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Accuracy assessment of frequency-domain models for harmonic analysis of residential type photovoltaic-distributed generation units
(Elsevier, 2022) Karadeniz, Alp; Öztürk, Onur; Köksoy, Ahmet; Atsever, Mert Bekir; Balcı, Murat E.; Hocaoğlu, Mehmet Hakan
Since Photovoltaic-Based Distributed Generation Units (PV-DGUs) have power electronic interfaces for their grid integration, they can cause harmonic pollution in the system. Thus, the harmonic analysis is required to determine the system’s harmonic constrained PV-DGU hosting capacity and proper planning of the harmonic mitigation devices and PV-DGUs. The accuracy of the harmonic analysis highly depends on the validity of the system equipment models. Accessible literature shows that there is not a report on accuracy assessment of the PV-DGU frequency-domain harmonic models. In this paper, firstly, for numerous distorted grid voltage conditions, the current harmonic distortion nature of the single-phase transformerless two-level H-bridge residential type on-grid PV inverter is examined in an experimental test system. Secondly, for current harmonic analysis of the examined PV inverter, the accuracy of the widely known frequency-domain models is statistically analyzed under numerous distorted grid voltages. For the accuracy assessment of the models, the measurements obtained from an experimental test system are considered as reference values. Finally, to investigate the effect of the models on the voltage harmonic distortion results of the harmonic analysis, the harmonic penetration analysis algorithm is integrated with the models, and it is simulated for IEEE 33 bus test system.
Aşırı akım röle koordinasyonu için bozkurt algoritmasının kapsamlı performans analizi
(Tmaed, 2022) Atsever, Mert Bekir; Hocaoğlu, Mehmet Hakan
Güç sistemlerinde aşırı akım koruma pratiği, mesafe koruma pratiğinden daha ekonomik ve yaygındır. Ayrıca dağıtım şebekelerinin büyük bir çoğunluğunda aşırı akım koruma kullanılmaktadır. Bu durum, dağıtım şebekelerinde kullanılan aşırı akım rölelerin koordinasyonun en uygun şekilde tasarlanmasını gerekli kılmaktadır. Aksi halde sistemde gerçekleşen bir arıza sırasında röleler istenildiği gibi çalışamaz. Aşırı akım röleleri arasında koordinasyonun etkili ve seçici olabilmesi için röle ayar parametrelerinin şebekeye uygun ayarlanması gerekmektedir. Dağıtım şebekelerinin genişlemesi ile birlikte röle ayarlarının hesaplanması veya güncellenmesi zorlaşmıştır. Bu nedenle aşırı akım röle koordinasyonu yüksek sayıda kısıt içeren optimizasyon problemi şeklinde kurgulanmaktadır. Optimizasyon problemini çözümü noktasında ise peç çok meta-sezgisel algoritmalar geliştirilmiştir. Bu çalışmada IEEE 8 Baralı test şebekesi için Bozkurt Optimizasyon Algoritması (BOA) başarılı bir şekilde uygulanmış ve kapsamlı performans analizi gerçekleştirilmiştir.
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.
Evirici Devreli Dağıtık Üretim Tesislerinin Güç Sistemlerine Azami Katılımı Için Optimal Pasif Harmonik Filtre Boyutlandırma Ve Yerleştirme Algoritması Geliştirmek
(2019) Balcı, Murat Erhan; Kuvat, Gültekin; Hocaoğlu, Mehmet Hakan; Atsever, Mert Bekir; Karadeniz, Alp
Bu araştırma projesinde ilk olarak, programlanabilir gerilim kaynağı, yük ve evirici devreli dağıtık üretim birimi (fotovoltaik dağıtık üretim birimi: FDÜB) barındıran bir test sistemi kurulmuştur. Bu sistemde elde edilen ölçüm verileri ile test sisteminde yer alan FDÜB için harmonik akım kaynağı (HAK), Norton eşdeğer devre (NED) ve çapraz frekans admittans matris (ÇFAM) modelleri oluşturulmuştur. Bu modellerin harmonik akımlarının hesabında yaptıkları hataların analizi, aynı test sisteminde elde edilen çok sayıda ölçüm sonucu referans alınarak istatistiksel şekilde değerlendirilmiştir. Yapılan analiz neticesinde, modellerin hassasiyet bakımından en iyiden en kötüye NED, ÇFAM ve HAK şeklinde sıralandığı görülmüştür. İkinci olarak, HAK ve NED modelleri, harmonik etkileşim analizi (HEA) ve tam harmonik güç akışı (THGA) algoritmalarına entegre edilerek, IEEE 33 bara test sistemi için HEA-HAK, HEA-NED, THGA-HAK ve THGA-NED algoritma-model çiftlerinin MATLAB kodları hazırlanmıştır. FDÜB?lerin yanı sıra doğrusal ve doğrusal olmayan yüklerin de bulunduğu aynı sistem için yapılan çalışmalar neticesinde, bu dört farklı algoritma-model çifti arasında, elde edilen bara gerilimi toplam harmonik bozulma (THDV) profilleri bakımından önemli farklar olduğu çıktısına ulaşılmıştır. Son olarak, baralara ait maksimum THDV değerinin minimizasyonu, bara gerilimlerinin rms sapma değerinin minimizasyonu ve sistemin FDÜB barındırma kapasitesinin maksimizasyonunu amaçlayan optimal FDÜB ve pasif filtre (PF) planlama yaklaşımı önerilmiştir. Önerilen yaklaşımda kısıt olarak; geleneksel FDÜB planlama kısıtları ile IEEE 519 standardında tanımlı gerilim harmonik sınırlamaları dikkate alınmıştır. Bununla birlikte, optimal PF planlama çalışmalarının gelenekselleşmiş bir amacı olan THDV minimizasyonu, optimal FDÜB ve PF planlama probleminin çözümünde amaç fonksiyonu olarak dikkate alınmıştır. Böylece, aynı kısıtlar için geleneksel ve önerilen yaklaşımların sonuçları IEEE 33 baralı test sisteminde karşılaştırmalı olarak analiz edilmiştir. Analizler sırasında, harmonik analiz yöntemi olarak yukarıda belirtilen algoritma-model çiftleri dikkate alınmış ve çözüm yöntemi olarak literatürde çok yeni olan Balina optimizasyon algoritması kullanılmıştır.
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.
Method-hybridization for preventing capacitive current based false trips in Turkish cable dense distribution networks
(Gazi Universitesi, 2024) Atsever, Mert Bekir; Hocaoğlu, Mehmet Hakan
Modern distribution networks have constantly evolved to meet different requirements. Basically, increasing energy demand and supply security are the main motivation for these changes. In order to meet the increasing energy need, there are many parallel outgoing feeders in the distribution substations, and there is an intense use of underground cables to increase supply security. During single line to earth fault, zero sequence currents circulate in the system due to cable capacitive currents of underground cables. These capacitive charging currents may cause false trips in healthy sections of the network. Metropolitan distribution networks draw particular attention with distinguishing topological features which are; the usage of long-length underground cables and high number of parallel outgoing feeders. In addition, different types of earthing methods are applied. This situation eliminates the applicability of simple, unique and universal relay settings for all types of networks. As a result, the requirement of feeder-based protection hybridization, specifically tailored to the distribution network topology is inevitable. In this study, feeder-based hybrid protection methods and optimum setting values of these methods are proposed for different network topologies and different neutral earthing methods. The method-hybridization is applied to the 62-busbar distribution network to demonstrate the applicability of the proposed method.
Mitigation of sympathy trips in highly cabled non-effectively earthed radial distribution systems via MINLP
(Elsevier Ltd, 2023) Atsever, Mert Bekir; Hocaoğlu, Mehmet Hakan
Sympathy tripping problem simply refers to unnecessary operation of healthy feeder protection relays. Capacitive currents of underground cables are the main cause of sympathy tripping during the single line-to-earth faults (SLEFs) in non-effectively earthed distribution systems. Sympathy trips cause unnecessary loss of loads, increase the amount of energy-not-sold and deteriorate reliability indices. To prevent sympathy tripping in the presence of the circulating capacitive currents during the SLEF, pick-up current settings of earth fault relays should be optimized in accordance with the network topology. Accordingly, in this paper, a novel objective function and constraints have been formulated and solved using Mixed-Integer Non-linear Programming (MINLP) for optimizing the earth fault relay settings. The effectiveness of the proposed methodology has been tested by considering the effects of different cable cross-sections, fault locations, and fault resistances on a real distribution network. Therefore, with the developed MINLP approach, sympathy tripping problem is prevented. Selective protection can be provided by the optimized setting of earth fault relays in highly cabled non-effectively earthed radial distribution networks. More importantly, by using the proposed method it is possible to eliminate sympathy tripping in different radial typologies such as different numbers of parallel feeders, voltage levels, and neutral earthing structures.
Onsite Partial Discharge Detection and Location System for Underground Cables Using USRP-Based Measurement System
(Institute of Electrical and Electronics Engineers Inc., 2024) Atsever, Mert Bekir; Boyacı, Ali; Yarkan, Serhan; Hocaoğlu, Mehmet Hakan
he accuracy of PD location is particularly crucial for mission-critical cable feeders. Highly accurate PD position estimation increases efficiency by reducing repair costs and time spent on operation. Commercial PD measurement devices generally have high costs and maintenance fees. This study proposes an easily connected, portable USRP-based PD measurement system. The effectiveness of the proposed measurement system is demonstrated by simultaneous on-site measurements with a commercial PD measurement device. The PD position obtained by the proposed method is compatible with the results obtained with the commercial PD measurement device.
Optimal overcurrent relay Coordination in distribution networks
(IEEE, 2021) Atsever, Mert Bekir; Karacasu, Özgür; Hocaoğlu, Mehmet Hakan
Over-current relay coordination plays a critical role for effective protection of networks since primary protection is based on over-current detection in distribution systems. Thus, optimal relay coordination must be ensured between relays in faulted condition, providing selectivity and fast operation. Therefore, relay coordination can be designed as an optimization problem with highly constrained equations in such networks. Linear programming, which is simple to be implemented and requires less computation time when compared other optimisation techniques, is widely employed for solving relay coordination problems. To achieve faster and selective protection a number of optimisation algorithms have, also, been customised for the purpose. Water Cycle Algorithm (WCA) is among them and has promising results, already, depicted in the literature. However, capacitive currents may jeopardize traditional optimisation process for earth faults. Thus, in this paper, performance analysis is carried out for earth faults in sample distribution networks constructed with overhead lines and underground cables, separately. The results show that in cabled networks, additional constraints are needed for the optimisation process to provide selectivity. Consequently, optimal relay settings and selective protection are ensured by adding proper constraints into optimisation problem in this paper.
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.
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.
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.

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