This document discusses flexible alternating current transmission systems (FACTS) and focuses on shunt compensators. It covers the objectives of shunt compensation including midpoint voltage regulation to segment transmission lines, end of line voltage support to prevent instability, improving transient stability, and damping power oscillations. Midpoint compensation regulates voltage to allow lines to be treated as multiple segments. End of line support maintains receiving end voltages and prevents instability during disturbances. Shunt devices provide fast reactive power to damp out angle and power oscillations following events. The document examines these topics through mathematical analysis and diagrams.

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FLEXIBLE ALTERNATING CURRENT
TRANSMISSION SYSTEMS
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Presented By :
HARI MADHAVA REDDY. Y (Ph.D)., M.Tech
Assistant professor
UNIVERSAL COLLEGE OF
ENGINEERING AND TCHNOLOGY
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

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Contents
Unit–I: Introduction to FACTS
Unit–II: Voltage source and Current source converters
Unit–III: Shunt Compensators–1
Unit–IV: Shunt Compensators–2
Unit V: Series Compensators
Unit–VI: Combined Controllers

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Learning Objectives
 To learn the basics of power flow control in transmission
lines using FACTS controllers
 To explain operation and control of voltage source converter.
 To understand compensation methods to improve stability
and reduce power oscillations of a power system.
 To learn the method of shunt compensation using static VAR
compensators.
 To learn the methods of compensation using series compensators
 To explain operation of Unified Power Flow Controller (UPFC).

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Learning Outcomes
 Understand power flow control in transmission lines using FACTS
controllers.
 Explain operation and control of voltage source converter.
 Analyze compensation methods to improve stability and reduce
power oscillations in the transmission lines.
 Explain the method of shunt compensation using static VAR
compensators.
 Understand the methods of compensations using series
compensators.
 Explain operation of Unified Power Flow Controller (UPFC).

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Text Books:
1. “Understanding FACTS” N.G.Hingorani and L.Guygi, IEEE
Press.Indian Edition is available:––Standard Publications, 2001.
Reference Books:
1. “Flexible ac transmission system (FACTS)” Edited by Yong Hue
Song and Allan T Johns, Institution of Electrical Engineers,
London.
2. Thyristor-based FACTS Controllers for Electrical Transmission
Systems, by R.MohanMathur and Rajiv k.Varma, Wiley

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Unit–I:
Introduction to FACTS
Power flow in an AC System – Loading capability limits – Dynamic
stability considerations – Importance of controllable parameters – Basic
types of FACTS controllers – Benefits from FACTS controllers –
Requirements and characteristics of high power devices – Voltage and
current rating – Losses and speed of switching – Parameter trade–off
devices.
Unit–II:
Voltage source and Current source converters
Concept of voltage source converter(VSC) – Single phase bridge
converter – Square–wave
voltage harmonics for a single–phase bridge converter – Three–phase
full wave bridge converter– Three–phase current source converter –
Comparison of current source converter with voltage source converter.

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Unit–III:
Shunt Compensators–1
Objectives of shunt compensation – Mid–point voltage regulation for
line segmentation – End of line voltage support to prevent voltage
instability – Improvement of transient stability– Power oscillation
damping.
Unit–IV:
Shunt Compensators–2
Thyristor Switched Capacitor(TSC)–Thyristor Switched Capacitor
– Thyristor Switched Reactor (TSC–TCR). Static VAR
compensator(SVC) and Static Compensator(STATCOM): The
regulation and slope transfer function and dynamic performance –
Transient stability enhancement and power oscillation damping–
Operating point control and summary of compensation control.

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Unit–III
Shunt Compensators–1
3.1. Objectives of shunt compensation
3.2. Mid–point voltage regulation for line segmentation
3.3. End of line voltage support to prevent voltage instability
3.4. Improvement of transient stability
3.5. Power oscillation damping.

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3.1. OBJECTIVES OF SHUNT COMPENSATION

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The ultimate objective of applying reactive shunt compensation in a
transmission system is to increase the transmittable power. This may
be required to improve the steady-state transmission characteristics
as well as the stability of the system. Var compensation is thus used
for voltage regulation at the midpoint (or some intermediate) to
segment the transmission line and at the end of the (radial) line to
prevent voltage instability, as well as for dynamic voltage control to
increase transient stability and "damp power oscillations.
basic considerations to increase the transmittable power by ideal
shunt-connected var compensation will be reviewed in order to
provide a foundation for power electronics-based compensation
and control techniques to meet specific compensation objectives.

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3.2. Midpoint Voltage Regulation for Line Segmentation

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3.3. End of Line Voltage Support to Prevent Voltage Instability

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3.4. Improvement of Transient Stability
Reactive shunt compensation can significantly increase the
maximum transmittable power. Thus, it is reasonable to expect that,
with suitable and fast controls, shunt compensation will be able to
change the power flow in the system during and following dynamic
disturbances so as to increase the transient stability limit and provide
effective power oscillation damping.
The potential effectiveness of shunt on transient stability
improvement can be conveniently evaluated by the equal area
criterion. The meaning of the equal area criterion is explained with
the aid of the simple two machine (the receiving end is an infinite
bus), two line system the corresponding P versus δ curves shown in
Figure .

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The shunt compensator is assumed to be ideal means that the
amplitude of the midpoint voltage remains constant all the time,
except possibly during faults, and its phase angle follows the
generator angle swings so that the compensator would not be
involved in real power exchange, but it would continuously
provide the necessary reactive power.

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Figure shows, the reactive power demand on the midpoint
compensator increases rapidly with increasing power transmission,
reaching a maximum value equal to four per unit at the maximum
steady-state real power transmission limit of two per unit.

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3.5 Power Oscillation Damping
An under-damped power system, any minor disturbance can
cause the machine angle to oscillate around its steady-state value at the
natural frequency of the total electromechanical system. The angle
oscillation, of course, results in a corresponding power oscillation
around the steady-state power transmitted.
The lack of sufficient damping can be a major problem in some
power systems and, in some cases, it may be the limiting factor for the
transmittable power.

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Summary of Compensator Requirements