Bora Alboyaci

Comparison of Power Loss and Magnetic Flux Distribution in Octagonal Wound Transformer Core Configurations

In this paper, various configurations of octagonal wound transformer core topology, which has previously proved advantages on conventional wound cores, are studied. Each configuration has different joint types and different placement of joint zones on the core. Magnetic flux distributions and power losses of each configuration are analyzed and compared. Comparisons are based on both 2D&3D finite element simulations and experimental studies. The results show that, joint types and their placements on the core cause local flux accumulations and dramatically affect power loss of the core.

A Novel Approach for Improvement of Power Swing Blocking and Deblocking Functions in Distance Relays

Power swing conditions in power systems make distance relays take the wrong breaker action in some cases. In this context, power swing blocking and power swing deblocking are two important functions in distance relays so as to distinguish power swing from a fault, which maintains stability of system and continuity of the power supply. In this paper, a sample estimation and error calculation method based on Taylor Series expansion is proposed for improving power swing detection performance of the relay. Performance of the method is compared with four conventional methods and a novel method in literature. Analyses are carried out in two systems: single machine-infinite bus system with parallel lines and 68-bus New England test — New York power system for fault, power swing, and fault during power swing scenarios. Simulations and performance analyses are carried out by using EMTDC/PSCAD and MATLAB, respectively. According to the results, when performances in correct operation, algorithm response times, clarity of outputs, and time passed for program execution on processor are considered, the proposed method has the best performance overall. It is found that by using the proposed method, distance relay performance in correct operation and speed for taking power swing blocking and deblocking actions are improved.

Improvement of power swing detection performance of a distance relay by using k-NN algorithm

In this paper, power swing detection is studied in terms of blocking distance relay responses which lead to wrong breaker operation. A new power swing detection method based on k-NN algorithm is proposed which uses areas of triangles constituted by phase angles of instantaneous power phasors calculated by Discrete Fourier Transform (DFT). Triangles corresponding to harmonic components from 1st to 9th are processed for generating the learning database. The performance of the method is compared with four conventional power swing detection methods on a test system in 30 cases for only symmetrical faults. The results show that the proposed method has better performance than the four conventional methods in total for the cases created in this work.

The Evaluation of Medium Voltage Motor`s Current and Voltage Harmonics during Loading

This paper presents the results of investigating harmonic levels on medium voltage motors at loading conditions in air separation plant. The essential results of the measurements of the medium voltage motor harmonics are summarized in the values for the total harmonic distortion (THD). Motors loading case is used to assess the current and voltage harmonic distortions. Proper system analysis is important when adding a new motor starting and controlling the equipment. With the result of the paper it is possible to suggest the most appropriate starting and control method. Two medium voltage motors of air separation unit measurement results and simulations are summarized. Both current and voltage harmonic distortions are fitted by using a linear and exponential regression model. The prediction of THD values can be used for this kind of process for future planning by utilities.

Elektrikli araç şarj istasyonu yüklerinin güvenilirlik indisleri üzerine etkilerinin incelenmesi

Bu calismada da elektrikli araclarin ve sarj istasyonu yuklerinin gelecek yillarda tum dunyada oldugu gibi ulkemizde de hizla artacagi dusuncesinden yola cikilarak olasiliksal yontemler ile elektrikli arac sarj istasyonlarinin dagitim sebekesinin guvenilirlik indislerine etkisi degerlendirilmistir. Bu calismanin; ulkemiz icin hem sebeke isletmesindeki cesitli risklerin daha detayli sekilde hesaplanabilmesi ve degerlendirilebilmesi, hem de elektrikli arac sarj istasyonlarinin potansiyel etkilerinin incelenebilmesi acisindan faydali olacagi degerlendirilmistir.

Yüksek verimli transformatörlerde buşing bağlantı noktalarında meydana gelen eddy akımı kayıplarının azaltılması

Bu calismada, transformatorlerin kazan kapagi uzerinde alcak gerilim sargilarinin baglanti uclari sebebiyle meydana gelen ve yuksek sicakliklara da neden olan eddy akimi kayiplari incelenmektedir. Bu kayiplarin azaltilmasi amaciyla kazan kapagi tasarimi manyetik ozellikli olmayan paslanmaz celik malzeme kullanilarak iyilestirilmektedir. Bu iyilestirme calismasi sirasinda imalat kosullari ve maliyet kriterleri de goz onunde tutulmaktadir. Farkli tasarimlar icin manyetik aki dagilimlari ve eddy akimi kayiplari uc boyutlu sonlu elemanlar yontemi yardimiyla analiz edilmis ve deneysel olarak da dogrulanmistir. Elde edilen sonuclar, kazan kapagi uzerinde alcak gerilim businglerinin baglanti yuzeyinin paslanmaz celikten imal edilen I-bicimli tek parca levha kullanilarak uretilmesi sonucunda kapak uzerinde meydana gelen guc kayiplarinin tamamina yakininin ortadan kaldirilabildigini gostermektedir.

A probabilistic approach for evaluation of electric vehicles' effects on distribution systems

With increasing number of electric vehicles and electric vehicle charge stations, the question that if existing infrastructure of distribution system will meet new requirements has gained great importance. Mutable load profiles of distribution system and charge stations makes engineering analyses more sophisticated. In this study, some probabilistic analyses are carried out in a local distribution system in order to demonstrate effects of electric vehicle loads on the system parameters. Analysis studies have been carried out on the model which is based on real data. Conventional and electric vehicle loads are forecasted in order to determine the effects of electric vehicle charge stations on voltage profile changes and transformer loading. Results are presented as comparative figures for different years studied.

Modelling and analysis of transformer using numerical and analytical methods

In this study, 1.25 MVA, 3-phase power transformer was analyzed using 2-dimensional and 3-dimensional finite element method (FEM) and analytical method. Leakage reactance, magnetic flux density, iron losses, energy, radial and axial force of the transformer were calculated using ANSYS Maxwell® software and analytical method. The prototype transformer was constructed based on the finite element method results. The numerical and analytical results of the different parameters of the transformer were also compared with the experimental results. Results show that finite element analysis method is the highly efficient method for the calculation of the different parameters of the transformer. The difference between the experimental and 3-dimensional finite element method was not more than 5%. This method can be helpful for the transformer designers in the initial stages of the transformer designing.

An artificial neural-net based method for predicting distribution transformer’s total harmonic distortions

This paper presents a new method for predicting distribution transformerpsilas total current and total voltage harmonic distortion with artificial neural network. The method is based on the backpropagation learning technique. This paper shows the proposed method is promising in total harmonic distortion prediction. For better system planning it is necessary to analyze and predict the behavior of harmonics. By predicted values system planners take an appropriate strategy to decrease significant harmonics in distribution systems.