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EE 551
POWER SYSTEMS COMPONENTS
UNIT 1 – TRANSMISSION LINES
(FACTS Devices and Their
Applications in Power System)
Dr. E. K. ANTO
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1.6: FACTS Devices Introduction
 Due to modernization, heavy industrialization, economic
growth, etc., power demand has witnessed a
substantial increase
 However, there has been no corresponding expansion
of the transmission lines, because of limited resources,
difficulty in the acquisition of ROWs and environmental
concerns.
 Consequently, transmission lines are heavily loaded,
 And so power transfer, as well as system stability, are
getting affected.
 As a solution, Flexible AC transmission systems (FACTS)
devices have been introduced to solve various power
system steady-state control problems, enhance
controllability and increase power transfer capability.
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1.6: FACTS Devices –
Introduction (2)
 Recall the known active and reactive power flow
equations for a “lossless” transmission line:

;


 Power flows (real and reactive) are functions of three
parameters, namely, (i) voltage, (ii) phase angle
difference and (iii) reactance of the transmission lines.
 Accordingly, real and reactive power can be controlled
by controlling the phase angle difference (power
angle), voltage magnitude, as well as the reactance of
the line through series compensation.
 Generally, FACTS devices allow the dynamic control of
power systems
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1.6: FACTS Devices Introduction (3)
 Let us look at “how” these power system variables
can be controlled.
 Generally, two (2) main devices can be employed
for controlling those power system parameters
 These are:
 Conventional equipment – usually for static controls;
less expensive, but limited in dynamic behaviour
 FACTS devices – usually for dynamic controls; 1st
generation types use SCRs for control; 2nd generation
types use GTOs and IGBTs for control
 Through the controls, the performance of the
power system is enhanced
1.6.1: Conventional Equipment 5
for static controls
SN
Conventional equipment
Parameter controlled
1
Series capacitor
Reactance (hence active
power flow)
2
Shunt capacitor and reactor
Voltage
3
Transformer LTC (online tap changer) Voltage
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Phase shifting transformer
Angle
5
Synchronous condenser
Voltage
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Others (reconductoring, addition of
new lines, etc.)
Reactance and voltage
1.6.2: FACTS Devices -
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for dynamic controls
SN
FACTS device
Parameter controlled
1
Static VAR Compensator (SVC) – 1st
generation
Voltage
2
Thyristor Controlled Series Compensator Reactance (and hence
(TCSC)-1st generation
active power flow)
3
Thyristor Controlled Phase Shifter (TCPS)
– 1st generation
Angle
4
Static Synchronous Compensator
(STATCOM) – 2nd generation
Voltage
5
Static Synchronous Series Controller
(SSSC) – 2nd generation
Reactance
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Unified Power Flow Controller (UPFC) –
2nd generation
Reactance
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Convertible Series Compensator (CSC)
Reactance
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Interphase Power Flow Controller (IPFC)
Angle
1.6.3: Benefits of FACTS Devices
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in transmission system
 (1) Control of power flow;
 (2) Increased power transfer capability of a line;
 (3) Increased loadability of the system;
 (4) Voltage control/improved voltage stability;
 (5) Reactive power (load) compensation;
 (6) Power quality improvement;
 (7) Mitigation of flickers.
 (8) Mitigation of sub-synchronous reactance (SSR);
 (9) Enhanced system dampening of oscillations;
 (10) Improved transient stability limit of system;
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THE END