FACTS_PPT.pptx.pdf of documentation fact

Outlines general facts

1. FLEXIBLE AC TRANSMISSION
SYSTEMS

2. What is FACTS?

•FACTS are power electronic based devices which improves the
controllability and stability of system.
•Flexible alternating current transmission system (FACTS) controllers
are capable of controlling power flows and enhancing the usable
capacity of existing transmission lines.

3. Need for FACTS devices
•To control the reactive power FACTS devices are needed
•For improving power factor
•It helps in increasing stability of system
•To enhance the quality of supply
•Includes financial benefits

4. Benefits of FACTS
•Increased transmission system reliability
•Better utilization of existing power transmission system
•It damp out power oscillations and increases the transient stability
•Increase power transmission capability
•Decrease power transmission losses
•Improved load sharing capability

5. Static VAR Compensator
•SVCs are shunt devices that can control line voltages.
•The SVC is a parallel combination of many fixed or switched branches,
of which atleast one has thyristors, and combination of branches
depend on requirements.
•It generates reactive power by switching capacitor banks when
system voltage is low or loads are inductive.
•Likewise, the SVC absorbs reactive power when system voltage is high
or loads are capacitive.

6. Design and Configuration
There are three common configurations of SVCs,

1.Thyristor-controlled Reactors with Fixed Capacitors (TCR/FC)
2.Thristor switched capacitors (TSC)
3.Thyristor-controlled Reactors and Thyristor switched capacitors
(TCR/TSC)

7. Thyristor-controlled Reactors with Fixed
Capacitors (TCR/FC)

•This SVC design consists of two parallel branches connected on the
secondary side of a coupling transformer. One of the branches is
composed of reactors that are controlled by AC thyristor switches.
•In addition, the reactors are connected in delta for three-phase
applications. The other branch could either be fixed capacitor banks
or shunt filters.
•The variation of reactive power is accomplished by controlling the
thyristor’s firing instants and, accordingly, the current that flows by
the reactance.

8. TCR with FC

9. SVC V-I Characteristic





The SVC can be operated in two different modes:
•In voltage regulation mode (the voltage is regulated within limits)
•In var control mode (the SVC susceptance is kept constant)
When the SVC is operated in voltage regulation mode, it implements
the following V-I characteristic.

10. SVC v-i characteristic

11. •As long as the SVC susceptance (B) stays within the maximum and minimum
susceptance values imposed by the total reactive power of capacitor
banks (Bc
max
) and reactor banks (Bl
max
), the voltage is regulated at the reference
voltage V
ref
.
•However, a voltage drop is normally used (usually between 1% and 4% at maximum
reactive power output), and the V-I characteristic has the slope indicated.
The V-I characteristic is described by the following three equations:








SVC v-i characteristic

12. Where,
V denotes the positive sequence voltage
I denotes the reactive current (I>0 indicates an inductive current)
X
s
denotes the slope or droop reactance
Bc
max
denotes the maximum capacitive susceptance with all TSCs
in service, no TSR or TCR
Bl
ma
denotes the maximum inductive susceptance with all TSRs
in service, or TCRs at full conduction, without TSC.
SVC v-i characteristic

13. Benefits of SVCs

• Maximized power compensation
• Near-instantaneous response to system voltage variations
• Increased customer’s economic benefits
• Eliminate harmonics and reduce voltage distortion with
appropriate shunt filters
• Load balancing on three-phase systems

14. Thyristor Controlled Series Capacitor
•TCSC is a series FACTS device and is a capacitive reactance
compensator.
•In this TCSC theory the capacitor is inserted directly in series with the
transmission line and the thyristor controlled inductor is mounted
directly in parallel

15. Uses of TCSC
•Increases power transmission capability
•Improve system stability
•Reduce system losses
•Improve voltage profile of the lines
•Optimize power flow between parallel lines
•Damping of the power swings from local and inter area oscillations

16. Operating modes of TCSC
•Blocking mode
•Bypass mode
•Capacitive boost mode
•Inductive boost mode

17. Modes of TCSC

18. Operation
•In case of blocked operating mode, the thyristor valve is not triggered
and the thyristor are kept in non-conducting state.
•In case of bypass mode, as the thyristors are fully conducting, most of
the line current flows through thyristors and hence TCSC has small net
inductive reactance.
•In vernier control, thyristors are conducted in such a manner that a
controlled amount of inductive current can circulate through the
capacitor, thereby increasing effective capacitance/inductive
reactance of the module.

19. Drawbacks of FACTS devices


•Major disadvantage is that these devices are non linear devices
•They induce harmonics in the output signal of the system
•Cost is high

20. Thank you