How FACTS Controllers How FACTS Controllers BenefitBenefit

AC Transmission SystemsAC Transmission Systems

ByBy

P.Narsimha reddyP.Narsimha reddy

1005-10-7432051005-10-743205

ContentsContents

IntroductionIntroduction Why FACTS Controllers Why FACTS Controllers Power System ConstraintsPower System Constraints Controllability of Power SystemsControllability of Power Systems Examples of conventional& Examples of conventional& FACTS Controllers FACTS Controllers Comparison of FACTS & conventional cktsComparison of FACTS & conventional ckts Benefits of Control of Power SystemsBenefits of Control of Power Systems Overview of FACTS Controllers cktsOverview of FACTS Controllers ckts

IntroductionIntroduction

To achieve both operational reliability and financial To achieve both operational reliability and financial profitability, it has become clear that more efficient profitability, it has become clear that more efficient utilization and control of the utilization and control of the existing existing transmission transmission system infrastructure is required.system infrastructure is required.

In the evolving utility environment, financial and In the evolving utility environment, financial and market forces are, and will continue to, demand a market forces are, and will continue to, demand a more optimal and profitable operation of the power more optimal and profitable operation of the power system with respect to generation, transmission, system with respect to generation, transmission, and distributionand distribution

Why FACTS Controllers requiredWhy FACTS Controllers required

The process to permit, site, and construct new The process to permit, site, and construct new transmission lines has become extremely difficult, transmission lines has become extremely difficult, expensive, time-consuming, and expensive, time-consuming, and controversialcontroversial. .

FACTS technologies provide advanced solutions as FACTS technologies provide advanced solutions as cost-effective alternatives to new transmission line cost-effective alternatives to new transmission line constructionconstruction

Power System ConstraintsPower System Constraints

Steady-State Power Transfer Limit Steady-State Power Transfer Limit Voltage Stability Limit Voltage Stability Limit Dynamic Voltage Limit Dynamic Voltage Limit Transient Stability Limit Transient Stability Limit Power System Oscillation Damping Limit Power System Oscillation Damping Limit Inadvertent Loop Flow Limit Inadvertent Loop Flow Limit Thermal Limit Thermal Limit Short-Circuit Current Limit Short-Circuit Current Limit Others Others

Controllability of Power SystemsControllability of Power Systems

Power system only has certain variables that Power system only has certain variables that can be impacted by control, consider the basic can be impacted by control, consider the basic and well-known power-angle curveand well-known power-angle curve

AngleAngle VoltageVoltage ImpedanceImpedance

Examples of conventional equipment Examples of conventional equipment for enhancingfor enhancing

Series Capacitor Controls impedanceSeries Capacitor Controls impedance

Switched Shunt-Capacitor and Reactor Switched Shunt-Capacitor and Reactor -Controls voltage -Controls voltage

Transformer LTC -Controls voltageTransformer LTC -Controls voltage

Phase Shifting Transformer -Controls Phase Shifting Transformer -Controls angle angle

Synchronous Condenser -Controls voltageSynchronous Condenser -Controls voltage, ,

Example of FACTS controllers for Example of FACTS controllers for enhancing power system enhancing power system control control

Static Var Compensator (SVC)Static Var Compensator (SVC) Controls voltageControls voltage

Unified Power Flow Controller (UPFC) Unified Power Flow Controller (UPFC)

Convertible Static Compensator (CSC)Convertible Static Compensator (CSC) Inter-phase Power Flow Controller (IPFC) Inter-phase Power Flow Controller (IPFC)

Thyristor Controlled Series Compensator (TCSC) -Controls impedance

Thyristor Controlled Phase Shifting Transformer (TCPST) -Controls angle

Static Synchronous Series Controller (SSSC) -controllers impact voltage, impedance, and/or angle

Static Synchronous Compensator (STATCOM) -Controls voltage

Comparison of FACTS & conventional ckts

This figure shows that the speed of mechanical switches, can be as fast as a couple of cycles of 60 (or 50) Hz.

This speed of switching in and of itself may be fast enough to solve many power system constraints.

Although there is a vast improvement in switching time from mechanical to power electronic based solutions

The main benefit that FACTS controller solutions provide is the “cycling/repeatability” and “smooth control”

Benefits of Control of Power Systems

Increased Loading and More Effective Use of Transmission Corridors

Added Power Flow Control Improved Power System Stability Increased System Security Increased System Reliability Added Flexibility in Siting New Generation

Overview of FACTS Controllers ckts

Static Var Compensator (SVC)Static Var Compensator (SVC)

Controls voltageControls voltage

Static Synchronous Compensator (STATCOM) -Controls voltage

Unified Power Flow Controller (UPFC) Unified Power Flow Controller (UPFC)

impedence, voltage magnitude and phase angle

svc

In general, the two thyristor valve controlled/switched concepts used with SVCs

The thyristor-controlled reactor (TCR) and the thyristor-switched capacitor (TSC).

The TSC provides a “stepped” response and the TCR provides a “smooth” or continuously variable susceptance

The SVC regulates voltage at its terminals by controlling the amount of reactive power injected into or absorbed from the power system.

When system voltageis low, the SVC generates reactive power (SVC capacitive). When system voltage is high, it absorbs reactive power (SVC

inductive).

The variation of reactive power is performed by switching three-phase capacitor banks and inductor banks connected on the secondary side of a coupling transformer

Each capacitor bank is switched on and off by three thyristor switches (Thyristor Switched Capacitor or TSC).

Reactors are either switched on-off (Thyristor Switched Reactor or TSR) or phase-controlled (Thyristor Controlled Reactor or TCR).

STATCOM

The function of a STATCOM is similar to that ofa synchronous condensor.

In general it provides reactive power compensation to solve a variety of power system, voltage fluctuation and stablity conditions

STATCOM consists of

DC voltage sourse, gate commutated turn off thyristors(GCT), step up transformers

Operation mode

Unified Power Flow Controller Unified Power Flow Controller (UPFC)(UPFC)

The universal and most flexible FACTS device is the Unified Power Flow Controller (UPFC).

UPFC is the combination of three compensators’ characteristic; i.e. impedence, voltage magnitude and phase angle.

Basic ckt diagram

UPFC construction

The UPFC consists of two voltage source converters; series and shunt converter, which are connected to each other with a common dc link.

Series converter or Static Synchronous Series Compensator (SSSC) is used to add controlled voltage magnitude and phase angle in series with the line.

while shunt converter or Static Synchronous Compensator (STATCOM) is used to provide reactive power to the ac system, beside that, it will provide the dc power required for both inverter.

The energy storing capacity of this dc capacitor is generally small.

Therefore, active power drawn by the shunt converter should be equal to the active power generated by the series converter.

The reactive power in the shunt or series converter can be chosen independently, giving greater flexibility to the power flow control.

Control of power flow is achieved by adding the series voltage, VS with a certain amplitude, VS and phase shift, φ to V1.

This will gives a new line voltage V2 with different magnitude and phase shift.

As the angle φ varies, the phase shift δ between V2 and VR also varies.

Conclusion

In power system transmission, it is desirable to maintain the voltage magnitude, phase angle and line impedance. Therefore, to control the power from one end to another end, this concept of voltage injection is applied.

References S. Mori, K. Matsuno, T. Hasegawa, S. Ohnishi,

“Development of a Large Static Var Generator Using Self-Commutated Inverters for Improving Power System Stability,” IEEE Transactions, 1993

N. Morishima, Takeda, T. Sugiyama, Y. Hamazaki, T. Snow, A. Abed, “SDG&E Talega STATCOM Project - System Analysis, Design, and Configuration,” Proceedings of the IEEE PES, October 2002.