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PRESENTEDBY, P.NARAYANA SWAMY, M.RAJASEKHAR.

ABSTRACT P.V.K

-2FACTS Energy is the basic necessity for the economic development of the country. The rate of growth of electricity usage through out the world is increasingly high in the last ten years. In recent years ecological concern and high installation costs have put constraints over construction over head lines in many countries; there by forcing existing to be used more efficiently & effectively. AC transmission systems are thought of as being inflexible. This paper presents a new approach for realizing a smart, fault tolerant, controllable and asset efficient power grid through the use of massively manufactured communications-enabled sensors, power converter and actuator networks. One example is ‘Smart wires’ implemented using many modules of a unified power flow controller (UPFC) device that can be clamped on a existing power lines, and can be operated so as to control the impedance of the conducters, reactive power-thus controlling power flow. This approach promises important system-wide benefits includingincreased line and system capacity; increased reliability; improved asset utilization; improved operation under contingencies; reduced environmental impact; incremental deployment; and rapid implementation.

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INTRODUCTION The need to augment existing transmission network is overdue as networks have not grown commensurate to generation. This has become particular series after introduction of independent power produces (IPP) & capacitive generation (CG) are connected to the existing networks. There is a need to review border aspects of planning transmission systems the need to have better discipline and control over the system to cater to network constraints on one hand to stringent requirements of the consumer on the other. The use of newer technology available today including solid state devices such as FACTS, which are entering the power sector, have also to be considered in any future planning/augmentation studies. One must study existing practice in system improvement and various limitations as also the interim measures required to increase the T&D systems capability.

FACTS DEVICES AND APPLICATIONS P.V.K

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S. DEVICE DESCRIPTION APPLICATION NO thyristor switch Reactive power control 1. Static VAR compensator Fast controlling a shunt and voltage support 2.

Thyristor control series capacitor (TCSC) Static phase shifter(SPS)

3. 4. 5.

capacitor and reactor SCR is used to control capacitor bank connected in series with a line

Thyristor connected to secondary of transformer is used to add or subtract voltage in qadrature to the system voltage Static synchronous Advanced configuration compensator-condenser of gate turn-off thyristors (STATCOM/STATCON) (GTO) is used with out the need for large external circuit elements Unified power flow Combination of control (UPFC) STATCOM and SSSC for injecting controlled voltage of controlled phase angle in series with the line

To control line impendence And improve transfer on lines To control power flow in lines

Fast and precise reactive power control and voltage support can act quickly to damp major disturbances in the power system Provides means to independent control of the active and reactive power, as well as control of line to ground voltage

UNIFIED POWER FLOW CONTROLLER: P.V.K

-5FACTS Gyugini proposed the unified power flow controller (UPFC) concept in 1991. The was designed for the real time control and dynamic compensation of A.C transmission systems, providing multi functioning flexibility required to solve many of the problems facing the delivery industry. With in the frame work of traditional power transmission concepts, the UPFC is able to control, simultaneously are selectively, all the parameters effecting the power flow in the transmission line (i.e. voltage, impedance phase angle) and this unique capability is signified by the adjective “UNIFIED” in the name. Alternatively, it can independently control both the real and reactive power flows in the line. The unified power flow controller is a member of this later family of compensator and power flow controllers that utilize the synchronous voltage source (SVS) concept for providing a uniquely comprehensive capability for transmission control. These basic capabilities make the UPFC most powerful device presently available for transmission control.

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CIRCUIT ARRANGMENT:

In the presently used practice implementation the UPFC consists of two switching converters, which in the implementations considered are voltage source inverters using gate turn-off (GTO) thyristor valves. These back to back converters i.e. “converter A” & “converter B”, are operated from a common D.C link provided by a D.C storage capacitor this arrangement functions as an A.C to A.C power converter in which the real power can freely flow in either direction between the A.C terminals of the two converters and each converter can independently generate or absorb reactive power as its own A.C out put terminals.

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BASIC CONTROL FUNCTIONS:Operation of UPFC from the stand point of conventional power transmission based on reactive shunt compensation, series compensation, and phase angle shifting, the UPFC can fulfill these functions and there by meet multiple control objectives by adding the injected voltage Vpq, with appropriate amplitude and phase angle, to the terminal voltage Vo. Using phasor representation, the basic UPFC power flow control functions are illustrated in the figure. TERMINAL VOLTAGE REGULATION: - similar to that obtained with a transformer tap-changer having infinitely small steps. Vpq=&v is injected in phase or anti phase with Vo. Series capacitor compensation Vpq=Vc is in qudrature with the line current. Transmission angle regulation (phase shifting) Where Vpq=Vo injected with angular relationship with respect to Vo that achieves the desired s phase shift (advance or retard) without any change in magnitude. Multifunctional power flow control, Executed by simultaneous terminal voltage regulation, series capacitive compensation, and phase shifting, Vpq=&V+Vc+Vo.

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BASIC OPERATING PRINCIPLES AND CHARACTERSTICS:

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The UPFC was designed for a real time control of dynamic Compensation of A.C transmission systems providing multi functioning capability i.e. required to solve many of the problems facing power delivery industry. UPFC is a generalized synchronous voltage source (SVS) represented with the fundamental frequency by voltage source Vpq with controllable magnitude (0
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- 11 FACTS UPFC arrangements the real power SVS exchange is provided by one end of the bus and indicated in the figure. In the presently used practical considerations the UPFC consists of two-voltage source converts using Gate turn off thyristor (GTO). The converter labeled converter 1 & converter 2 in the figure operated from a common D.C link provided by storage capacitor. This functions as an ideal ac to ac power converter in which the real power can freely flow in any direction between the A.C terminals of the two converters and each converter can independently generate (absorb) reactive power as its own terminals. Converter 2 provides the main function of the UPFC by injecting voltage Vpq and phage angle P in series with the line via an injecting transformer. This injected voltage acts an synchronously ac voltage source. The transmission line current flows through this voltage source resulting in real and reactive power exchanged between it and the ac system. The converter generates the reactive power exchanged at the ac terminal internally. The real power exchanged is converted into DC power, which appears at the DC link as positive or negative real power demand. The basic function of the converter is to supply or absorb the real power demand by converter 2 at the common DC link. This DC link power is converted into ac and coupled to the transmission line via a shunt-connected transformer. Converter1can also generate or absorb controllable reactive power. if it is desired and provide independent control of the line. It is important to note that where as there is closed direct path for the real power negotiated by the action of series voltage injection through converter 1&2 back to the line, the corresponding reactive power exchanged is supplied or absorb by the converter and therefore does not have a reactive power exchange with the line independent of the reactive power exchanged by the converter 2. This means that there is no reactive power flow through the UPFC.

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CONTROL OF UPFC: It is a well known that shunt reactive power injection can be used to control bus voltage. The shunt current Ish is split into two components: a reactive current Ishq in quadrature with bus voltage and a real current Ishq is controlled to regulate the voltage magnitude at port1 of the UPFC as proposed for the STATCOM. The voltage reference of the voltage regulator can be varied slowly to meet the study state reactive power requirements. The reference value for the shunt current Ishp is set so that the capacitor voltage is regulated. The series injected voltage can be controlled to meet required P&Q demand in the line. Power oscillations damping is also achieved by varying only the reactive power flow in the series branch. One approach to control the series injected voltage is to split injected voltage, which will mainly affect the reactive power in quadrature with the sending end voltage, which mainly effects active power. These two components can be

controlled to meet the required power demand in the lines. This control scheme requires either telemetry or synthesis of the sending end voltage angle unless the UPFC is located near the bus whose voltage signal is utilized. An alternative to using either the sending end or receiving end voltage reference is use the line current as the reference the series injected voltage Vse can be split into two components: one component of magnitude Vsep and in phase with the line current and other components of magnitude Vseq in quadrature with the current. The advantage of using the current reference is that it is a locally measurable quantity. The controllable is designed to control scheme is aimed at damping the power swings and maintaining the stability after a disturbance.

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- 13 FACTS The voltages at the two ports of the UPFC are V1 and V2, Vr is the receiving end voltage and the series injected voltage is represented by two voltage sources of magnitudes Vsep& Vseq as mentioned above. Injecting a voltage in quadrature with the line current is equivalent to inserting a reactance in the line. Since the line current varies injecting a constant voltage in quadrature, actually introduces a variable reactance inserted in series with the line. If a resistor is inserted in a loss less line the sending power will have to supply the receiving end power loss in the resistor the UPFC on the other hand does not absorb or generate any real power. Therefore injecting a voltage in series, which is inphase with the line current, will not result in any active loss or gain and hence the sending end power is same as the receiving end power. Hence the power angle curve with voltage injections is different from the power angle curve that would be obtained by inserting a series resistor.

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MAJOR BENEFITS OF FACTS: COST: - due to the high capital cost of transmission plan, cost consideration frequently out weigh all other considerations. Compared to alternate methods of solving transmission loading problems FACTS technology often the most economic alternatives. CONVENIENCE: - all FACTS devices can be retrofitted to existing AC transmission plant with varying degrees of ease. Compared to HVDC or six phase transmission schemes, solutions can be provided with out wide scale system disruption and within a tine scale. ENVIRONMENTAL: - In order to provide new transmission route to supply an ever increasing world wide demand for electrical power, it is necessary to acquire the right to convey electrical energy over a given route. It is common for environmental opposition to frustrate attempts to establish new transmission route. FACTS technology, however allows grater through put over exisisting routes, thus transmission lines. However, the environmental impact of FATCS device itself may be considerable. In particular, series compensation units can be visually obtrusive with large items of transmission equipments placed on top of high voltage insulated platforms.

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BIBLOGRAPHY 1. N.G. Hingorani, L.Gyugyi “Under standing facts –concept and technology of flexible AC transmission systems”. 2. L.Gyugyi “unified power flow concept for Flexible AC transmission systems” 3. Dr. R. sreeram Kumar “Flexible AC transmission systems-an introduction” 4. A. Deepak devan (ATLANTA university) paper presentation. 5. Anjan havanur, U.K. Hambrade, “Active and Reactive power management in transmission system”.

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