FLEXIBLE AC TRANSMISSION SYSTEMS (FACTS)

WHAT IS FACTS ?

IEEE definition : “AC transmission systems incorporating power electronic based and other static controllers to enhance availability and to increase power transfer capabilities”

FACTS CONTROLLE

RS

Based on connection

Series controller

Shunt controller

Combined series series

controller

Combined series shunt controller

Based on type of

commutation

Natural

Forced

Based on switching frequency

Low frequency

Medium frequency

High frequency

Based on type of PE

device used

Variable impedance type (VIT)

Voltage source

converter (VSC)

SERIES CONTROLLERVariable impedance or

variable sourceInjects voltage in series

with the lineMore powerful

controllerFor active power controlImprove transient

stability of power system

SHUNT CONTROLLERSInjects current into a line

Variable impedance or source connected to the line

Improve dynamic stability

COMBINED SERIES SHUNT CONTROLLER

Inline power flow control

Unified power flow controller

COMBINED SERIES SERIES CONTROLLER

(B) CLASSIFICATION BASED ON COMMUTATION

Forced Commutation : GTO Natural commutation : SCR

(C) CLASSIFICATION BASED ON SWITCHING FRQUENCY

low frequency (50 – 60 Hz)

Medium frequency switching (100 – 500 Hz)

High frequency switching ( > 500 Hz)

(D) CLASSIFICATION BASED ON TYPE OF PE DEVCIE USED

VARIABLE IMPEDENCE TYPE(VIT) VOLTAGE SOURCE CONVERTER(VSC)

Consists of impedancesSupplies or absorbs reactive power

No voltage source

Eg: SVC, TCSC, TCPST etc.

Consists of a voltage sourceCompactCan supply active and reactive power

Eg: STATCOM, SSSC, UPFC etc.

IMPORTANT FACTS CONTROLLERS

SVC (Static var compensator)

STATCOM (Static Compensator)

SSSC (Static Synchronous Series Compensator)

UPFC (Unified Power Flow Controller)

STATIC VAR COMPENSATOR (SVC)Classification string: 1P-NC-LF-ZES-NDC

PF correction

Provides fast acting reactive power

Stabilization of bus bar voltage

Improve damping of dynamic oscillation

STATIC VAR COMPENSATOR (SVC)

TransformerSwitchgearReactorThyristor valvesCapacitor bankCooling systemControl and protection

STATIC SYNCHRONOUS COMPENSATOR(SSC) OR STATCOM

Classification string: 1P-FC-HF-CES-DC

For supplying reactive power

Active power control is possible

Quick response

Less space

STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

Classification string: 1S-FC-HF-CES-DC

Exchange both active and reactive power

Compensate drop due to reactive and resistance losses

Maintains constant X/R ratio

UNIFIED POWER FLOW CONTROLLER (UPFC)Classification string: 2-FC-HF-CES-DC

Combination of STATCOM and SSSC

Control both active and reactive power

Provides high flexibilityTerminal voltage controlPhase angle regulationSeries line compensation

ADVANTAGES OF FACTS

Power transmission capabilitySystem stability Power qualityEnvironmental impactTransmission lossesDynamic and reactive power support and voltage

controlDynamic oscillation in power system

CONCLUSIONFACTS is an application of power electronics in

transmission systemFACTS controllers makes a system ‘flexible’FACTS controllers are classified based on connection,

commutation etc.SVC, STATCOM, UPFC etc have a number of applications

in power systemsFACTS has an important role in active and reactive power

controlFACTS helps to improve the capacity of an existing systemFACTS controllers improve the power quality and stability

REFERENCESW.N. Chang and C.J. Wu, “Developing static

reactive power compensator in a power system”, IEEE Trans. on Power Systems

K.R. Padiyar and R.K. Varma, “Damping torque analysis of static VAR system controllers”, IEEE Trans. on Power Systems,

N.G.. Hingorani, “Flexible ac transmission”, IEEE Spectrum, pp. 40–45

Power Semiconductor Devices and Circuits, Brown Boveri symposia series, Baden Datettwil

QUESTIONS?

THANK YOU