13-08-2012, 04:23 PM
FLEXIBLE AC TRANSMISSION SYSTEMS
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INTRODUCTION
The FACTS technology is a collection of controllers, which
can be applied individually or in coordination with others to
control one or more of the interrelated system parameters,
such as series impedance, shunt impedance, current,
voltage, and damping of oscillations.
GENERATIONS:-
• 1st Generation of FACTS (SVC & TCSC).
• 2nd Generation of FACTS (STATCOM & SSSC).
• 3rd Generation of FACTS (UPFC & IPFC).
What is the Need?
Thermal
For overhead line, thermal capability is a function of ambient
temperature, wind conditions, conditions of conductor, and ground
clearance.
The FACTS technology can help in making an effective used of
newfound line capability.
Dielectric
Being designed very conservatively, most lines can increase
operation voltage by 10% or even higher.
FACTS technology could be used to ensure acceptable overvoltage
and power flow conditions.
Stability
The stability issues that limit the transmission capability include:
transient stability, dynamic stability, steady-state stability,
frequency collapse. Voltage collapse, and sub-synchronous
resonance.
The FACTS technology can certainly be used to overcome any of
the stability limits.
LIMITATIONS OF LARGE AC SYSTEMS
(LONG DISTANCE
TRANSMISSION SYSTEMS)
• Voltage stability
• Reactive power problems
• Steady state stability
• Transient Stability
(INTERCONNECTED
SYSTEMS)
• Load Flow Problems
(needs management of
Congestion)
• Voltage Stability
• Frequency Control
• Oscillation Stability
• Inter-Area Oscillations
ADVANTAGES of FACTS
Increase of Power Transfer without adding new
transmission lines.
Transmission Cost minimization.
Steady state and dynamic voltage control.
Improvement of System Stability and Voltage
quality.
Active damping of Oscillations.
BASIC TYPE OF FACTS CONTROLLERS
Series controllers:
The series controller could be a variable impedance or a variable source
both are power electronics based. In principle, all series controllers inject
voltage in series with the line.
Shunt controllers:
The shunt controllers may be variable impedance connected to the line
voltage causes a variable current flow hence represents injection of current
into the line.
Combined series-series controllers:
The combination could be separate series controllers or unified seriesseries
controller--- Interline Power Flow Controller.
Combined series-shunt controllers:
The combination could be separated series and shunt controllers or a
unified power flow controller.