Dağıtık üretimli şebekelerde adalaşma tespiti = Islanding detection in distributed generation

Abstract

Yakıt hücreleri, rüzgar türbinleri, fotovoltaik enerji gibi yeni teknolojilerdeki ilerlemeler ile birlikte güç elektroniğindeki yenilikler, müşterilerin daha iyi güç kalitesi ve güvenilirlik için talepleri, enerji endüstrisini dağıtık tesisler için değişmeye zorlamaktadır. Dolayısıyla dağıtık üretim (DÜ) son zamanlarda piyasa deregülasyonları ve çevresel kaygılar nedeniyle enerji endüstrisinde büyük bir ivme kazanmıştır. Dağıtık üretim kaynaklarının şebekeye entegrasyonu bazı teknik zorluklar oluşturmaktadır. Adalaşma bu teknik zorluklardan biridir. Adalaşma, dağıtım sisteminin bir kısmının güç sisteminin geri kalanından elektriksel olarak ayrıldığı durumda oluşmak ile birlikte aynı zamanda dağıtık jeneratörler tarafından sistemin geri kalan kısmına enerji verilmeye devam etmesi ile meydana gelir. Bir dağıtık jeneratörü güç dağıtılmış sisteme bağlamak için önemli bir gereklilik, dağıtık üretim sisteminin ada tespitini algılama yeteneğidir. Ada durumunda jeneratörlerin devreye girmemesi, jeneratörler ve bağlı yükler için bir takım sorunlara yol açabilir. Mevcut endüstri uygulaması, adalaşma durumunun ortaya çıkmasından hemen sonra tüm dağıtık jeneratörlerin bağlantısını kesmektir. Genel olarak, dağıtılmış bir jeneratörün bağlantısı, ana beslemenin kesilmesinden sonra 100 ila 300 ms içinde kesilmelidir. Böyle bir hedefe ulaşmak için, her dağıtık üretim kaynağının, vektör dalgalanma rölesi ve frekans değişim oranı rölesi gibi ada oluşturma önleyici cihazlar olarak da adlandırılan bir ada tespit cihazı ile kullanılmalıdır. Bu rölelerin dışında adalaşmayı tespit etmek için bazı yöntem ve teknikler bulunmaktadır. Bu yöntemler bölgesel ve endirekt teknikler olarak iki başlık altında toplanmaktadır. Bu çalışmada, ETAP programının ANSI standartına göre hazırlanmış örnek devresi üzerinden analiz çıktıları elde edilmiştir. 2.5 MW gücünde ki rüzgar türbininin entegre edildiği durumda oluşan bir sistem vaka çalışması ele alınmış ve ada durumunda rüzgar türbininin bağlı olduğu baranın frekans ve gerilim değerlerine bakılarak ada durumunun tespiti konusunda sonuçlara varılmıştır. Ada durumunda rüzgar türbininin hatve açısı, aktif güç, reaktif güç ve mekanik güç değerlerinde değişim kullanılarak ada tespiti konusunda çalışmalar yapılmıştır. Yapılan incelemeler; normal çalışma, ani yük değişimi, rüzgar türbininin şebekeden kopma durumu gibi ada oluşturma ve olası ada dışı koşullar üzerinde test edilmiştir. Güç dağıtım şebekesinde ada durumunda oluşan durum tespitinde frekans, gerilim ve rüzgar türbininin hatve açısı, mekanik güç, aktif güç ve reaktif güç üzerindeki etkileri üzerinden elde edilen veriler ile sonuca ulaşılmıştır.

The integration of renewable energy sources into the electricity transmission and distribution system is increasing. As a result of identifying the problems that will occur in this system integration at the design stage and proceeding with the appropriate engineering approach; the need for backup of renewable energy with conventional generation systems will be reduced and the complex structure that may occur as a result of integration will be overcome. This thesis is an investigation of the problems between a distributed generation facility and the non-DG part of the grid to which it is connected. The problem can be defined as islanding in power systems. Advances in new technologies such as fuel cells, wind turbines, photovoltaic energy, innovations in power electronics, customer demands for better power quality and reliability are forcing the power industry to change for distributed generation. Therefore, distributed generation (DG) has recently gained great momentum in the power industry due to market deregulations and environmental concerns. . In today's world where energy sustainability is becoming more important for societies, renewable energy sources have become very important and the number of distributed generation plants is increasing day by day. An important reason for the spread of distributed generation power plants is to eliminate the problem and cost of transporting large power plants as a result of transmission lines where the distance between the end consumer is quite high. With the widespread use of distributed generation power plants, the problems experienced in transmission lines and the construction cost of new lines are significantly reduced. Thanks to distributed generation power plants, the power to be sent to the electricity grid during the planning process is reduced and the need for energy transmission lines is eliminated. DG can be designed in line with the load demand of the end consumer. Since it is not high-powered, it provides convenience in terms of plant construction time and the region where the plant will be built. Thanks to its modular design, it can be installed in the desired area. Since it has the flexibility to operate independently from each other, the capacity can be increased in case of an increase in load demand. The addition of DG to the existing electrical power distribution system may lead to a decrease in the protection reliability, system stability and quality of the power supplied to customers. The integration of distributed generation resources into the grid poses some technical challenges. One of the most important of these is islanding. Islanding is a situation that occurs when the DG system is disconnected from the main distribution network to which it is connected and continues to supply a distribution region. As a result of incorrect operations by the system operators or possible short circuit or malfunction in the distribution network, islanding may occur in a certain region. Islanding occurs when a part of the distribution system is electrically separated from the rest of the power system, while at the same time the rest of the system continues to be energised by distributed generators. An important requirement for connecting a distributed generator to a power distributed system is the ability of the DG to detect islanding. Failure of generators to switch on in an islanding situation can lead to a number of problems for generators and connected loads. Islanding is generally considered undesirable due to potential damage to existing equipment, grid problems, reduced power reliability and power quality. Current industry practice is to disconnect all distributed generators immediately after the occurrence of an islanding condition. In general, a distributed generator should be disconnected within 100 to 300 ms after disconnection of the main supply. In order to achieve such a goal, each distributed generation source should be equipped with an islanding detection device, also called islanding prevention devices, such as vector surge relay and ROCOF relay. Apart from these relays, there are some methods and techniques to detect islandisation. These methods are categorised under two headings as local and indirect techniques. The basic philosophy of fairness detection is to monitor the output parameters of the DG and the system parameters and/or to determine whether the fairness situation occurs from the changes in these parameters. Although localised techniques are more reliable than indirect techniques, this method is not economical in terms of application. The regional techniques and methods used for islanding are mainly based on the measurement of system parameters such as voltage, frequency, etc. at the DC site. It is also analysed under two main headings as passive detection techniques and methods and active detection techniques and methods. Passive techniques use the information available on the DG side to determine whether the DG system is isolated from the grid. Passive methods are based on the principle of measuring system parameters such as voltage, frequency, harmonic distortion, etc. These parameters change drastically in the case of islanding. The difference between the islanding state and the grid connected state is due to the difference between the threshold values of the parameters and the current state. In the islanding state, special care must be taken when setting the threshold value to distinguish it from other interference in the system. The advantage of passive techniques is that the application has no influence on the normal operation of the DG system. Active techniques initiate an external perturbation at the output of the inverter. They tend to respond faster and have a smaller undetected region compared to passive approaches. The system modelled in this study is an example system model prepared according to the ANSI standard in ETAP software. The wind turbine has a type 3 doubly fed inductive generator and the operating mode is selected as voltage control in the ETAP programme. In the study, a 2.5 MW wind turbine integrated system is considered and the frequency and voltage values of the busbar to which the wind turbine is connected in case of islanding are analysed and conclusions are drawn about the detection of the islanding situation. In case of islanding, studies on islanding detection were carried out by using the changes in the pitch angle, active power, reactive power and mechanical power values of the wind turbine. The analyses were tested on islanding and possible off-island situations such as normal operation, sudden load change, disconnection of the wind turbine from the grid, and the results were reached with the data obtained through the effects of the wind turbine on frequency, voltage and pitch angle, mechanical power, active power and reactive power in the detection of islanding in the power distribution network. As a result of the analysis outputs, it is seen that voltage or frequency parameters alone will not be sufficient for islanding detection. Voltage is a parameter used for islanding detection. The operation of the wind turbine in type 3 voltage control mode prevented the voltage drop in case of islanding. The fact that the wind turbine is selected as type 3 2.5 MW has been seen to have an improving effect on the system to which it is connected. With this study, the responses of wind turbines in the islanding situation have been clearly seen. The responses of the wind turbine in the islanding situation enable the determination of improvement opportunities for wind turbine manufacturers.