Güç Sistemlerinde Tıkanıklık Durumlarında Bara Fiyatlarının Güvenlik Kısıtlı Optimal Güç Akışı Yöntemi İle İncelenmesi

Abstract

Elektrik endüstrisinin yeniden yapılandırılması sonucu çok oyunculu yeni bir rejimin ortaya çıkışı beraberinde elektrik şebekesinin; düzenlenmesi, işletilmesi ve planlanması gibi konularda büyük değişiklikler meydana getirmiştir. Rekabetçi piyasaya girilmesinin getirdiği faydaların yanısıra daha önce rastlanmamış problemlerle de karşılaşılmıştır. Rekabetçi elektrik piyasasındaki iletim sistemi tıkanıklığı problemi, piyasa yerleşimi kaynaklı olarak enerji talebindeki değişimler, iletim hatlarının ve generatörlerin devre dışı kalması, elektrik alışverişlerinde koordinasyonun sağlanamaması, elektrik fiyatlarındaki farklılıklar, yapılan yatırımların sistemde dengeli olarak dağılamaması vb. gibi nedenlerden hatların ve transformatörlerin aşırı yüklenmesiyle meydana gelir. Günümüzde iletim tıkanıklığı artarak önem kazanan bir problem haline gelmiştir. Literatürde iletim tıkanıklığı yönetimi pek çok yazar tarafından farklı yöntemler ile ele alınmış ve çözümünde farklı modeller önerilmiştir. Tez kapsamında, tıkanıklık probleminin yönetimi için piyasa tabanlı fiyatlar kullanan marjinal bara fiyatlandırma yöntemi kullanılmıştır. Marjinal bara fiyatlandırma, diğer fiyatlandırma yöntemlerine kıyasla piyasa yapısına en uygun olan yöntemdir ve optimal güç akış yöntemi kullanılarak çözülür. Optimal güç akışının temel amacı, sistem güvenliğini sürdürürken, güç sisteminin yük talebini karşılamak için gereken maliyetin minimize edilmesidir. Çözümü için kullanılan birçok farklı matematiksel yöntem vardır ve bu çalışmada Newton Raphson metodu kullanılmıştır. Newton metodu, sonuca hızlı yakınsamasında dolayı güç akışının çözümü için kullanılan yöntemler arasında en çok kullanılanlardandır. Kullanılan diğer bir çözüm yöntemi ise DC güç akışıdır. Bu faktörlerden ikisi olan üretim değişim faktörleri ve iletim hattı açması durumunda dağılım faktörleridir. Üretim değişim faktörleri beklenmedik durumlarda üretim güç duyarlılıklarını tanımlar. İletim hattı açması durumu dağılım faktörü (LODF), sistemde bir iletim hattı devre dışı kaldığında diğer hatlar üzerindeki güç akışı değişimini gösterir. Tez çalışmasında, Powerworld Simulator programı kullanılarak IEEE 14 baralı örnek test sistemi üzerinde meydana gelebilecek olağandışı durumlar güvenlik kısıtlı optimal güç akışı yöntemi ile incelenmiş ve bu durumlarda oluşan marjinal bara fiyatlarındaki değişimler gözlemlenmiştir. Sistemdeki maksimum zorlanmalara neden olabilecek durumlar yine Powerworld programı ile olağandışı durum analizi yapılarak belirlenmiştir. Elde edilen analiz sonuşları yorumlanmıştır.

The restructuring of the electricity industry has created a new regime with many new market players. Plenty of changes brought huge shifts in the planning, operations and management of power systems. The introduction of competitive markets did not only bring advantages, but also made the electric power industry face unprecedented problems. In the competitive markets, the transmission congestion may be caused due to various reasons, such as transmission line outages and generator outages, change in energy demand. In the present day scenario, the tranmission congestion management gained much attention around the world. Transmission congestion management was analyzed with different methods and different models were formed for solution by a lot of authors in literature. In this thesis, Locational marginal pricing (LMP) is a mechanism for using market based prices for managing transmission congestion. Locational marginal pricing is the best appropriate method in comparison with other pricing methods. LMP consist of three main component as energy, loss and congestion. The energy component of LMP represent the marginal cost of energy at reference (slack) bus. It is determined using margial energy offer of generator. The congestion component and loss component of LMP are equal to zero at reference bus so locational marginal price is equal to the energy component. Furthermore, when there are no transmision congestion and loss at the power system, marginal cost of each bus at the system is equal to marginal cost of referans bus. LMP is solved using optimal power flow method. The objective of the security constraint optimal power flow is to minimize the costs of meeting the load demand for a power system while maintaining the security of the system. Maintaining system security requires keeping all equipment in the power system within its desired operating range at steady-state. This will include keeping system bus voltages within specified ranges, maximum power flows on transmission lines and transformers and maximum and minimum outputs for generators. Another objective of optimal power flow is to specify marginal cost data of electric power system. This marginal cost data provide to pricing of active power transaction as well as pricing of auxillary servis as voltage support. OPF can perform all control function that required for power system. Economic power dispatch, while controlling the active power output of the generator, the OPF can also control transformer taps and transformers phase shifts. Many different mathematical techniques exist in the literature to solve SCOPF. In this thesis Newton Raphson method is choosen for solution of SCOPF because it is a very powerful solution algortihm because of its rapid convergence near the solution. Second part of this thesis, IEEE 14 bus test system is simulated using Powerworld Simulator program. First of all, contingency analysis is performed to calculate violation in IEEE 14 bus test system with Powerworld. The contingency analysis is classified as single contingency and multiple contingency. As a result of this analysis, total 110 contingency are detected in the test system. The five worst-cases has been choosed in contingency analysis result of the test system. In addition, the total load demand is increased from 259 to 362,2 MW in the IEEE 14 bus test system so there is a transmission congestion in the transmission line to serve the load. Line contingency and generator contingency are generally most common type of contingencies. These contingencies mainly cause two types of violations as low voltage violations and line power limits violations. The operating range of voltage at any bus is 0.9-1.1 p.u. in IEEE 14 bus test system. Thus, if the voltage falls below 0.9 p.u then the bus is said to have low voltage. If the voltage rises above the 1.1 p.u then the bus is said to have a high voltage problem. Line power limit violations occurs in the system when the power rating of the line exceeds given rating. This is mainly due to the increase in the current flowing in that line. Furthermore, another solution method in Powerworld simulator is DC load flow. These factors can be derived in a variety of ways and are explained in this study. Generation shift factors (GSDF) describing a generator power sensitivity under the contingency condition and line outage distribution factors (LODF) describing change in the flow on one line caused by the outage of a second line are two types of these factors and they are used to analyse single contingency which caused by the outages of a generator or a transmission line in this thesis. Remedial Action Schemes (RAS) are the key components for any power system planning. These are the steps which need to take in order to get the system back to its normal operation. Remedial Action Scheme (RAS) are the necessary actions which need to be taken to solve the violations caused by a contingency. Shunt capacitor switching, generation re-dispatch, load shedding and load tap changing (LTC) transformer are types of RAS that used in this study. Load shedding is undesireble type of RAS in a power system. However, when transmission congestion could not be solved by other methods mentioned above, load shedding is performed as the latest solution in the test system. Five worst-cases that selected in contingency analysis results and another case that increased load demand in the system are solved using security constrain optimal power flow (SCOPF). After that locational marginal prices was observed in this determined cases and a significant increase has been seen in the locational marinal prices of buses at system because of transmission congestion. At the same time, transmission line outages and generator outages caused low voltage violations in the IEEE 14 bus test system. This problem is solved with control of reactive power using control of transformer tap and Shunt capacitor switching. In addition, it help control of active power and reduce transmission congestion. Active and reactive power changes in the test system and their effects on transmission congestion are observed for each cases that analyzed using SCOPF in the test system. Having information about various violation in the power system effects on locational marginal price is very important for system operator. Thanks to this data, system operator can make a right decision to alleviate transmission congeston.