. Then, the computed local flux distributions were compared with experimental data. Single-phase pad-mounted distribution transformers with a capacity of 167 kVA were used in this study. It is indicated that the multi-step lap joint can significantly reduce the core loss and exciting power by regulating the configuration of adjacent air-gapped distances. Finally, composite-core structures were also used to validate the reduction of magnetostriction, core loss, and vibrations, corresponding to single-phase distribution transformer.

NSGA-II phase balancing of primary distribution circuits by the reconnection of their circuit laterals and distribution transformers

The primary distribution circuits are unbalanced not only by the spread use of unbalanced three-phase transformer banks and single-phase distribution transformers, but also by the use of two-phase three-wire and single-phase two-wire circuit laterals. The unbalance of the phase currents produces two fundamental problems in the circuit: the energy losses in the primary conductors are increased and the presence of a high neutral current on normal operation make it difficult the detection of earth faults by the neutral over current relays. The present work implements an NSGA-II application for the phase balancing problem, which search for the minimal reconnection needed for the two-phase three-wire and the single-phase two-wire circuit laterals, as well as for the three-phase transformer banks and the single-phase distribution transformers, to minimize both: the energy losses and the maximum neutral current of the circuit. The successful performance of this application is achieved by the new definition of the set of independent variables, which permits the NSGA-II to optimize the selection of the elements to be reconnected. A test example with all the needed data is solved to shows the features of the presented approach.

Core lamination selection for distribution transformers based on sensitivity analysis

In this paper, the sensitivity analysis is used to select the core lamination thickness of single-phase distribution transformers rated from 5 to 50 kVA. Three different magnetic materials (M2, M3 and M4) with thicknesses of 0.18, 0.23 and 0.27 mm are considered. Transformer designs are compared based on the total owning cost as well as on the transformer bid price. The impact of the different laminations on total owning cost and bid price is calculated for a total of 144 transformers (72 for each criterion). All transformers fulfill all the operating and construction constraints. The paper considers the impact on core losses of the space factor (core-assembling pressure) and of the building factor and also describes how core losses are affected by core design parameters such as the number of laminations per step, air gap and overlap. It is concluded that for the analyzed power range, M3 lamination is the best choice since all of the studied cases have smaller bid price and 79% of the studied cases have lower total owning cost. This paper gives guidelines to select the appropriate thickness and can help transformer manufacturers to select the optimal thickness for distribution transformers.

Compensación Paralelo de Reactivos Durante la Prueba de Aptitud al Cortocircuito en Transformadores de Distribución

This article presents a strategy for using parallel reactive compensation with capacitors to increase the capacity of the short circuit test field at the Universidad del Valle. Transformers are key elements to maintain the electrical supply service. For that reason they must have an adequate capacity to withstand the mechanical, thermal and electrical stresses that occur during a short circuit. The High Voltage testing laboratory of the Universidad del Valle (Cali, Colombia), carries out short circuit tests for single phase distribution transformers up to 100kVA and for three phase transformers up to 300kVA. The short circuit withstand test at the laboratory is limited by the distribution network current capacity and the test can only be done at a fixed voltage, defined by the electrical network. The results show that parallel reactive compensation is a good alternative to reduce capacity requirements in short circuit tests.

Techno-economic Evaluation of Reduction of Low-voltage Bushings Diameter in Single-phase Distribution Transformers

The contributions of this article are the analysis and economic evaluation of the impact on tank wall losses of a diameter reduction of low-voltage bushings of pole-mounted single-phase distribution transformers. Finite element simulations of 5- to 167-kVA transformers were performed. The study was motivated when bushing manufacturers reduced diameter from 4.6 to 3.6 cm. Results show that when the diameter of low-voltage bushings is reduced, (i) load losses increase and (ii) total owning cost decreases for transformers up to 15 kVA and increases for transformers of 25–167 kVA. The insertion of non-magnetic material between bushing holes is also evaluated.

Optimal design of single-phase shell-type distribution transformers based on a multiple design method validated by measurements

This paper presents a method for the design of shell-type, single-phase distribution transformers to obtain the manufacturing specifications. The method is simple, efficient and accurate. By an exhaustive analysis, it is concluded that the obtained solution is the global optimum. The following constraints are imposed: excitation current, no-load losses, total losses, impedance and efficiency. The methodology of this paper requires only six input data: transformer rating, low voltage, high voltage, connection of low-voltage coil, connection of high-voltage coil, and frequency. These data are included in the transformer nameplate. In this paper, the minimization of the following four objective functions is considered: total owing cost, mass, total losses and material cost. The consideration of these four objective functions is implemented automatically by running the optimization algorithm four times without intervention of a designer. Consequently, transformer manufacturers save design man-hours and increase capacity. A design example on a 25 kVA transformer is presented for illustration. The optimized solutions of transformer design are validated with laboratory and process measurements.