04-05-2011, 02:25 PM
Abstract
Static VAR compensator (SVC) is incorporated inNewton Raphson method in which Power Flow Solution is a solution ofthe network under steady state conditions subjected to certainconstraints under which the system operates. The power flow solutiongives the nodal voltages and phase angles given a set of power injectionsat buses and specified voltages at a few, both the models of SVC i.e.SVC Susceptance and Firing Angle Models are discussed. It is alsoshown that the power system losses are decreased after incorporatingthe SVC in this N-R method. The results are generated for 24-Bussystem. The reactors are thyristor-controlled and the capacitors can beeither fixed or controlled. Advanced load flow models for the SVC arepresented in this paper. The models are incorporated into existing loadflow (LF) Newton Raphson algorithm. The new models depart from thegenerator representation of the SVC and are based instead on thevariable susceptance concept. The SVC state variables are combinedwith the nodal voltage magnitudes and angles of the network in a singleframe of reference for a unified, iterative solution through Newtonmethods. The algorithm for Load Flow exhibit very strong convergencecharacteristics, regardless of the network size and the number ofcontrollable devices. Results are presented which demonstrate theprocess of the new SVC models.
I. INTRODUCTION
In electric power systems, nodal voltages are significantlyaffected by load variations and by network topologychanges. Voltages can drop considerably and even collapsewhen the network is operating under heavy loading. Thismay trigger the operation of under voltage relays and othervoltage sensitive controls, leading to extensive disconnectionof loads and thus adversely affecting consumers andcompany revenue. On the other hand, when the load level inthe system is low, over voltages can arise due to Ferrantieffect. Capacitive over compensation and over excitation ofsynchronous machines can also occur. Over voltages causeequipment failures due to insulation breakdown and producemagnetic saturation in transformers, resulting in harmonicgeneration. Hence, voltage magnitude throughout thenetwork cannot deviate significantly from its nominal if anefficient and reliable operation of the power system is to beachieved.Voltage regulation is achieved by controlling theproduction, absorption and flow of reactive powerthroughout the network. Reactive power flows areminimized so as to reduce system losses. Sources and sinksof reactive power, such as shunt capacitors, shunt reactors,rotating synchronous condensers and SVC’s are used for thispurpose. Shunt capacitors and shunt reactors are eitherpermanently connected to the network, or switched on andoff according to operative conditions. They only providepassive compensation since their production or absorption ofreactive power depends on their ratings and local bus voltagelevel. Conversely, the reactive power supplied or absorbedby rotating synchronous condensers and SVC’s areautomatically adjusted, attempting to maintain fixed voltagemagnitude at the connection points. By using FACTStechnology power system can be operated effectively andflexibly. Among the FACTS devices, the static VARcompensator is a versatile device that controls the reactivepower injection at a bus using power electronic switchingcomponents. The reactive source is usually a combination ofreactors and capacitors. This paper is mainly focuses on thedevelopment of new SVC models and their implementationin Newton-Raphson load flow algorithm. SVC statevariables are combined with the nodal voltage magnitudes[1] and angles of the network in a single frame of referencefor unified, iterative solutions using the Newton Raphsonmethod. Two models are presented in this category namely,the variable shunt Susceptance model and firing anglemodel.
II. SVC SUSCEPTANCE MODEL
The SVC is taken to be a continuous, variablesusceptance, which is adjusted in order to achieve aspecified voltage magnitude while satisfying constraintconditions. SVC total susceptance model represents achanging susceptance. svc B represents the fundamentalfrequency equivalent susceptance of all shunt modulesmaking up the SVC. This model is an improved version ofSVC models [2].SVC’s normally include a combination of mechanicallycontrolled and thyristor controlled shunt capacitors andreactors. The most popular configuration for continuouslycontrolled SVC’s is the combination of either fix capacitorand thyristor controlled reactor [3]. As far as steady stateanalysis is concerned, both configurations can modeledalong similar lines, The SVC structure shown in Fig (1) isused to derive a SVC model that considers the Thyristor-Controlled Reactor (TCR) firing angle as state variable.This is a new and more advanced SVC
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