Yazar "Hocaoglu, Mehmet Hakan" seçeneğine göre listele

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    Earth Fault Protection Selectivity Issues on Reactance Earthed Distribution System
    (IEEE, 2022) Atsever, Mert Bekir; Karacasu, Ozgur; Hocaoglu, Mehmet Hakan
    Increase in power demand, green initiatives and regulatory requirements force system operators to adopt more complicated distribution system layout which are resulted in dissension from traditional distribution system practises. The main source of this complexity can be listed as; extensive application of embedded generation into distribution systems, different earthing practices, increasing percentage of underground cables and lastly, parallel feeders causing loop flows. One of the consequences of the increased complexity is malfunctioning in the protection systems namely; false tripping especially for the earth faults. Thus, conventional non-directional protection relays are, gradually, replaced with the directional ones in radial topology. However, directional protection is more expensive since requirement of additional measurement devices is imminent. Consequently, to facilitate cost effective protection system implementation, directional protection and non-directional protection performances should be investigated properly. Distribution system which earthed trough reactance may also suffer directional discrimination because of possibility of unintentional resonance between neutral reactor and cable capacitances. In this study, boundaries of directional and non-directional protections are investigated by taking into account neutral reactance, cable length and parallel feeder number. It is proposed that, a hybrid algorithm selection procedures based on system parameters should be undertaken for a successful and selective protection.
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    A faulty feeder selection method for distribution network with unintentional resonance in zero sequence circuit
    (Elsevier, 2023) Atsever, Mert Bekir; Hocaoglu, Mehmet Hakan
    Faulty feeder selection is a challenging task for distribution system operator due to the low earth fault current magnitudes in compensated networks. However, extensive cable usage, especially in metropolitan cities, causes unintentional resonance in the network earthed through inductance or grounding transformer. The unintentionally resonated networks are not designed like intentionally compensated networks where faulty feeder should be isolated in a predetermined time. There are transient zero sequence current based methods, particularly synthesized for compensated networks to identify faulty feeders. However, zero sequence-based faulty feeder selection methods have drawbacks in the presence of underground cables. Further, transient zero sequence current is prone to many parameters such as capacitive imbalance and fault resistance. In this study, a transient negative sequence current based faulty feeder selection method is proposed. The effectiveness of the proposed method is demonstrated in a simulated 151-node distribution network. EMTP simulations are carried out by considering different fault inception times, fault resistance and capacitive imbalance of the system. Results show that negative sequence current offers selective faulty feeder selection and no false trip is observed in a representative unintentionally resonating distribution network.
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    Minimization of Voltage Harmonic Distortion of Synchronous Generators under Non-Linear Loading via Modulated Field Current
    (MDPI, 2023) Karakaya, Oktay; Balci, Murat Erhan; Hocaoglu, Mehmet Hakan
    The synchronous generators (SGs) supplying non-linear loads have harmonically distorted terminal voltages. Hence, these distorted terminal voltages adversely affect the performance pa rameters of the supplied loads such as the power factor, current distortion, losses, and efficiency. To mitigate the harmonic voltages and currents, passive and active filters are generally employed. However, passive filters cause resonance problems, while active filters can cause high costs. On the other hand, in several recent studies to reduce the SG’s terminal voltage harmonic distortion, which depends on the constructional design under the no-loading condition, the conventional DC excitation current has been modulated with AC harmonic components. These field current modulation methods have high computational complexity, and require extra hardware for their implementation. In the present paper, firstly, for the reduction of the terminal voltage harmonic distortion of the SG under non-linear loading conditions, the validity of the field current modulation technique is investigated. The numerical results show that by using the field current modulation method, under rated loading conditions, the total harmonic distortion of the terminal voltage can be reduced from 18% to 11%. Secondly, to provide a computational efficient and low-cost tool for optimal field current modulation, which minimizes the terminal voltage harmonic distortion, an Artificial Neural Network (ANN)- based model is proposed. Finally, with the integration of ANSYS Maxwell, ANSYS Simplorer, and MATLAB/Simulink software, the implementation of the developed model is demonstrated for the construction of the optimally modulated field current.
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    Modelling, analysis, and improvement of energy consumption in data centres via demand side management
    (Elsevier, 2024) Takcı, Mehmet Türker; Gözel, Tuba; Hocaoglu, Mehmet Hakan
    The demand for data centers has increased in recent years due to the need for businesses to store, process, and manage vast quantities of data, as well as the swift advancements in information technology and digitalization. As more organizations adopt technologies such as artificial intelligence, big data analytics, cloud computing, and storage capacity, their requirements for computational power, rapid data access, and storage capacity grow. Furthermore, the significance of data centers has been further emphasized due to the growing prevalence of remote working options, online platforms, and other digital services. Data centers typically comprise infrastructure such as high-performance servers, data storage systems, network infrastructure, cooling systems, and power conversion systems. Particularly high-performance servers and the cooling systems employed to dissipate the heat produced by them are characterized by their exceptionally high and relatively flexible energy consumption characteristics. The high energy consumption rate of data centers has become so significant that it constituted 1.7% of global energy consumption by 2022. With such high energy consumption, the flexible load characteristic of data centers allowing energy demand to be adjusted over time makes them valuable and suitable players to participate in demand-side management (DSM). This contributes to sustainability efforts by making the energy use of data centers more effective and economical. To achieve this, it is essential to develop decision-making tools that accurately estimate data center energy demand and create optimal energy management schedules. In this chapter, an analysis of trends in data center energy consumption, power models, and their role in DSM is covered. Additionally, a case study involving the development of a decision support system comprising forecasting and optimization modules is provided. It is concluded that the proposed approach can lead to in a 16.9% decrease in the energy costs of data centers. © 2024 Elsevier Inc. All rights reserved.
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    Performance Analysis of Different Optimization Algorithms on Overcurrent Relay Coordination Problem in Distribution Systems
    (IEEE, 2022) Atsever, Mert Bekir; Karacasu, Ozgur; Hocaoglu, Mehmet Hakan
    One of the main protection methods in distribution systems is over-current protection. Although, over-current protection offers economic solution to the operators; optimal over-current coordination must be established between relays in order to provide fast and selective protection. Thus, over-current relay coordination problem can be constructed as an optimization problem with number of constraints. Meta-heuristic optimization algorithms have widely been employed to obtain better solution. Many optimization algorithms have been conducted by various researchers. Also introduce recently developed optimization algorithms that are applied on over-current relay coordination problem first time in the literature. In this study, performance analysis of different optimization algorithms is carried out by using sample test cases from the literature. Also two recently developed optimization algorithms are applied on over-current relay coordination problem.
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    Performance analysis of three-phase five-leg transformers under DC bias using a new frequency-dependent reluctance-based model
    (John Wiley and Sons Inc, 2022) Canturk, Sevket; Balci, Murat Erhan; Hocaoglu, Mehmet Hakan; Koseoglu, Ahmet Kerem
    This paper presents a reluctance-based model considering the frequency-dependent loss nature of the windings for the analysis of three-phase five-leg transformers under grid voltages with direct current (DC) bias. This is very important especially for proper determination of their harmonic current distortion and maximum loading capability (MLC) under DC-biased grid voltage conditions. To figure out the developed model’s validity under sinusoidal and DC-biased grid voltage cases, it is comparatively analyzed with the model based on 2D finite element method (FEM). Thus, for the considered transformer type operated under DC bias, the excitation current’s harmonic pollution, losses, and reactive power demand parameters are analyzed by using the developed model. Additionally, by regarding these performance parameters, the DC susceptibilities of the considered-type transformer and the single-phase shell-type transformer are comparatively evaluated. Finally, for the studied grid voltage conditions, the effects of two important design considerations as (i) magnetic core material selection and (ii) legs’ cross-sectional area sizing on the MLC are investigated. It is concluded from these investigations that under saturation conditions, the transformers, which have the core material with higher permeability or lower reluctance, draw higher excitation current, and have lower MLC ratio when compared to ones having the core material with lower permeability or higher reluctance. However, for unsaturated transformers, which work under DC bias, the case is the opposite to that in saturation conditions. On the other hand, under DC bias conditions, the effect of cross-sectional area sizing on the MLC ratio is much more for the transformer with high permeable magnetic core material with regards to ones with low permeable magnetic core material.
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    Time characteristic curve based earth fault relay selectivity assessment for optimal overcurrent relay coordination in distribution networks
    (IEEE, 2022) Atsever, Mert Bekir; Hocaoglu, Mehmet Hakan
    Coordination of overcurrent relays has been handled with optimization techniques. Time and pick up settings are optimized by using three-phase fault magnitudes. Generally, Standard Inverse Characteristic (SIC) has been used for threephase fault protection settings. However, single line to earth fault is the most common fault types in distribution networks. Definite Time Characteristic (DTC) is, widely, used for coordination of earth fault relays. Topology type, neutral earthing resistance and capacitive currents of underground cables may cause selectivity issues when DTC is used for the coordination. In this work, time characteristic curve (TCC) based earth fault relay selectivity assessment carried out on distribution network. Different earthing resistance and TCC are taken into account during optimization processes. Results show that both DTC and SIC have issues in terms of operating time and selective protection.
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    Zero-sequence based fault location in non-effectively earthed distribution systems
    (IEEE, 2022) Atsever, Mert Bekir; Deveci, Umur; Yilmaz, Seyit Cem; Hocaoglu, Mehmet Hakan
    Earth faults are detected and located by using zero sequence current magnitude in the field. However, distribution networks may have different neutral earthing strategies, generally, preferred by distribution system operators or enforced by regulatory bodies. Different earthing practices create difficulties for earth fault location problems. In addition to this difficulty, heavy underground cable usage increases the capacitive current levels of the system. Circulating capacitive currents during the single line to ground faults may further hinder the effectiveness of earth fault location algorithms. This work presents zero sequence magnitude-based fault location performance on 151-node distribution network considering different earthing methodologies and line types.