FACTS.pdf

Naran Pindoriya, IITGN
FLEXIBLE AC TRANSMISSION
SYSTEMS (FACTS)

Major Topics
• Objectives of FACTS controllers;
• Shunt controllers - Static VAR Compensator (SVC) and
Static Synchronous Compensator (STATCOM);
• Series controllers - Thyristor Controlled Series
Capacitor (TCSC), Thyristor Controlled Phase Angle
Regulator (TCPAR), and Static Synchronous Series
Capacitor (SSSC); Combined shunt and series
controllers - Unified Power Flow Controller (UPFC);
Applications of FACTS controllers - stability improvement
and congestion management in power system.

Textbooks & References
 Hingorani N.G. and Gyugyi L., Understanding FACTS: Concepts
and Technology of Flexible AC Transmission Systems, IEEE
Press, Standard Publishers Distributors, 1st Indian Edition,
2001.
 R. M. Mathur and R. K. Varma, “Thyristor-based FACTS
Controllers for Electrical Transmission Systems, IEEE Press,
Wiley, 2002
 Padiyar, K.R., FACTS Controllers in Power Transmission and
Distribution, New Age International, 1st Edition, 2007

FACTS
 AC Transmission system incorporating power
electronics and/or static controllers, to enhance the
controllability and the power transfer capability
 FACTS Controller: A power electronic-based system
and other static equipment that provide control of
one or more AC transmission system parameters

FACTS
 FACTS mainly find applications in the following areas:
– Power transmission
– Power quality
– Railway grid connection
– RES Integration
– Cable systems
 With FACTS, the following benefits can be attained in
AC systems:
– Improved power transmission capability
– Improved system stability and availability
– Improved power quality
– Minimized environmental impact
– Minimized transmission losses

FACTS
 FACTS are a family of devices which can be inserted
into power grids in series, in shunt, and in some
cases, both in shunt and series
 Important applications in power transmission and
distribution involve devices such as
– SVC (Static Var Compensators),
– Fixed Series Capacitors (SC)
– Thyristor-Controlled Series Capacitors (TCSC)
– and STATCOM

Lossless Distributed Line Parameter
 
  x
Z
V
j
x
I
x
I
x
I
jZ
x
V
x
V
R
R
R
R




sin
cos
sin
cos
0
0




For a loss less line, the general solutions:


c
l
Z0
length
Electrical
rad
a
c
l
a
km
rad
c
l






 /
a
jZ
a
V
V
I
R
S
R


sin
cos
0


 


 sin
cos
0
j
V
V
V
V
V
Let
S
S
S
R
R








 
a
Z
a
V
V
V
j
a
Z
V
V
I
V
jQ
P
S
R
R
S
R
S
R
R
R
R
R





sin
cos
cos
sin
sin
0
2
0
*






 
a
Z
V
V
a
V
j
a
Z
V
V
I
V
jQ
P
S
R
S
S
R
S
S
S
S
S
S





sin
cos
cos
sin
sin
0
2
0
*






line
the
in
generation
absorption
power
reactive
of
because
Q
Q
line
lossless
for
ected
as
P
P
R
S
R
S
/
,
exp
,



 For short line
X
la
l
Z
l
Z
l
l 



 



 0
0 sin
sin 
sin
X
V
V
P R
S

 Symmetrical lines, V
V
V R
S 



sin
sin
0
2
a
Z
V
P 
0
2
0
Z
V
P
SIL 
 
a
P
P


sin
sin
0

 Mid point condition of a symmetrical line
2
sin
2
cos 0
a
I
jZ
a
V
V m
m
S




m
m
m
m
R
S
m
m
V
P
I
Q
and
P
P
P
P
V
V
Let







0
0
2
sin
2
cos 0
a
V
P
jZ
a
V
V
m
m
S




0
0
2
P
Z
V
and
V
V
Setting norm
norm
S 

2
/
1
2
2
0
4
2 2
tan
2
cos
4
1
2
cos
2
1
~





















a
P
P
a
a
Vm




a
P
P


sin
sin
0

0.588
1.1058
The typical
voltage
distribution on
a distributed
line

Mid-Point Compensation


S
V 0

R
V
2


m
V
m
Q m
Q
m
c Q
Q 2

Fixed Reactor or Continuous
VAR Controller
2
sin
2
cos
2
cos
0
2
a
Z
V
V
a
V
Q
m
S
S
m











2
sin
2
sin
0
a
Z
V
V
P
m
S
comp



Mid-point over voltage control: Vm=1 pu
VAr compensator absorb
reactive power, if P<P0,
otherwise, if P>P0, it supplies.

VAr Control
 Passive VAr control: When fixed inductors and/ or
capacitors are employed to absorb or generate
reactive power, they constitute passive control.
 Active VAr control: Active VAr control is produced
when its reactive power is changed irrespective of
the terminal voltage to which the VAr controller is
connected.
External devices or subsystems that control the performance of
the transmission lines are known as compensators.
• to increase the power-transmission capacity of the line, and/ or
• to keep the voltage profile of the line along its length within
acceptable bounds to ensure the quality of supply to the
connected customers as well as to minimize the line-insulation
costs.
Objectives

Passive Reactive Power Compensation
 Transmission line has series inductance which absorb reactive
power while the shunt capacitance generates the reactive
power.
 For light load --- the absorption is less than the generation
and voltage in the line tends to raise.
 At the load exceeding the SIL --- the absorption is higher
than the generation and voltage in the line tends to fall.
 By connecting series capacitors and shunt inductors in the
line, we can control the reactive power flow in the line to limit
the voltage variation and increase active power transfer
capability.
)
.
(
1 line
Symm
pu
V
V
V R
S 



 Distributed Compensation
Difficult to arrange, but is easier to analyze
o Distributed series compensation (capacitive) whose effect, in steady
state, is to counterpart the effect of distributed series inductance of the
line.
o Distributed shunt compensation (Inductive), the effect of line
capacitance is reduced.
The phase constant (’) of a compensated line is given by
      
1
deg
1
deg
tan
1
1
1
1
'
'
'












on
compensati
shunt
of
ree
k
on
compensati
series
of
ree
k
line
ted
uncompensa
of
t
cons
phase
k
k
k
c
k
l
c
l
sh
se
sh
se
sh
se








The surge impedance (Zs’) of a compensated line is given by
 
 
line
ted
uncompensa
of
impedence
surge
Z
k
k
Z
c
l
Z
s
sh
se
s
s





1
1
'
'
'

 Zs is reduced by series
compensation (capacitive)
and increased by shunt
compensation (inductive)
The electrical length (’l ) of a compensated line is given by
  
sh
se k
k
l
l 

 1
1
' 

Electrical length is reduced
by both series compensation
(capacitive) and shunt
compensation (inductive)

 Power flow in a symmetrical lossless line
 






sin
1
sin
'
'
sin
'
sin
'
'
2
2
2
se
s
s
s k
l
Z
V
l
Z
V
l
Z
V
P




2
sin
2
cos 0
a
I
jZ
a
V
V m
m
S




2
'
cos
'
l
V
V m


 No-load mid point voltage
2
sin
2
cos
2
cos
0
2
a
Z
V
V
a
V
Q
m
S
S
m











 No-load mid point reactive power
 
sh
s
s
s
m k
Z
l
V
l
Z
V
l
Z
V
Q 


 1
2
2
'
'
2
'
tan
'
'
2
2
2




 The distributed shunt compensation reduces the no-
load voltage and charging reactive power, but has
little effect on maximum power flow in the line.
 The distributed series compensation reduces the no-
load voltage and increase the power transfer
capacity, but has little effect on no load charging
reactive power.

Mid-point compensation
S
I
S
V R
V
R
I
l
Z
Z s 
sin
'
2
tan
1
2
' l
Z
Y
s


2
tan
1
2
' l
Z
Y
s


Π - Model of long transmission line (uncompensated)
c
jX

4
tan
l
jZs

4
tan
l
jZs

Series capacitor and
shunt reactor connected
at the midpoint

Mid-point compensation
 Series compensation accompanied by shunt compensation
S
I


S
V 0

R
V
R
I
2
sinh
l
Zs

c
jX

2
sinh
l
Zs



























































2
sin
2
1
2
cos
2
sin
2
1
sin
2
cos
sin
sin
2
sin
2
l
Z
X
l
P
l
Z
X
l
Z
l
V
V
P
X
l
Z
V
V
P
s
c
uncomp
s
c
s
R
S
comp
c
s
R
S
comp









Shunt Passive Compensation
 Shunt reactor
– Compensate for the line capacitance,
and it controls overvoltage at no-load
and light load
 Shunt capacitor
– to increase the power-transfer
capacity and to compensate for the
reactive-voltage drop in the line
– creates higher-frequency–resonant
circuits and can therefore lead to
harmonic overvoltage on some
system buses

Series Passive Compensation
 Series capacitors are used to partially offset the effects
of the series inductances of lines
 Series compensation results in the improvement of the
maximum power-transmission capacity of the line
 reactive-power absorption of a line depends on the
transmission current, so when series capacitors are
employed, automatically the resulting reactive-power
compensation is adjusted proportionately.
 Also, because the series compensation effectively
reduces the overall line reactance, it is expected that the
net line-voltage drop would become less susceptible to
the loading conditions.

Thyristors controlled reactor current

Major FACTS Devices: Overview

Basic Types of FACTS Controllers
IPFC
UPFC

 Thyristor Switched Reactor (TSR): A shunt-connected,
thyristor-switched inductor whose effective reactance is
varied in a stepwise manner by full- or zero-conduction
operation of the thyristor valve.
 Thyristor Controlled Reactor (TCR): A shunt-connected,
thyristor-controlled inductor whose effective reactance is
varied in a continuous manner by partial-conduction control of
the thyristor valve.
 Thyristor Switched Capacitor (TSC): A shunt-connected,
thyristor-switched capacitor whose effective reactance is
varied in a stepwise manner by full- or zero-conduction
operation of the thyristor valve.
Shunt Connected Controllers

 Static VAr Compensator (SVC): A shunt-connected static VAr
generator or absorber whose output is adjusted to exchange
capacitive or inductive current so as to maintain or control
specific parameters of the electrical power system (typically
bus voltage).
Some other control features are:
• voltage control
• reactive power control
• damping of power oscillations
• unbalance control

 Static Synchronous Compensator (STATCOM): A Static
synchronous generator operated as a shunt-connected static VAr
compensator whose capacitive or inductive output current can be
controlled independent of the ac system voltage.
STATCOM
Source: TMT&D Corporation, Japan

Objectives of Shunt Compensation (1/3)
29
EE 308 HVDC and FACTS
 Improves the voltage stability
For a radial line
with fixed VS







 


R
R
R
S
R
S
V
jQ
P
l
jZ
l
V
V 
 cos
cos
Quadratic equation
can be solved for VR
Natural load
Shunt reactive
compensation can
effectively increase
the voltage stability
limit by supplying
the reactive load

Objectives of Shunt Compensation (2/3)
 Improvement of Transient stability
Without compensation
(base case)
With ideal mid point compensation
2
sin
2
sin
0
a
Z
V
V
P
m
S
comp




 Power oscillation damping
VAr output of the shunt compensator
Generator angle
Transmitted power

SVC Configurations
TCR-FC-Filter : Single line diagram
• FC-TCR
• TSC-TCR

Analysis of SVC: TCR
  t
V
t
vs 
sin

Single-Phase TCR
• The controllable range of the TCR firing angle, , extends from 90°
to 180°.
• A firing angle of 90° results in full thyristor conduction with a
continuous sinusoidal current flow in the TCR.
• As the firing angle is varied from 90° to close to 180°, the current
flows in the form of discontinuous pulses symmetrically located in
the positive and negative half-cycles.

  














2
sin
2
2
1
L
V
I
where  is the firing angle measured from positive going zero crossing of the applied
voltage.
Fourier analysis is used to derive the fundamental component of the TCR current )
(
1 
I
Solving,

      L
B
B
B
where
VB
I TCR
TCR 






 /
1
,
2
sin
1
2
2
, max
max
1 












180
90
,
,
2




 



 angle
conduction
where
   




 TCR
B
V
B
V
I 





 

sin
max
1
• TCR acts as variable susceptance.
• Variation of the firing angle changes the
susceptance and consequently, the
fundamental current components,
which leads to a variation of reactive
power absorbed by the reactor because
the applied ac voltage is constant.

Fundamental Current
  














2
sin
2
2
1
L
V
I

Harmonics: TCR
   
  ...
3
,
2
,
1
,
1
2
;
1
sin
cos
cos
sin
4
2











 k
k
n
n
n
n
n
n
L
V
In







Operating Characteristics
Operating V-I area of TCR
max
TCR
I
max
TCR
V
SVC
SVC
SVC B
V
j
I  TCR
SVC B
B 

FC-TCR SVC
SVC
SVC
SVC B
V
j
I 
TCR
C
SVC B
B
B 


FC-TCR SVC
Without step-down transformer

FC-TCR SVC
With step-down transformer
90°

STATCOM
X
E
V
I


2
1
V
X
V
E
Q


)
(
;
)
(
;
inductive
Q
absorbs
converter
V
E
capacitive
Q
generates
converter
V
E
if



STATCOM

STATCOM+FC

STATCOM+FR

STATCOM+TCR+TSC

SVC Vs. STATCOM
V-I
Characteristics
V-Q
Characteristics

SVC Vs. STATCOM
STATCOM SVC
able to control its output current over
the rated maximum capacitive or
inductive range independently of AC
system voltage
the maximum attainable compensating
current of the SVC decreases linearly
with AC voltage
maintain full capacitive output current
at low system voltage makes it more
effective in improving the transient
stability
comparatively less capability for
improving transient stability
provide bit active power compensation does not have capability of providing
any active power compensation
Fast response Comparatively slow
STATCOM is more effective than the SVC in providing voltage support
under large system disturbances during which the voltage excursions
would be well outside of the linear operating range of the compensator

 Thyristor-Switched Series Reactor (TSSR): An inductive
reactance compensator which consists of a series reactor
shunted by a thyristor-controlled switched reactor in order to
provide a stepwise control of series inductive reactance.
 Thyristor-Controlled Series Reactor (TCSR): An inductive
reactance compensator which consists of a series reactor
shunted by a thyristor controlled reactor in order to provide a
smoothly variable series inductive reactance.
 Thyristor-Switched Series Capacitor (TSSC): A capacitive
reactance compensator which consists of a series capacitor
bank shunted by a thyristor-switched reactor to provide a
stepwise control of series capacitive reactance.
 Thyristor Controlled Series Capacitor (TCSC): A capacitive
reactance compensator which consists of a series capacitor
bank shunted by a thyristor-controlled reactor in order to
provide a smoothly variable series capacitive reactance.
Series Connected Controllers

Power Flow control

sin
C
L
R
S
X
X
V
V
P



Series Compensation
Voltage Stability

Series Compensation
Improvement in Transient Stability
Base case With compensation

Damping of power oscillations

TSSC or TCSC
TSSR or TCSR
Practical TCSC module
Metal-oxide varistor (MOV), essentially a nonlinear resistor -
prevent the occurrence of high-capacitor over-voltage
If the TCSC valves are required to operate in the fully “on”
mode for prolonged durations, the conduction losses are
minimized by installing an ultra–high-speed contact (UHSC)
across the valve.

Series Connected Controller: TCSC

An actual TCSC system usually comprises a cascaded combination of
many such TCSC modules, together with a fixed-series capacitor, CF .
This fixed series capacitor is provided primarily to minimize costs.

TCSC Installation in India
PGCIL, Raipur, TCSC Project on 400 kV Raipur- Rourkela Double Circuit
Lines (412 km)
Power Grid Corporation of India Ltd (PGCIL) has purchased two Thyristor
Controlled Series Capacitors (TCSC) from ABB.

TCSC Installation in India
Source:
ABB

 
  C
L
C
L
eff
X
X
X
X
j
X





  













2
sin
2
L
L X
X
  

 
L
L X
X
Series FACTS Controller: TCSC

 Static Synchronous Series Compensator (SSSC): A
static synchronous generator operated without an
external electric energy source as a series
compensator whose output voltage is in quadrature
with, and controllable independently of, the line
current for the purpose of increasing or decreasing
the overall reactive voltage drop across the line and
thereby controlling the transmitted electric power.
Series FACTS Controller: SSSC

SSSC
• Voltage-sourced converter-based series compensator - Static
Synchronous Series Compensator (SSSC)
• Proposed by Gyugyi, 1989
Basic concept :
the same steady-state power transmission can be established if the
series compensation is provided by a synchronous ac voltage source

SSSC
jkXI
I
jX
V
V c
C
q 




maintain a constant compensating voltage in the presence of
variable line current, or control the amplitude of the injected
compensating voltage independent of the amplitude of the line
current
 
I
I
jV
V q
q 



SSSC
  2
sin
cos
1
2
cos
sin
*
*




L
q
s
L
r
s
L
q
s
L
r
s
L
r
q
s
s
s
X
V
V
X
V
V
Q
X
V
V
X
V
V
P
I
jX
V
V
V
V
I
V
S












 




 Thyristor-Controlled Phase Angle Regulator (TCPAR):
A phase-shifting transformer adjusted by thyristor
switches to provide a rapidly variable phase angle.
Combined Shunt and series Connected Controllers

Unified Power Flow Controller (UPFC): A combination of static
synchronous compensator (STATCOM) and a static series
compensator (SSSC) which are coupled via a common de link, to
allow bidirectional flow of real power between the series output
terminals of the SSSC and the shunt output terminals of the
STATCOM, and are controlled to provide concurrent real and
reactive series line compensation without an external electric
energy source.
Combined Shunt and series Connected Controllers

FACTS.pdf

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FACTS.pdf