Generatörlerin Otomatik Senkronizasyonu

Abstract

Özellikle büyük çaplı sanayi kuruluşları için elektrik enerjisinin kalitesi ve sürekliliği ciddi önem arz etmektedir. Bunun sonucu olarak bu kuruluşlar ihtiyaçları olan elektrik enerjisini üretecek ekipmanlar ile donatılmıştır. Bunların bir kısmı sadece acil durumlarda tesisteki önemli yükleri besleyebilecek kapasitede olabileceği gibi tüm sistemin ihtiyacı olan elektrik enerjisini sağlayabilecek kapasitede olanları da mevcuttur. Hatta birçok tesis ihtiyaç duyduğu enerjinin fazlasını üreterek diğer sanayi kuruluşlarına satmaktadır. Bu durum enerji verimliliği ve sürdürülebilirliğini sağlamasının yanısıra, birer elektrik tüketicisi olan bu tesislerin üretici konumuna geçerek, ekonomik olarak fayda elde etmesine de imkan tanımaktadır. Elektrik tesislerinde üretim genel olarak birden fazla generatörün paralel olarak bağlanması ile elde edilmektedir. Bu durum sistemin arızalara olan toleransını arttırıp, bakım maliyetini azalttığı gibi, sistemin daha verimli çalışmasını ve daha yüksek güç elde edilmesini sağlamaktadır. AC kaynaklar sadece ve sadece birbirleri ile senkron olma durumunda paralel olarak bağlanabilmektedir. Aksi halde başta generatör olmakla birlikte tüm elektriksel ekipmanın hasar görmesi kaçınılmazdır. Kaynakların birbiri ile senkron olup olmadığını ölçmek için çeşitli yöntemler mevcuttur. Bunlardan en basit olanı senkronizasyon lambalarıdır. Diğer bir yöntem ise kaynaklar arasındaki gerilim, frekans ve faz farkını gösteren çift voltmetre, çift frekansmetre ve senkronoskoptur. Teknolojinin ilerlemesi ile sistemin senkron olup olmadığının kontrolü sayısal koruma rölelerine “synchronism check” ismi ile entegre edilmiştir. Kaynakların paralel operasyona alınma işlemi sırasında bir operatör tarafından generatöre kumanda işaretleri gönderilmektedir. Ancak günümüzde hataları azalmak ve daha yumuşak bir senkronizasyon gerçekleştirmek amacıyla geliştirilen otomatik senkronizasyon cihazları ve sayısal koruma röleleri ile gerekli kontrol işaretleri üretilebilmektedir. Az sayıda generatörün olduğu ve senkronlamanın sadece kaynakların şebekeye bağlandığı noktalarda yapıldığı uygulamalarda, her generatör için birer otomatik senkronizasyon cihazı kullanılarak çözüm üretilebilmektedir. Fakat senkronlamanın çok sayıda noktadan yapıldığı, çok sayıda generatörün bulunduğu karmaşık yapıya sahip tesislerde bu çözüm yeterli olmamaktadır. Bu nedenle karmaşık sistemlerde otomatik paralelleme cihazının yanı sıra sistemin senkronlama işlemine uygun olup olmadığını denetleyen ve otomatik senkronlama cihazını yönlendiren bir kontrolör tasarlanmalıdır. Bu tez çalışmasında örnek bir tesis için otomatik senkronlama sistemi tasarlanıp, gerçeklemesi yapılmıştır. Bir otomatik paralelleme rölesi ve bir senkronizasyon kontrolöründen oluşan sistem, birden fazla generatörün birbirleri ile ve harici enerji kaynakları ile senkronizasyonunu otomatik olarak gerçekleştirmektedir. Kontrolör anlık olarak elektrik şebekesinin durumunu gözlemleyerek sistemin otomatik senkronlamaya uygun olup olmadığına karar vermektedir. Eğer sistem otomatik senkronlamaya uygunsa, yine şebekenin o anki durumuna göre kontrol edilmesi gereken generatör veya generatörleri saptayarak, otomatik paralelleme cihazının bu generatörleri kontrol etmesini sağlamaktadır.

Quality and sustainability of electrical energy became more an issue for industrial corporations espacially those have large-volume production plants. Thus, these plants have been equipped by systems, which are capable of generating electrical energy, that plant needs. Some of these system’s capacity can barely supply for only high priority loads in facility and some of them supply the electrical energy of entire system. Furthermore, many of these facilities producing more than the energy that they needed to sell oversupplied energy to other industrial corporations. As a consequence, achievement of energy efficiency as well as sustainability, enables these companies to obtain economical benefits through becoming producers of electrical energy from a position of energy consumers. In general, energy production is achieved by more than one generator that connected in parallel. When a generator fails or stops due to the maintenance, power loss will be relatively small so this connection increases system’s fault tolerance and decreases maintenance costs of system, and enables system work more efficiently and gain more power. AC sources can only be connected in parallel if only the difference between their voltage, frequency and phase angle must be in the range that standardized by IEEE. Also phase sequence and the waveform of these two system must be same. Systems that fulfill these requirements are called synchronous. The operation, getting systems in synchronous is also called synchronization. AC systems have to be synchronized before parallelling. Otherwise it is inevitable that all of electrical equipments located in the plant, notably the generator gets damaged. Another problem of connecting systems without synchronization is loss of energy quailty and sustainabilty due to the reactive power generation or consumption and trips of protection relays. There are many methods to determine whether systems are working synchronous or not. Synchronization lamps method, consists of AC lamps connected between phases of the two system is the simplest way of among. Another method includes double voltmeter, double frequency meter and synchronoscope those indicates voltage, frequency and phase difference between sources. With the advancement of technology, the name of checking whether the system is synchronous or not, “synchronism check” function, gives closing permission to the circuit breaker that electrically connects two systems only in synchronous conditions is integrated into digital protection relays. Synchronization process can be handled manually or automatic. In manual synchronization, balancing commands that controls the generator’s speed and excitation current to adjust voltage and frequency are produced by an operator till the two systems have admissible voltage and frequency difference. Circuit breaker closing command is also sent by the operator after making sure the phase difference between the systems, measured by synchronization lamps or synchronoscope is acceptable. In automatic synchronization, balancing commands and circuit breaker closing command are produced by an automatic synchronization device. This prevents operator based faulty synchronizations and provides a smoother synchronization. Using automatic synchronizers solely for each generator, can provide a solution for such applications that have a small amount of generators and work synchronous in only sources and national network. But this solution will not be sufficient for facilities that have a complex system structure with large amount of generators and synchronized in plenty of different synchronization points. Thus, for such of complex systems, in addition of automatic paralleling device there should be also a synchronization controller, that will drive automatic paralleling device, decieding which generator to be controlled and also capable of checking if the system is available for synchronization or not needs to be designed. In this thesis work, an automatic synchronization system designed and implemented for a sample plant. The system which performs automatic synchronization between multiple synchronous generators in each other and also with external energy sources has an automatic parallelling device and a synchronization controller. The controller checks the system if it’s suitable for synchronization or not by checking instantly the electrical grid’s configuration. If the system is suitable for automatic synchronization, It determines which generator or generators will be controlled by the help of network configuration and allows automatic synchronizer to synchronize. Measurement of phase angle, voltage and frequency of the systems are done via voltage transformers located at each busbar and line side of synchronous feeder. Synchronization controller selects the relevant voltage information according to synchronization point and lead them to automatic synchronizer’s voltage inputs. The reference voltage input is busbar voltage by default. But if it is necessary, reference input is inverted with line voltage by synchronization controller. It is critical that mircro circuit breakers, located at the secondary side of the voltage transformers not tripped. If it’s so, the automatic synchronization device would judge it as no voltage and lead system into faulty synchronization. So, health of voltage transformer’s micro circuit breakers must be supervised by synchronization controller. Another critical function that synchronization controller must perform is checking the health of switchgear positions. Grid configuration is determined at runtime by synchronization controller with the help of the disconnector and circuit breaker positions. Any faulty position determination cause controlling wrong generator. To prevent this, all switchgear positions measured as double point indication, consists of two seperate switch, positioned switchgear’s both on and off position. At this method, only one switch have to be energized at a position. If there is no enegized swicth exists, it is called intermediate position and should be ignored for a limited time when switchgear is changing it’s position. If both of the switches energized, this is judged as faulty position. Permanent intermediate position and faulty position are show the switchgear position is unhealthy. If there is any feeder that has unhealthy position, exists in the plant, automatic synchronization must be blocked. This task is modelled and programmed using discerete event system simulation on controller. Health of automatic synchronization device also critical for proper synchronization. This is measured by automatic synchronizer’s live contact. Synchronization controller checks the grid’s actual state to deciede whether it is suitable for synchronization for selected synchronization point. Being off position for synchronization circuit breaker and being on position for at least one of the busbar disconnectors are necesssary for synchronization. Generators, which will be synchronized are determined with grid configuration identification method dynamically at runtime. This is calculated with actual positions of disconnectors and circuit breakers. Active sources of each feeder are calculated with combining coefficient matrixes of sources, coupling feeders and transfer feeders. After calculation of active sources of each feeder, synchronization scenarios created using the source status of both side of synchronization circuit breaker. If any side of circuit breaker has no voltage, synchronism-check function will be sufficient. If any side of circuit breaker suppied with generators and the other one supplied with utility power, synchronization with balancing commands should be done. Synchronization has to be blocked when both sides of circuit breaker supplied with different utility power sources. When the both sidec of circuit breaker supplied with different generators, decision of which generator will be synchronized to each other is made with the concept of leader generator which works under power. In other words, a generator that capable of getting more load, is synchronized to other. This information can be measured by synchronization system or taken from another systems like load shedding. Leader generator information is also used when sending balancing commands to the multiple generators, working in synchronous. Balancing commands for voltage are sent to all generators but, balancing commands for frequency are only sent to the leading generator and assuring that other generators would follow it’s speed according to the theory of synchronous machines. Synchronization controller leads balancing commands which are generated by automatic synchronizer to only related generators, decieded by grid configuration identification. When two systems become synchronous, circuit breaker closing permission, also geneterated by automatic synchonization device is sent to the related feeders circuit breaker. If synchronization circuit breaker changes it’s position to on position within determined time interval, This would be intrepreted as successful synchronization. Otherwise it would be synchronization failure due to timeout. In other words, Systems wanted to be synchronized, couldn’t become synchronous for given time interval. In this situation, automatic synchronization could be restarted or systems manually synchronized without time restriction. It is recommended that, developing a SCADA system containing single line diagram of the plant, enables operator to select synchronization point and perform automatic and manual synchronization with full alarm management. But a mimic panel that has command functions and basic alarm indicators, is also enough for operator to perform synchronization.