Download Academic paper: Implementation of Shunt and Series FACTS

International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
Implementation of Shunt and Series
FACTS Devices for Overhead
Transmission Lines
C.Dinakaran, Assistant Professor, Dept. of EEE, Sri Venkateswara College of Engg. & Tech., Chittoor
[email protected]
Abstract — In this paper proposes optimal location and
parameters of Unified Power Flow Controllers (UPFCs) to unify
the power flow in electrical power systems. Shunt and Series
FACTS devices are used for controlling the transmission
voltage, power flow and reducing reactive losses and damping of
power system oscillations for high power transfer levels. FACTS
devices are very efficient and increasing the power transfer
capability of a line, With the improvements in current and
voltage handling capabilities of the power electronic devices that
have allowed for the development of Flexible AC Transmission
System (FACTS), the possibility has arisen in using different
types of controllers for efficient shunt and series compensation.
In series compensation, the FACTS devices are connected in
series with the power system. It works as a controllable voltage
source. Shunt compensation power system is connected in shunt
with FACTS. It works as a controllable current source. The
shunt FACTS device is operated at that rating that is able to
control the bus voltage of shunt FACTS device equal to sending
end voltage so as to get the maximum possible benefit of
maximum power transfer and stability under steady state
conditions. The performance of optimal location of shunt and
series FACTS devices are verified by simulation using
MATLAB/SIMULINK and Power World Simulator.
Key Words — Shunt Compensation, Series Compensation,
STATCOM, Optimal Location, Power Converter, UPFC.
I. INTRODUCTION
FACTS devices can be connected to a transmission
line in various ways, such as series and shunt devices towards
maintain voltage stability in transmission lines. Thyristor
controlled phase shifting transformer (TCPST) and unified
power flow controller (UPFC) connections are series and
shunt combination [1], [5]. In series compensation, the
FACTS are connected in series with the power system, it
works as a controllable voltage source. Series inductance
occurs in long transmission lines and when a large current
flow causes a large voltage drop [2] - [3]. To compensate,
series capacitors are connected. In shunt compensation,
power system is connected in shunt with the FACTS. It works
as a controllable current source. The pressure associated with
economical and environmental constraints has forced the
power utilities to meet the future demand by fully utilizing the
existing resources of transmission facilities without building
new lines. FACTS devices are very effective and capable of
increasing the power transfer capability of a line, as thermal
limits permit, while maintaining the same degree of stability
[4]. Numerous recent applications of FACTS have proven to
be cost-effective, long-term solutions. With the improvements
in current and voltage handling capabilities of the power
electronic devices that have allowed for the development of
Flexible AC Transmission System (FACTS), the possibility
has arisen in using different types of controllers for efficient
shunt and series compensation [6].
Applying FACTS on a broad-scale basis for both
series and Shunt FACTS devices are used for calculating
transmission voltage, power flow, reducing reactive losses
and damping of power system oscillations for high power
transfer levels [7]. The extensive active considerations of the
equipment of FACTS controllers for improved
controllability. Shunt capacitive compensation is used to
develop the power factor. When an inductive load is coupled
to the transmission line, power factor lags for the reason that
of lagging load current. To compensate a shunt capacitor is
connected which draws current foremost the source voltage
[8] – [9].
Shunt inductive compensation is used moreover
when charging the transmission line, when there is extremely
low load at the receiving end. Due to no load, very low current
flows from beginning to end the transmission line. Shunt
capacitance in the transmission line effects voltage
amplification. To balance a no-loss line, voltage magnitude at
receiving end is the same as voltage magnitude at sending end
(VS = VR=V). Transmission results in a phase lag ‘δ’ that
depends on line reactance ‘X’. Shunt inductors are linked
across the transmission lines [10].
The FACTS is a standard term instead of the
application of power electronics based solutions to AC power
system. These systems can offer compensation in series or
shunt or a grouping of both series and shunt [11]-[12]. The
FACTS can effort the compensation by modifying
impedance, voltage or phase angle [13].
2009
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
bi-directional compensation to the line by injecting
compensating voltage into the series line.
Therefore, SSSC is often used to enhance the
dynamic behavior of power system by providing temporarily
increment and decrement of real power into the line as
compensation.
Fig. 2 Schematic Diagram of SSSC
Fig. 1 Transmission on a no-loss line and Phasor diagram
The ability of FACTS in provided that series or
shunt compensation is explained with the help of transmission
line [14]. In the case of a no-loss transmission line, voltage
magnitude at receiving end is the identical as voltage
magnitude at sending end (V1 = V2= V). Fig.1 shows
equivalent circuit and Phasor diagram of no loss transmission
line.
B. THYRISTOR CONTROLLED SERIES
COMPENSATOR (TCSC)
Thyristor controlled series compensator consists of a
series capacitor bank shunted by a thyristor-controlled reactor
in order to provide a smoothly variable series capacitive
reactance as shown in Fig.3. The bi-directional thyristor valve
that is fired with an angle ‘α’ ranging between 90° and 180°
with respect to the capacitor voltage.
II. SERIES COMPENSATION
The series Compensator could be variable impedance
such as capacitor and reactor are Power Electronics based
variable source of main frequency to serve the desired need.
Various Series connected FACTS devices are,
Static Synchronous Series Compensator
Thyristor Controlled Series Capacitor
Thyristor Switched Series Capacitor
Thyristor Controlled Series Reactor
Thyristor Switched Series Reactor
A. STATIC SYNCHRONOUS SERIES COMENSATOR
(SSSC)
Fig. 3 Schematic Diagram of TCSC
Static series compensator (SSSC) is generally
implemented using GTO based voltage source inverter that
can provide controllable compensating voltage over an
identical capacitive or inductive range independent of the line
current as shown in Fig.2. The basic operation of SSSC is
very much analogous to the conventional series
compensation, except that it uses switching power converter
as a synchronous voltage. SSSC is able to provide
The TCSC can be operated in bypass thyristor mode,
blocked thyristor mode and vernier mode. In bypass thyristor
mode, the thyristors are made to fully conduct with a
conduction angle of 1800. Gate pulses are applied as soon as
the voltage across the thyristors reaches zero and becomes
positive, resulting in a continuous flow of current through the
thyristor valves. The TCSC module behaves like a parallel
capacitor inductor combination.
2010
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
In blocked thyristor mode, the firing pulses to the
thyristor valves are blocked. If the thyristors are conducting
and a blocking command is given. The thyristors turn off as
soon as the current through them reaches a zero crossing. The
net TCSC reactance is capacitive.
The vernier mode allows the TCSC to behave either
as a continuously controllable capacitive reactance or as a
continuously controllable inductive reactance. It is achieved
by varying the thyristor pair firing angle in an appropriate
range.
C. 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. It consists of a capacitor shunted by a pair of
reversely parallel connected thyristor. The basic component
that makes up a thyristor switched series capacitor is shown in
Fig.4. The operation of TSSC is to make use of a thyristor to
act as a valve or switch for the capacitor connected parallel to
it such that when thyristor is triggered the capacitor will be
activated to start compensation.
When the firing angle of the thyristor controlled
reactor is 1800, it stops conducting and the uncontrolled
reactor acts as a fault current limiter. As the angle decreases
below 1800, the net inductance decreases until firing angle of
900, when the net inductance is the parallel combination of the
two reactors. The TCSR may be a single large unit or several
smaller series units.
E. THYRISTOR SWITCHED SERIES REACTOR
(TSSR)
An inductive reactance compensator which consists
of a series reactor shunted by a thyristor-switched reactor in
order to provide a stepwise control of series inductive
reactance. TSSR is 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. This is complement of TCSR, but
with thyristor switches fully ON or fully OFF to achieve a
combination of stepped series inductance.
III. SHUNT COMPENSATION
Shunt Controllers may be variable impedance,
variable source or a combination of these two. In principle, all
shunt Controllers inject current into the system at the point of
connection. Various shunt connected controllers are,
Static Compensator
Static VAR Compensator
Thyristor Controlled Reactor
Thyristor Switched Capacitor
A. STATIC COMENSATOR (STATCOM)
Fig. 4 Schematic Diagram of TSSC
D. THYRISTOR CONTROLLED SERIES REACTOR
(TCSR)
TCSR is an inductive reactance compensator
consists of a series reactor shunted by a thyristor controlled
reactor in order to provide a smoothly variable series
inductive reactance as shown in Fig.5.
Fig. 5 Schematic Diagram of TCSR
Fig. 6 Schematic Diagram of STATCOM
2011
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
STATCOM is a self commutated switching power
converter supplied from an appropriate electric energy source
and operated to produce a set adjustable multiphase voltage,
which may be coupled to an AC power system for the purpose
of exchanging independently controllable real and reactive
power. The STATCOM is a solid-state based power converter
version of the SVC. Operating as a shunt connected SVC, its
capacitive or inductive output currents can be controlled
independently from its terminal AC bus voltage.
Basically, STATCOM is comprised of three main
parts as shown in Fig.6. A Voltage source converter (VSC) is
a step-up coupling transformer and a controller. The
advantages of STATCOM compared to other shunt
compensators are equality of lagging and leading output,
continuous reactive power control with fast response and
possible active harmonic filter capability.
SVC, in which conduction time and hence, current in a shunt
reactor is controlled by a thyristor based AC switch with firing
angle control. The TCR consists of a fixed reactor of inductor
L and a bi-directional Thyristor valve.
D. THYRISTOR SWITCHED CAPACITOR (TSC)
TSC is 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. The TSC is different from TSR and TCR as its branch
can be switched out at zero crossing of the current, as shown
in Fig.8.
B. STATIC VAR COMPENSATOR (SVC)
SVC is “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”.
Fig. 8 Representation of FACTS for shunt compensation
IV. OPTIMAL PLACEMENT OF STATIC VAR
COMPENSATOR (SVC)
Fig. 7 Schematic Diagram of Static VAR Compensator
Basically an SVC consists of a combination of fixed
capacitors or reactors, Thyristor Switched Capacitors (TSC)
and Thyristor Controlled Reactors (TCR) connected in
parallel with the electrical system as shown in Fig.7. The basic
structures and idea of the TSC is to split up a capacitor bank
into sufficiently small capacitor steps and switch these steps
on and off individually, using anti-parallel connected
Thyristors as switching elements.
C. 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. TCR is a
shunt connected, thyristor controlled inductor whose effective
reactance is varied in a continuous manner by partial
conduction control of the thyristor valve. TCR is a subset of
The electric power industry in the present is very
complex and undergoes unforeseen rapid changes in terms of
demand/generation patterns and trading activities that hinder
the system security. Load curtailment is the collection of
control strategies employed to reduce the electric power
loading in the system and main aim is to push the disturbed
system towards a new equilibrium state. Load curtailment
may be required even when voltages at some buses deviate
from their acceptable voltage limits. In such cases, reactive
power is supplied locally to keep the voltages within limits.
The main disadvantage of the reactive power over the active
power is that it cannot be transmitted over long distances and
hence must be provided locally by some means.
Flexible AC Transmission Systems (FACTS)
controllers can be a suitable alternative to provide such
reactive power locally. Generators have the capability of
controlling reactive power but the location of the reactive
power demand can hinder their effects considerably. Due to
high costs of FACTS devices, their proper location in the
system must be ascertained. In the impacts of TCSC and SVC
on system load curtailments based on optimal power flow
(OPF) are studied by placing the devices in the system on a hit
and trial basis.
2012
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
V. SYSTEM MODELING
The modeling of a transmission line and the static
representation of Static VAR Compensator (SVC) has been
described in this part.
A. REPRESENTAION OF TRANSMISSION LINE
A simple transmission line connected between bus-i
and bus-j can be represented by its lumped π equivalent
parameters as shown in Fig.9. The complex voltages at bus-i
and bus-j have been represented by Vi∠ δi and Vj∠ δj
respectively. The real (Pij) and reactive (Qij) powers from
bus-i to bus-j can be written as,
Pij = Vi2gij – ViVj(gijcosδij + bijsinδij)
Qij = - Vi2(bij+Bsh/2) – ViVj(gijsinδij – bijcosδij)
Is are related to the receiving end voltage Vr and current Ir
through ABCD constants as,
Vs = AVr + BIr
(5)
Is = CVr + DIr
(6)
VI. EXPERIMENTAL RESLTS
A. SIMULATION RESULT
The proposed method has been tested and simulation
results are shown in Fig.11. This model has been implemented
using MATLAB/SIMULINK environment with SIMPOWER
system toolbox.
(1)
(2)
Similarly, the real (Pji) and reactive (Qji) from bus-j to bus-i
can be written as,
Pji = Vj2gij – ViVj(gijcosδij – bijsinδij)
(3)
Qji = - Vj2(bij+Bsh/2) + ViVj(gijsinδij + bijcosδij)
(4)
Fig. 9 Static Representation of Transmission Line
B. TRANSMISSION LINE MODEL
The transmission line parameters are uniformly
distributed and the line can be modeled by a 2-port, 4-terminal
network as shown in Fig.10 represents the actual line model.
The relationship between sending end (SE) and receiving end
(RE) quantities of the line are represented in equations 5 & 6.
Fig. 10 Representation of 2 – Port, 4 – Port Terminal network of a
Transmission Line
Transmission lines are operated with a balanced three
phase load, the analysis can proceed on a per phase basis. A
transmission line on a per phase basis can be regarded as a two
port network, whereas the sending end voltage Vs and current
Fig. 11 Simulation Circuit of Three Phase Shunt and Series Compensated
Network
2013
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
Fig. 14 Voltage and Current Waveforms for Signal B 3
Fig. 12 Voltage and Current Waveforms for Signal B1
B. OPTIMAL LOCATION OF SHUNT AND
SERIES FACTS DEVICES
Fig. 13 Voltage and Current Waveforms for Signal B2
2014
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
C. POWER WORLD SIMULATOR
Power World Simulator is an interactive power
system simulation package designed to simulate high voltage
power system operation on a time frame ranging from several
minutes to several days. Power world Simulator is used to
carry out the simulations and represent the results graphically.
2015
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines
International Electrical Engineering Journal (IEEJ)
Vol. 6 (2015) No.8, pp. 2009-2017
ISSN 2078-2365
http://www.ieejournal.com/
VII. CONCLUSION
Modern Power Systems are designed to operate
efficiently to supply power on demand to various load centres
with high Reliability. The effects of shunt and series
compensation on the best location of a shunt and series
FACTS device to obtain the utmost possible advantage of
maximum power transfer as well as system stability.
Generally power systems networks are large and complex.
Now-a-days, increase the loads connected to the system and
more demands transfer of huge power to the transmission
lines. The variation in the optimal location of the shunt
FACTS device from the centre point of line depends upon the
extent of series compensation and it increases approximately
linear from the centre point of the transmission line towards
the generator side as the extent of series compensation is
increased. Mutually the power transfer capacity and strength
of the system can be enhanced much more if the shunt and
series FACTS devices are located at the new optimal location
in its place of the mid-point of the line. The result of series and
shunt compensations controllers in attractive power system
stability has been examined.
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Control Strategy between NTDC and KESC Interconnection Using
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[13] J.Vivekananthan, R.Karthick, “Voltage Stability Improvement and
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2016
C.Dinakaran
Implementation of Shunt and Series FACTS Devices for Overhead Transmission Lines