G. B. Kumbhar

Analysis of Short-Circuit Performance of Split-Winding Transformer Using Coupled Field-Circuit Approach

Summary form only given. The split-winding arrangement requires special short circuit design considerations. During short circuit conditions, there is a considerable distortion of the leakage field, which in turn produces high axial short circuit forces. This paper deals with the computation and analysis of electromagnetic forces in windings of split-winding transformers. A nonlinear-transient field-circuit coupled finite element model is used to simulate the split-winding transformer. A 70 MVA, 3-phase, 220/6.9/6.9 kV split-winding transformer is modeled under pre-set and post-set short circuit test conditions. Under the pre-set condition, the transformer is analysed with one as well as both the LV windings short-circuited to compare the axial forces produced in the windings for these two cases. The results show that there is a considerable rise in the axial forces when one winding is short circuited as compared with the case when both windings are short-circuited. The effect of initial magnetization of core on axial short-circuit forces is calculated and discussed. It is also shown that even though post-set method eliminates inrush related problems there is not much respite in short circuit forces.

Applications of coupled field formulations to electrical machinery

Purpose – This paper aims to give a perspective about the variety of techniques which are available and are being further developed in the area of coupled field formulations, with selective bibliography and practical examples, to help postgraduate students, researchers and designers working in design or analysis of electrical machinery.Design/methodology/approach – This paper reviews the recent trends in coupled field formulations. The use of these formulations for designing and non‐destructive testing of electrical machinery is described, followed by their classifications, solutions and applications. Their advantages and shortcomings are discussed.Findings – The paper gives an overview of research, development and applications of coupled field formulations for electrical machinery based on more than 160 references. All landmark papers are classified. Practical engineering case studies are given which illustrate wide applicability of coupled field formulations.Research limitations/implications – Problems ...

Analysis of Sympathetic Inrush Phenomena in Transformers Using Coupled Field-Circuit Approach

Sympathetic inrush current phenomenon occurs when a transformer is switched on in a power system network containing other transformers which are already energized. In this paper, the phenomenon of sympathetic inrush current is investigated using nonlinear-transient field-circuit coupled finite element formulation. The cases of the transformers connected in parallel and in series have been considered. The results obtained for a 31.5 MVA, three-phase transformer are presented and discussed in detail. This work also includes the investigation of parameters affecting the magnitude and duration of sympathetic inrush phenomenon, such as series resistance, switching-on angle, residual flux density and load conditions. These analyses provide a sound theoretical basis for a thorough understanding of the phenomenon.

Reduction of Loss and Local Overheating in the Tank of a Current Transformer

Transformer manufacturers often use low carbon steel for oil tanks to cut down production costs. The low carbon steel tanks experience not only high eddy currents loss, but also suffer from localized overheating in the tank particularly in the vicinity of insulated terminals. A numerical analysis of the eddy current loss generated in the tank walls of a current transformer (CT) due to adjacent high-current carrying primary conductor is presented. A 3-D nonlinear-transient finite-element method was used to determine the eddy current loss. Estimated losses at rated and overload conditions are then compared with the measured ones; they are in good agreement. In order to reduce the tank loss and local overheating, three nonmagnetic inserts are proposed and their effectiveness is analyzed. These inserts yield about 25 to 40% reduction in the total loss in the CT compared to that without any insert. Results also indicate that these inserts may be used to obtain a significant reduction in the local overheating, thereby contributing to improved life and reliability of the CTs.

Analysis of Half-Turn Effect in Power Transformers Using Nonlinear-Transient FE Formulation

The half-turn effect is present in transformers if the winding leads are taken out from the different sides of the core. The result is an additional half-turn in one of the core windows in a single-phase transformer, which can create overfluxing of the core leading to excessive losses and temperature rises. This paper presents a methodology to analyze the half-turn effect in power transformers. A nonlinear field-circuit coupled model is used to simulate the half-turn effect; the magnetic field is modeled using the finite-element method. The results show that there is a considerable increase in the flux density values in the core during load loss test, and the increased core losses can be comparable to the values under the rated voltage condition. The results obtained by the proposed methodology are validated with the experimental test results on a single-phase 40-MVA autotransformer. The half-turn effect can be eliminated by taking both the leads from the same side of the core. However, in order to reduce insulation clearances, a few compensating turns are wound on the end limbs to eliminate the half-turn effect. The paper also reports the experimental and the simulation results with the compensating turns. Analysis of the high induced voltages in the unexcited windings of the other phases during the load-loss test on the middle phase of three-phase three-limb transformers is also reported. In the three-phase five-limb transformers, the effects of half-turns in the three phases are almost cancelled under the balanced load conditions; this paper highlights the possibility of the core saturation due to the half-turn effect under appreciable unbalanced load conditions

An Improved Finite Element Computational Scheme for Transient Field-Circuit Coupled Systems

Time stepping simulation of transient field-circuit coupled problems is a computation-intensive area. In general, finite element (FE) modeling and simulation of a large class of engineering applications require heavy computations that are often repetitive in nature. Any deeper insight into the dependence of the FE solution or its characterization may allow significant reduction of computational efforts. This paper illustrates the possibility of characterization of the time-varying FE solutions for transient field-circuit coupled problems. The characterization leads to a significantly smaller FE model and an improved modeling and simulation scheme for such problems. Construction of the reduced FE model for the field is illustrated, along with its coupling to a general external electric circuit. Relation of the proposed approach to the well-known substructural approach based on Schur Complements is discussed. Possibilities of further improvement of the numerical properties of the FE equations, possibly leading to improved convergence of iterative solutions, are indicated. Finally, extension of the approach to nonlinear field-circuit coupled problems is illustrated. Numerical simulations using the proposed approach for a typical electromagnetic system with solid bars connected to external circuit are presented. The results are compared to those from a commercial software, and a relative assessment of the computational effort involved in the proposed and conventional methods is also presented.

Incentive Driven Distributed Generation Planning with Renewable Energy Resources

Renewable DGs may not be economically viable due to the stochastic generation and huge capital investment, but are an inevitable choice for sustainable energy development and future pla ...

Partial Discharge Localization in a Power Transformer: Methods, Trends, and Future Research

ABSTRACT This paper presents a comprehensive review of various techniques of partial discharge (PD) localization. The technologies reviewed are acoustic, ultra-high frequency (UHF), optical, and electrical according to their chronological order of development. The paper outlines the distinctive acoustic and UHF sensors, along with the algorithm for the localization of PD source. Various digital signal processing and statistical techniques applied are likewise discussed. A substantial effort has been given to electrical methods since they represent the most active and current field of PD research. In this paper, the techniques of PD localization used so far are compared, and their advantages and limitations are pointed out. The challenges and trends in future research in PD localizations are also discussed. The review given in this paper will be useful to develop the future technologies for PD localization thereby avoiding insulation damage. Thus, this paper is intended to serve as a guide for the research on the localization of PD inside the transformer winding.

An integrated approach for power loss reduction in primary distribution system

Power loss reduction is issue of main concern to the network operators. Various techniques such as capacitor placement, network reconfiguration and DG placement are considered to minimize the distribution system losses. DG and capacitor placement in the presence of network reconfiguration may rejoice optimal benefit in terms of loss reduction, voltage improvement, network up-gradation cost deferral, etc. Therefore, in this paper, various combinations of methods for power loss reduction are considered. It is concluded that simultaneous placement and sizing of DG and capacitor in the presence of network reconfiguration is most optimal combination. The mixed integer non-linear optimization problem of simultaneous placement of DG and capacitor units in the presence of network reconfiguration is solved. Due to its non-convex nature, this Mixed Integer Non-Linear Programming (MINLP) problem is solved using Harmony Search algorithm. The proposed formulation is tested on IEEE 33-bus distribution system. Loss reduction with capacitor, DG and network reconfiguration is compared with the independent placement of DG, capacitor, and network reconfiguration options. Power loss reduction and flat voltage profile with lesser computational time proves the importance of integrated model.

Review on Volt/VAr Optimization and Control in Electric Distribution System

In smart grid environment, Volt/VAr Optimization (VVO) is receiving great attention among other energy efficient techniques. The main concept of VVO is to utilize various Volt/VAr Control (VVC) and supporting devices in an optimal way for the purpose of minimal losses and maximum energy savings. However the care has been taken so that power quality of end-use customer will not be affected while satisfying various system and operational constraints. Several techniques have been suggested for the solution of VVO problem. VVO/VVC methods are classified as analytical methods, numerical methods, heuristic approaches, and intelligent methods. Some practical VVO experiences are also reviewed. This paper presents an overview of various solution methods applied in VVO problem and future research trends in this area.