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?
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