DIMINISHING OF LOSSES IN A TRANSMISSION LINE BY USING UPFC.pdf

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International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982 Volume- 2, Issue- 3, March-2014

Diminishing of Losses In A Transmission Line By Using UPFC

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DIMINISHING OF LOSSES IN A TRANSMISSION LINE BY USING

UPFC

MALATHI.KALYANI

Department of Electrical & Electronics Engineering, Lecturer in GPT Narayan Khed, Medak, Andhra Pradesh, India.Email: [email protected]

AbstractThe Unified Power Flow Controller (UPFC) is the most versatile and complex power electronic equipment thathas emerged for the control and optimization of power flow in electrical power transmission system. This paper presents realand reactive power flow control through a transmission line by placing UPFC at the sending end. When no UPFC isinstalled, real and reactive power losses in the transmission line can not be controlled. This paper presents control and

performance of UPFC intended for installation on that transmission line to minimize losses. Installing the UPFC makes itpossible to control an amount of active power flowing through the line. Based on the conventional power system state

estimation model, a kind of model for state estimation with UPFC is introduced in this paper, in which power injectionmodel is used and the affect of UPFC on the power flow is transferred to the two nodes of the corresponding transmissionline. This method can be integrated to the conventional state estimation using MATLAB Programming with the

consideration of UPFC. To show the validity of the proposed techniques a five-bus, and an IEEE-14 bus test power systemsare proposed.

Keywords Flexible ACTransmission Systems (FACTS), Newton Rapshon Method, Losses Minimization, Real and

reactive power, Unified Power Flow Controller (UPFC).

I.

INTRODUCTION

Todays power systems are highly complex andrequire careful design of new devices taking into

consideration the already existing equipment,especially for transmission systems in newderegulated electricity markets. This is not an easytask considering that power engineers are severely

limited by economic and environmental issues. Thus,this requires a review of traditional methods and the

creation of new concepts that emphasize a moreefficient use of already existing power systemresources with out reduction in system stability and

security. In the late 1980s, the Electric PowerResearch Institute (EPRI) introduced a new approachto solve the problem of designing and operating

power systems; the proposed concept is known asFlexible AC Transmission Systems (FACTS).Thetwo main objectives of FACTS are to increase the

transmission capacity and control power flow overdesignated transmission routes. The improvements in

the field of power electronics have had major impacton the development of the concept itself. Since theconcept of flexible AC transmission systems(FACTS) was proposed by Hingorani in the 1860s,

many various FACTS devices have been utilized tomeet a growing demand of the transfer capabilitiesdue to developing wheeling transactions in the

deregulation environment. Some interestingapplications of FACTS devices can be found toeconomic dispatch(ED), AC/DC optimal power flow

(OPF), available transfer capability (ATC), contractpath based electricity trading, and transmissioncongestion management. UPFC, a versatile FACTS

device, has the unique capability to controlsimultaneously both the voltage magnitude and active

and reactive power flows on a transmission line. So,

there has been increasing interest in the analysis ofUPFC in power system. The UPFC can providesimultaneous control of all basic power systemparameters (transmission voltage, impedance andphase angle). The controller can fulfill functions of

reactive shunt compensation, series compensation andphase shifting meeting multiple control objectives.

From a functional perspective, the objectives are metby applying a boosting transformer injected voltageand a exciting transformer reactive current. Theinjected voltage is inserted by a series transformer.A new method is introduced to incorporate UPFC

devices into the power losses minimization. Thispaper attempts to deduce the model of power losseswith UPFC using the conventional power load flowstudies by using Newton-Rapshon method. A powerinjection model that transfers the affect of UPFC

towards the power flow to the two nodes is presented.This method can be integrated to the conventionalload flow studies program with the consideration of

UPFC. Furthermore, the results demonstrate that themodel is compared with and without UPFC usingMATLAB Programming.

11. Operating Principle of UPFCThe basic components of the UPFC are two Voltagesource inverters (VSIs) sharing a common dc storagecapacitor, and connected to the power Systemthrough coupling transformers. One VSI is connected

to in shunt to the transmission system via a shunttransformer, while the other one is connected in seriesthrough a series transformer. A basic UPFC

functional scheme is shown in fig.1.


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Fig.1 Basic functional scheme of UPFC

The series inverter is controlled to inject asymmetrical three phase voltage system (Vse), of

controllable magnitude and phase angle in series withthe line to control active and reactive power flows onthe transmission line. So, this inverter will exchange

active and reactive power with the line. The reactivepower is electronically provided by the seriesinverter, and the active power is transmitted to the dc

terminals. The shunt inverter is operated in such away as to demand this dc terminal power (positive ornegative) from the line keeping the voltage across the

storage capacitor Vdc constant. So, the net real powerabsorbed from the line by the UPFC is equal only tothe losses of the inverters and their transformers. The

remaining capacity of the shunt inverter can be used

to exchange reactive power with the line so toprovide a voltage regulation at the connection point.

The two VSIs can work independently of each otherby separating the dc side. So in that case, the shuntinverter is operating as a STATCOM that generates

or absorbs reactive power to regulate the voltagemagnitude at the connection point. Instead, the seriesinverter is operating as SSSC that generates or

absorbs reactive power to regulate the current flow,and hence the power flows on the transmission line.The UPFC has many possible operating modes. In

particular the power injection method is used toincrease the active power and reduce the losses in

power system.

111. Mathematical Model of UpfcThe basic structure and operation of the UPFC can be

represented through the model shown infig.2. Thesimple power-injection model is used here where theseries- and shunt converter voltages are replaced by

nodal power injections as shown in Fig 2. Themagnitude and phase angle of the series voltageproduced by the converter and the magnitude andphase angle of the AC voltage applied across. In thesteady state, the real power flowing through the shunt

converter equals the real power exchanged between

the series converter and the transmission system theshunt converter can be controlled independently.

Fig.2 Mathematical model of UPFC

Psi= -r bs vi vjsin (ij+) Psj = r bs vi vjsin (ij+)

Qsi= -r bs vi2cos Qsj = r bs vi vjsin (ij+)

Where,

1bs =

Xsrand are the UPFC variables representing the ratioof series transformer voltage to i

thbus voltage in p.u.

and the angle of the series voltage in radians

respectively. The term bs is the susceptance of theseries transformer combined with line susceptance XsThis relationship puts a constraint on the independent

control of the converters. Nevertheless, the reactivepower of the shunt converter can be controlledindependently for bus voltage or VAR control and the

power flow through the line can be controlled throughr and . For a scheduled delivery of power at thereceiving end, r and will be fixed. Besides the bus

power injections, it is useful to have expressions forpower flows from both sides of the UPFC injectionmodel defined. At the UPFC shunt side, the active

and reactive power flows are given asPi1 = -r bs vi vj sin (ij+) bs vi vj sin ij(1)

Qi1 = -r bs vi2 cos +Qconv1 bs vi

2+ bs vi vj cos ij

(2)

Whereas at the series side they are

Pj2 = -r bs vi vjsin (ij+) bs vi vj sin ij(3)

Qj2 = -r bs vi2 cos +Qconv1 bs vi2+ bs vi vj cos ij(4)

The UPFC injection model is thereby defined by theconstant series branch susceptance, bs, which isincluded in the system bus admittance matrix, and thebus power injections Psi, Qsi, Psj and Qsj. If there isa control objective to be achieved, the bus power

injections are modified through changes of the UPFCparameters r, and Qconv1 . The LF model discussedhere assumes that the UPFC is operated to keep (i)

real and reactive power flows at the receiving bus and(ii) sending bus voltage magnitude at their

prespecified values Here the Newton-Rapshonalgorithmis used to fing the load flow solution of a


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particular system The algorithm for solving a powerflow problem without and with UPFC is implemented

by using the MATLAB programming

Fig.3 Operation Scheme for minimization of losses

Fig.4 The 14- bus test system

II.

RESULT

The IEEE-14 bus test system results are shown in thistable comparison for with out and with UPFCsystems. The active and reactive losses are reduced.

The total losses are compared with placing UPFC andwithout UPFC.

CONCLUSIONS

Equations which describe the losses minimization byusing power injection method are obtained. The mathlab results demonstrate the validity of the proposedUPFC model and the UPFC network-interfacingalgorithm. The total active and reactive power lossesare reduced. There by active power is improved due

to minimization of transmission losses in powersystem the transmission and distribution costs arereduced.

ACKNOWLEDGMENT

I express my sincere thanks to Sri.M.VenkateswaraRao, Associate professor, Head of Department, E.E.EDepartment of EEE, for his valuable guidance andsupervision throughout the project work.


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DIMINISHING OF LOSSES IN A TRANSMISSION LINE BY USING UPFC.pdf