This document discusses the need for transmission interconnections and opportunities provided by FACTS (Flexible AC Transmission Systems) technology. It notes that India has generation surpluses in some grids but deficits in others, and interconnections allow sharing of power to reduce costs. FACTS devices can control power flows and enhance line capacity, enabling more economic energy transfers. They offer advantages over mechanical switching like reduced wear and ability to damp oscillations. FACTS technology opens opportunities to better utilize transmission assets by overcoming thermal, dielectric and stability limitations on line loadings.

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

2. Why do we need Transmission Interconnections?

3. Why do we need Transmission Interconnections?
 India has an abundance of generation in the
Eastern and North-Eastern grids, primarily coal.
 But the other three grids are in deficit at peak
periods, regardless of season.
 Potentially significant swings in demand in the
Northern or Southern grids could quickly upset the
balance

4. Why do we need Transmission Interconnections?

5. 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

6. 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.

7. 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.

8. Opportunities for FACTS
FACTS technology opens up opportunities to control
power and enhance the usage capability of line
 The current through the line can be controlled at
reasonable cost.
 Thus existing capacity of transmission lines can be
enhanced (opportunity).
Facts Controller
 Enables the power to flow under normal &
contingency conditions
 Control the interrelated parameters (series
impedance, shunt impedance, current, voltage, etc)

9. Opportunities for FACTS
 Damp oscillations at various frequencies below
rated frequency.
 Enable a line to carry power closer to its thermal
rating.
 These constraints cannot be overcome by
mechanical means without lowering transmission
capacity of line.
 Mechanical switching replaced with power
electronics

10. Opportunities for FACTS
 FACTS technology is not a single high power
controller.
 This technology needs incremental investment and
enhances transmission capacity step by step.
 Cost of FACTS controller are declining day by
day.

11. 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.

12. Power Flow in Parallel Paths

13. Power Flow in a Meshed System

14. 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.

15. 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.

16. 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

17. 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.

18. 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.