This document provides an introduction to Flexible AC Transmission Systems (FACTS). It discusses why transmission interconnections are needed, including to minimize generation and fuel costs and supply electricity at minimum cost. It also explores if the full potential of interconnections can be used and describes opportunities for FACTS technology to control power flow and enhance transmission line usage. Some key limitations on transmission line loading capability like thermal, dielectric, and stability limits are also summarized.

1. An Introduction to FACTS
Presented by
T.S.L.V.Ayyarao
Assistant Pofessor
GMRIT

2. Why do we need Transmission Interconnections?
 Delivery of Electrical Power
 To minimize the total power generation capacity
and Fuel cost.
 To supply electricity to the loads at minimum cost
with a required reliability.
 Transmission is an alternative to a new generation
resource.
 Economic energy or reserve sharing is constrained
by transmission capacity

3. Why do we need Transmission Interconnections?
Can we use the full potential of Transmission
interconnections?
 As power transfers grow, the system becomes
more complex to operate.
 The power systems of today are mechanically
controlled
If so what?
 Switching devices are mechanical and there is
little high speed
 Mechanical devices cannot be initiated frequently.

4. Why do we need Transmission Interconnections?
 Mechanical devices wear out quickly.
 In view point of both dynamic and steady state
operation, the system is really uncontrolled.
 In recent years, power demand increases day by
day.
 Increased demand and absence of long term
planning leads to less security and reduced quality
of supply.

5. Opportunities for FACTS
FACTS technology opens up opportunities to control
power and enhance the usage capability of line
FACTS controller uses
 Control the current through the line at reasonable
cost.
 Enables the power to flow under normal and
contingency conditions
 To control the interrelated parameters (series
impedance, shunt impedance, current, voltage,
phase angle)

6. Opportunities for FACTS
 To damp oscillations at various frequencies below
rated frequency.
 Enable a line to carry power closer to its thermal
rating.
 Mechanical switching replaced with power
electronics

7. Power Flow in an AC System
 In ac system, the electrical generation and load
must balance at all times.
 The electrical system is self-regulating.
 If generation is less than load, voltage and
frequency drop.
 Active power flows from surplus generation areas
to deficit areas.

8. Power Flow in Parallel Paths

9. Power Flow in a Meshed System

10. Power Flow in a Meshed System
 A adjustable series capacitor controls the power
flow
 Mechanically switched series capacitor is limited
by wear and tear.
 A series capacitor in a line may lead to
subsynchronous resonance.
 This occurs when mechanical resonance
frequencies of the shaft of a multiple turbine
generator unit coincides with 50hz minus the
electrical frequency of the line.

11. Power Flow in a Meshed System
If series capacitor is thyristor controlled
 It can be varied as often as required
 Rapidly damp any sub-synchronous resonance
conditions
 Damp low frequency oscillations in the power
flow
 Avoid risk of damage to generator shaft and
system collapse
 Greatly enhance stability of the network.

12. Limitations of loading capability
 For best use of transmission asset and to maximize
the loading capability, what are the limitations?
There are three kinds of limitations
 Thermal
 Dielectric
 Stability

13. Limitations of loading capability
 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 over-
voltage and power flow conditions.

14. Limitations of loading capability
 Stability
The stability issues that limit the transmission capability
include:
1. Transient stability, dynamic stability, steady-state
stability, frequency collapse. Voltage collapse, and
sub-synchronous resonance.
2. The FACTS technology can certainly be used to
overcome any of the stability limits.