This paper provides a review of FACTS devices. The value of these FACTS is the improvement of security and efficiency of power transmission networks. Fast controllability in emergency situation provides increased flexibility and therefore stability and security advantages. The flexibility in control allows operating closer to stability limits and improve the efficiency of existing networks

1. International Journal of Advance Engineering and Research
Development
International Conference on Creativity and Innovation in Technology Development - 2018
Volume 5, Special Issue 05, March-2018 (UGC Approved)
Organized By SS College of Engineering, Udaipur 1
e-ISSN (O): 2348-4470
p-ISSN (P): 2348-6406
Scientific Journal of Impact Factor (SJIF): 5.71
FACTS Controllers for Power Flow Control: A Brief Review
Gourav Khusalani1
, Satyendra patel1
, Dheeraj Kumar Dhaked2
, Omveer Sharma3
1
PG Scholar, lectriccal and Electronics Engineering, NIT Tiruchirappalli
2
Research Scholar, School of Electrical Science, IIT Bhubaneswar, India.
3
Associat. Professor, Department of Electrical Engineering, RTU, Kota, Rajasthan, India.
Abstract: This paper provides a review of FACTS devices. The value of these FACTS is the improvement of security and
efficiency of power transmission networks. Fast controllability in emergency situation provides increased flexibility and
therefore stability and security advantages. The flexibility in control allows operating closer to stability limits and
improve the efficiency of existing networks.
I. INTRODUCTION
One of the major causes of voltage instability is the reactive power limits of the power systems. The many literatures
have proposed solutions for this problem, by using suitable location of Flexible AC Transmission Systems (FACTS) and
proper coordination between FACTS controllers to improve voltage stability of the power systems. Hence, improving the
systems reactive power handling capacity via Flexible AC transmission System (FACTS) device is a remedy for
prevention of voltage instability and hence voltage collapse. The several literatures are proposed the different
methods/techniques for enhancement of power system stability by placement of FACTS controllers, and coordination of
FACTS controllers, one of the shortcomings of such methods is that they only consider the normal state of system.
However, voltage collapses are mostly initiated by a disturbance (e.g. the outage of a line, or fault on system or
generation unit, or increased in load demand). So to locate FACTS devices, consideration of contingency conditions is
more important than consideration of normal state of system and some approaches are proposed to locate of FACTS
devices with consideration of contingencies.
II. Benefits of utilizing FACTS devices
The benefits of utilizing FACTS devices in electrical transmission systems can be summarized as follows [1]-[4]:
 Better utilization of existing transmissionsystem assets.
 Increased transmission system reliability and availability.
 Increased dynamic and transient grid stability and reduction of loop flows.
 Increased quality of supply for sensitive industries.
 Environmental benefits Better utilization of existing transmission system assets.
Table 1. Technical benefits of the main FACTS devices
III. TYPES of FACTS devices
There are different classifications for the FACTS devices. Depending on the type of connection to the network FACTS
devices can differentiate four categories:
• Series controllers
• Shunt controllers
Devices Load Flow
Control
Voltage
Control
Transient
Stability
Dynamic
Stability
SVC Good Best Good Better
STATCOM Good Best Better Better
TCSC Better Good Best Better
UPFC Best Best Better Better

2. International Journal of Advance Engineering and Research Development (IJAERD)
ICCITD-2018, Volume 5, Special Issue 05, March-2018
Organized By SS College of Engineering, Udaipur 2
• Series- series controllers
• Series- shunt controllers
Depending on technological features, the FACTS devices can be divided into two generations.
3.1 First generation
Uses thyristors with ignition controlled by gate (SCR).
3.2 Second generation
Uses semiconductors with ignition and extinction controlled by gate (GTO´s, MCTS, IGBTS, IGCTS, etc.).
These two classifications are independent, existing for example, devices of a group of the first classification that can
belong to various groups of the second classification. The main difference between first and second generation devices is
the capacity to generate reactive power and to interchange active power. The first generation FACTS devices work like
passive elements using impedance or tap changer transformers controlled by thyristors. The second generation FACTS
devices work like angle and module controlled voltage sources and without inertia, based in converters, employing
electronic tension sources fast proportioned and controllable and static synchronous voltage and current sources.
4.1 First Generation of FACTS
4.1.1. Static VAR Compensator (SVC)
A static VAR compensator (or SVC) is an electrical device for providing fast-acting reactive power on high-voltage
electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating
voltage and stabilising the system [6]. The term "static" refers to the fact that the SVC has no moving parts (other than
circuit breakers and disconnects, which do not move under normal SVC operation). Prior to the invention of the SVC,
power factor compensation was the preserve of large rotating machines such as synchronous condensers
.
Figure 1. Circuit for a Static VAR Compensator (SVC)
The SVC is an automated impedance matching device, designed to bring the system closer to unity power factor. If the
power system's reactive load is capacitive (leading), the SVC will use reactors (usually in the form of Thyristor-
Controlled Reactors) to consume VARs from the system, lowering the system voltage. Under inductive (lagging)
conditions, the capacitor banks are automatically switched in, thus providing a higher system voltage. They also may be
placed near high and rapidly varying loads, such as arc furnaces, where they can smooth flicker voltage. It is known that
the SVCs with an auxiliary injection of a suitable signal can considerably improve the dynamic stability performance of a
power system. It is observed that SVC controls can significantly influence nonlinear system behaviour especially under
high-stress operating conditions and increased SVC gains.

3. International Journal of Advance Engineering and Research Development (IJAERD)
ICCITD-2018, Volume 5, Special Issue 05, March-2018
Organized By SS College of Engineering, Udaipur 3
Figure 2. FACTS devices (a) TCSC, (b) SVC, and (c) UPFC
4.1.2.Thyristor-Controlled Series Capacitor (TCSC)
TCSC controllers use thyristor-controlled reactor (TCR) in parallel with capacitor segments of series capacitor bank.
TCSC is an effective and economical means of solving problems of transient, dynamic, steady state and voltage stability
in long transmission lines[7]. A TCSC is a series controlled capacitive reactance that can provide continuous control of
power on the ac line over a wide range. The functioning of TCSC can be comprehended by analysing the behaviour of a
variable inductor connected in series with a fixed capacitor.
4.1.3.Thyristor-Controlled Phase Shifter (TCPS)
In a TCPS control technique the phase shift angle is determined as a nonlinear function of rotor angle and speed.
However, in real-life power system with a large number of generators, the rotor angle of a single generator measured
with respect to the system reference will not be very meaningful.
4.2 Second Generation of FACTS
4.2.1. Static Compensator
The emergence of FACTS devices and in particular GTO thyristor-based STATCOM has enabled such technology to be
proposed as serious competitive alternatives to conventional SVC[5]. A static synchronous compensator (STATCOM) is
a regulating device used on alternating current electricity transmission networks. It is based on a power electronics
voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If
connected to a source of power it can also provide active AC power. It is a member of the FACTS family of devices.
Usually a STATCOM is installed to support electricity networks that have a poor power factor and often poor voltage
regulation. There are however, other uses, the most common use is for voltage stability.
4.2.1. Static Compensator
The emergence of FACTS devices and in particular GTO thyristor-based STATCOM has enabled such technology to be
proposed as serious competitive alternatives to conventional SVC [5]. A static synchronous compensator (STATCOM) is
a regulating device used on alternating current electricity transmission networks. It is based on a power electronics
voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If
connected to a source of power it can also provide active AC power. It is a member of the FACTS family of devices.
Usually a STATCOM is installed to support electricity networks that have a poor power factor and often poor voltage
regulation. There are however, other uses, the most common use is for voltage stability.
The emergence of FACTS devices and in particular GTO thyristor-based STATCOM has enabled such technology to be
proposed as serious competitive alternatives to conventional SVC5]. A static synchronous compensator (STATCOM) is a
regulating device used on alternating current electricity transmission networks. It is based on a power electronics voltage-
source converter and can act as either a source or sink of reactive AC power to an electricity network. If connected to a
source of power it can also provide active AC power. It is a member of the FACTS family of devices. Usually a
STATCOM is installed to support electricity networks that have apower factor and often poor voltage regulation. There
are however, other uses, the most common use is for voltage stability. (SSSC)
This device work the same way as the STATCOM. It has a voltage source converter serially connected to a transmission
line through a transformer. It is necessary an energy source to provide a continuous voltage through a condenser and to

4. International Journal of Advance Engineering and Research Development (IJAERD)
ICCITD-2018, Volume 5, Special Issue 05, March-2018
Organized By SS College of Engineering, Udaipur 4
compensate the losses of the VSC [8]. A SSSC is able to exchange active and reactive power with the transmission
system. But if our only aim is to balance the reactive power, the energy source could be quite small.
The injected voltage can be controlled in phase and magnitude if we have an energy source that is big enough for the
purpose. With reactive power compensation only the voltage is controllable, because the voltage vector forms 90º
degrees with the line intensity. In this case the serial injected voltage can delay or advanced the line current.
4.2.3. Unified Power Flow Controller (UPFC)
A unified power flow controller (UPFC) is the most promising device in the FACTS concept. It has the ability to adjust
the three control parameters, i.e. the bus voltage, transmission line reactance, and phase angle between two buses, either
simultaneously or independently. A UPFC performs this through the control of the in-phase voltage, quadrature voltage,
and shunt compensation[9]. The UPFC is the most versatile and complex power electronic equipment that has emerged
for the control and optimization of power flow in electrical power transmission systems. It offers major potential
advantages for the static and dynamic operation of transmission lines. The UPFC was devised for the real-time control
and dynamic compensation of ac transmission systems, providing multifunctional flexibility required to solve many of
the problems facing the power industry. Within the framework of traditional power transmission concepts, the UPFC is
able to control, simultaneously or selectively, all the parameters affecting power flow in the transmission line.
Alternatively, it can independently control both thereal and reactive power flow in the line unlike all other controllers.
Figure 3. UNIFIED power flow controller
V. APPLICATION OF FACTS IN INDIAN POWER SYSTEM
In India at the time of independence, the power supply was essentially locally oriented and the highest system voltage
was 132 kV. Subsequently, it rose to 220 kV and finally to 400 kV level. Also 800 kV transmission system has been
constructed, but charged at 400 kV level for operation at present. in India, a FACTS project has been undertaken in
September 2000 which is an in-house development effort on 400 kV line between Kanpur (Uttar Pradesh) and Ballabgarh
(Haryana) in the Northern Grid. The project is proposed to be implemented in two phases. Phase-I covers commissioning
of 35% Fixed Series Compensation (FSC) consisting of two banks of 27% and 8%. Phase-I1 covers commissioning of
Thyristor Controlled Series Capacitor (TCSC), under an R&D project.
By judiciously applying series compensation, active power transfer and reactive power consumption of the transmission
lines can be controlled application of series compensation on following 400 kV corridors were considered:
• Itarsi-Indore double circuit line
• Satpura-Indore line
• Bhilai-Satpura line
• Bhilai-Chandrapur double circuit line
• Bhilai-Satpura and Satpura-Koradi lines
• Vindhyachal-Jabalpur double circuit line
• Dadri-Malerkotla line
• Kanpur-Ballabhgarh line
VI. CONCLUSION
By using FACTS devices the load ability of power system increases, also there are always a maximum number of
FACTS devices beyond which the system load ability cannot be increased any further. When only one type of FACTS
device is used, the UPFC has the best performance and after it, SVC and TCSC respectively. Using two different types of

5. International Journal of Advance Engineering and Research Development (IJAERD)
ICCITD-2018, Volume 5, Special Issue 05, March-2018
Organized By SS College of Engineering, Udaipur 5
FACTS devices, the pair of SVC-UPFC has the best performance and after it, TCSC-UPFC and TCSC-SVC,
respectively. Simultaneous use of these three FACTS devices is the best option. The most studied cases from the
viewpoint of application are:
Voltage Control:SVC, UPFC, STATCOM, TCSC and TCPST/PST.
Assets Optimization: SVC, UPFC, STATCOM, TCSC, TCPST/PST and SSSC
Line Overload Limiting: UPFC, TCSC and TCPST/PST.
Avoid congestion and re-dispatch: UPFC, TCSC and SVC.
Voltage stability and collapse: STATCOM, UPFC, TCSC and SVC.
Angle stability: UPFC, TCSC, SVC and SSSC.
N-1 Contingency criteria fulfilment: UPFC, TCSC, SVC and STATCOM.
Transmission cost minimization: UPFC, TCSC, SVC, TCPST/PST, SSSC and STATCOM.
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