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ADVANCE FLEXIBLE AC TRANSMISSION SYSTEM

PREMANSHU SHEKHARUSN-1DS07EE059

‘8’A

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Flexible AC Transmission System

Alternating current transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability

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• With the ongoing expansion and growth of the electric utility industry, including deregulation in many countries, numerous changes are continuously being introduced

INTRODUCTION

• Transmission systems are being pushed closer to their stability and thermal limits while the focus on the quality of power delivered

• Demand due to optimal and profitable operation of the power system with respect to generation, transmission, and distribution.

• More efficient utilization and control of the existing transmission system infrastructure is required.

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• Improved utilization of the existing power system is provided through the application of advanced control technologies. Power electronics based equipment, or Flexible AC Transmission Systems (FACTS),

• The process to permit, site, and construct new transmission lines has become extremely 1. Difficult2. expensive3. time-consuming4. controversial.

• FACTS technologies provide advanced solutions as cost-effective alternatives to new transmission line construction.

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CONTROL OF POWER SYSTEM

It can be divided into three types.

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Constraints on Useable Transmission Capacity

Dynamic:Transient and dynamic stabilitySubsynchronous oscillationsDynamic overvoltages and undervoltagesVoltage collapseFrequency collapse

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Steady-State:Uneven power flowExcess reactive power flowsVoltage capabilityThermal capability

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POWER FLOW IN TRANSMISSION LINE

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jXSV RV

SRP

sinS RSR

V VP

X

Power flow in a transmission line

To increase PSR, increase

and R SV V jXI

jXI

SV

RV

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AV BVinjV- +

AVinjV

BV

jXSV RV

SRP

RV injV- + sinS RSR

V VP

X

jXIinjV

SV

RV

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FACTS ControllersStatic VAR Compensator - SVCThyristor Controlled Series Compensator -

TCSCThyristor Controlled Phase Angle Regulator -

TCPARStatic Synchronous Compensator - StatComSolid State Series Compensator - SSSCUnified Power Flow Controller - UPFC

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SVC - Static Var Compensator (Standard for Parallel Compensation):

 Among the FACTS controllers, Static Ver. Compensator (SVC) provides fast acting dynamic reactive compensation for voltage support during contingency events

SVC also dampens power swings and reduces system losses by optimized reactive power control.

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SVC is built up with reactors and capacitors, controlled by thyristor valves which are in parallel with a fixed capacitor bank. It is connected in shunt with the transmission line through a shunt transformer

ADVANTAGES

The main advantage of SVCs over simple mechanically-switched compensation schemes is their near-instantaneous response to changes in the system voltage  cheaper, higher-capacity, faster more reliable than dynamic compensation schemes such as synchronous condensers.

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STATCOM-Static Synchr. Compensator (Fast SVC, Flicker Compensation):

STATCOM is defined by IEEE as a self commutated switching power converter supplied from an appropriate electric energy source and operated to produce a set of adjustable multiphase voltage, which may be coupled to an AC power system for the purpose of exchanging independently controllable real and reactive power.

The controlled reactive compensation in electric power system is usually achieved with the variant STATCOM configurations.

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Basic statcom

ADVANTAGES

• The steady state loadability of the line is improved

• The voltage rise due to capacitance switching is subtantially reduced both in magnitude and duration

• Voltage variation due to consumer’s loading is reduced

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Advance Thyristor Controlled Series Compensator - ACSC

Thyristor-Controlled Series Capacitors offer a strong alternative for optimizing of transmission over power links, existing as well as new, by means of increased dynamic stability, power oscillation damping as well as optimized load flow between parallel circuits.

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Series compensation has been utilized for many years with excellent results in AC power transmission in a number of countries all over the world.

It can be demonstrated by well-known expressions relating to active power transfer and voltage:

Here, V1 and V2 denote the voltages at either end of the interconnection, whereas Ψ denotes the angular difference of the said voltages. X is the reactance of the transmission circuit, while P and Q denote the active and reactive power flow.

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Active power can be increased by decreasing the effective series reactance of the line.

overall power transmission capacity increase

the reactive power contribution from a capacitive element in series with the line acts to improve the reactive power balance of the circuit, and thereby to bring about a stabilization of the transmission voltage.

This reactive power contribution is instantaneous and of a self- regulatory nature.

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UPFC

may control voltage, impedance, and angle

impacts active and reactive power flow in line

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Basic OperationBasic Operation

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UPFC CapabilitiesUPFC CapabilitiesIncrease transmission line capacityDirect power flow along selected linesPowerful system oscillation dampingVoltage support and regulationControl of active and reactive power flow at

both sending- and receiving-end

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OperationOperation

Reactive power is generated or absorbed by the shunt inverter to control bus voltage

Reactive power is generated or absorbed by the series inverter to control the real and/or reactive power flow on the transmission line

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ADVANTAGES OF FACTS

• Improved power transmission capability • Improved system stability and availability • Improved power quality • Minimized environmental impact • Minimized transmission losses 

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CONCLUSION

•The controlled static compensator is configured to regulate the terminal voltage with certain degree of accuracy. Herein it has been also observed that the transient stability can be increased by maintaining the transmission voltage at midpoint. This can be further enhanced by temporarily increasing the voltage above the regulation reference. • The SVC will reciprocate with same features but limited transient stability, which also depend SVC operational components. The instrumental approach to regulate the voltage and system stability were exceptional by using STATCOM and SVC controllers, which are showing how voltage control would improve the power system quality.

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REFRENCES [1]. How FACTS controllers benefits AC transmission systems: John J. Paserba, Fellow IEEE. [2]. How FACTS improve the performance of electrical grid: Rolf Grunbaum, Ake Petersson, Bjom Thorvaldsson (ABB Review 3/2002) [3]. Dynamical performance of TCSC schemes: By Lennart Angquist,Gunnar Ingestrom, Hans-Ake Jonsson ABB Power system AB Sweden (CIGRE 1996:14-302) [4]. Application of STATECOM for damping torsional oscillation in series compensated AC systems: By K.V Patil, J. Senthil, J.Jiang R.M.Mathur:: IEEE Transactions on energy conversion, Vo.,13 No. 3, September 1998.

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