electricity is a highly engineered
FACTS product, it is increasingly being
considered and handled as a commodity.
Thus, transmission systems are being
pushed closer to their stability and
Document By thermal limits while
SANTOSH BHARADWAJ REDDY the focus on the quality of power
Email: help@matlabcodes.com delivered is greater than ever.In the
Engineeringpapers.blogspot.com evolving utility environment, financial
More Papers and Presentations available on above site
and marketforces are, and will continue
to, demand a more optimal andprofitable
ABSTRACT operation of the power system with
This paper provides a summary of respect to generation, transmission, and
one of the three planned presentations on distribution. Now, more than ever,
the topic of“ FACTS Fundamentals ,”for advanced technologies are aramount for
a session the reliableand secure operation of
Sponsored by the DC and FACTS power systems. To achieve both
Education Working Group, under the operational reliability and financial
DC and FACTS Subcommittee of the profitability, it has become clear that
T&D Committee. This paper is on Part I more efficient utilization and control of
of the session and focuses on a summary the existing transmission system
of the issues and benefits of applying infrastructure is required. Improved
FACTS controllers to AC power utilization of the existing power system
systems. The overall process for system is provided through the application of
studies and analysis associated with advanced control technologies. Power
FACTS installation projects and the need electronics based equipment, or Flexible
for FACTS controller models is also AC Transmission Systems (FACTS),
discussed. Finally, an introduction to the provide proven echnicalsolutions to
basic circuits of several FACTS address these new operating challenges
controllers is provided with a focus on being presented today. FACTS
their system technologies allow for improved
Performance characteristics. This paper transmission system operation with
is designed to be accompanied by the minimal infrastructure investment,
presentation material. Index Terms environmental impact, and
Flexible AC Transmission Systems, implementation time compared to the
FACTS, construction of new transmission
Power Electronic Equipment, Power lines.Traditional solutions to upgrading
System Stability, Power System Control. theelectrical transmission system
infrastructure have been primarily in the
I. INTRODUCTION form new transmission lines,
With the ongoing expansion and growth ubstations, and associatedequipment.
of the electric utility industry, including However, as experiences have proven
deregulation in many over the past decade or more, the process
countries,numerous changes are to permit, site, and construct new
continuously being introduced to a once transmission lines has become extremely
predictable business. Although difficult,expensive, time-consuming, and
controversial. FACTS technologies
1
provide advanced solutions as cost- When discussing the creation,
effective alternatives to new movement, and utilization of
transmission line construction. electrical power, it can be separated into
The potential benefits of FACTS three areas, which
equipment are now widely recognized by traditionally determined the way in
the power systems engineering and T&D which electric utility
communities. With respect to FACTS companies had been organized. These
equipment,voltage sourced converter are illustrated in
(VSC) technology, which utilizes self- Figure 1 and are:
commutated thyristors/transistors such as G eneration
GTOs, GCTs,IGCTs, and IGBTs, has Transmission
been successfully applied in a numberof Distribution
installations world-wide for Static
Synchronous Compensators
(STATCOM) [1-5], Unified Power
FlowControllers (UPFC) [6, 7],
Convertible Series Compensators(CSC)
[8], back-to-back dc ties (VSC-BTB) [9,
10] and VSCtransmission [11]. In
addition to these referenced and other
applications, there are several recently Although power electronic based
completedSTATCOMs in the U.S., in equipment is prevalent in each of these
the states of Vermont [12, 13],California three areas, such as with static excitation
[14], and Texas [no references systems for generators and Custom
available]. In addition, there are newly Power equipment in distribution systems
planned STATCOMs in Connecticut [23], the focus of this paper and
[15] and Texas, as well as a small accompanying presentation is on
STATCOM (D-VAR)planned for BC transmission, that is, moving
Hydro [16] and several other locations. the power from where it is generated to
Other installations of power electronic where it is utilized.
equipment includes Distributed
Superconducting Magnetic Energy B. Power System Constraints
Storage units(D-SMES) [17]. These As noted in the introduction,
aforementioned transmission system transmission systems are being pushed
installations are in addition to the earlier closer to their stability and thermal limits
generation of power electronics systems while the focus on the quality of power
that utilize linecommutated thyristor delivered is greater than ever. The
technology for Static Vac Compensators limitations of the transmission system
(SVC) [18] and can take many forms and may involve
Thyristor Controlled Series power transfer between areas
Compensators (TCSC) [19-22]. (referred to here as transmission
bottlenecks) or within a single area or
region (referred to here as a regional
II. CONTROL OF POWER SYSTEMS constraint) and may include one or more
A.Generation , Transmission , of the following characteristics:
Distribution : • Steady-State Power Transfer Limit
• Voltage Stability Limit
2
• Dynamic Voltage Limit
• Transient Stability Limit
• Power System Oscillation Damping
Limit
• Inadvertent Loop Flow Limit
• Thermal Limit
• Short-Circuit Current Limit
• Others
Each transmission bottleneck or regional
constraint may have one or more of these
system-level problems. The key to
solving these problems in the most cost-
effective and coordinated manner is by
thorough systems engineering
analysis, as described later in this paper.
C. Controllability of Power Systems
To illustrate that the power system only
has certain variables that can be
impacted by control, consider the basic
and well-known power-angle curve,
shown in Figure 2.
Although this is a steady-state curve and
the implementation of FACTS is
primarily for dynamic issues, this
illustration demonstrates the point that
there are primarily three main variables With the establishment of “what”
that can be directly controlled in the variables can be controlled in a power
power system to impact its performance. system, the next question is “how” these
These are: variables can be controlled. The answer
• Voltage is presented in two parts: namely
• Angle conventional equipment and FACTS
• Impedance controllers.
One could also make the point that direct Examples of Conventional Equipment
control of power is a fourth variable of For Enhancing
controllability in power systems. Power System Control
• Series Capacitor
-Controls impedance
• Switched Shunt-Capacitor and Reactor
-Controls voltage
• Transformer LTC
-Controls voltage
• Phase Shifting Transformer
-Controls angle
• Synchronous Condenser
-Controls voltage
• Special Stability Controls
3
-Typically focuses on voltage control but illustration of a few cycles of voltage at
can often power system
include direct control of power frequency. This figure shows that the
• Others (When Thermal Limits are speed of mechanical switches (primarily
Involved) circuit breakers) for conventional
-Can included reconductoring, raising equipment solutions can be as fast as a
conductors, couple of cycles of 60 (or 50) Hz. This
Dynamic line monitoring, adding new speed of switching in and of itself may
lines, etc. be
Example of FACTS Controllers for fast enough to solve many power system
Enhancing Power constraints.
System Control Although there is a vast improvement in
• Static Synchronous Compensator switching time from mechanical to
(STATCOM) power electronic based solutions (Figure
-Controls voltage 3illustrates that the speed of power
• Static Var Compensator (SVC) electronics switches is a fraction of a
-Controls voltage cycle), the main benefit that FACTS
• Unified Power Flow Controller controller solutions provide is the
(UPFC) cycling/repeatability” and “smooth
• Convertible Series Compensator (CSC) control” that accompanies the power
• Inter-phase Power Flow Controller electronic based switching. In other
(IPFC) words, a mechanically switched based
• Static Synchronous Series Controller (conventional) solution is usually a “one
(SSSC) and done” or “on or off” impact to the
-Each of the aforementioned (and power system in the time frame needed
similar) controllers impact voltage, for power system stability, whereas the
impedance, and/or angle (and power)• power electronic based solution can
Thyristor Controlled Series Compensator provide a smooth, continuous, and/or
(TCSC) repeatable option for power system
-Controls impedance control. Thus by applying power
• Thyristor Controlled Phase Shifting electronic based solutions to alleviate
Transformer (TCPST) power system constraints, it is not just
-Controls angle “speed” but “cycling” and “smooth
• Super Conducting Magnetic Energy control” that is gained.
Storage (SMES)
-Controls voltage and power
As mentioned earlier, the key to solving
transmission system problems in the
most cost-effective and coordinated
manner is by thorough systems analysis.
This includes comparing the system
benefits available by conventional
Equipment and from FACTS controllers.
There is an important distinction to make
when considering the differences in
these two solution options. Figure 3 is an
4
(magnitude and duration)
D. Benefits of Control of Power Systems • Transient Stability Criteria
Once power system constraints are • Power System Oscillation Damping
identified and through system studies -e.g., Minimum damping ratio
viable solutions options are identified, • Others
the benefits of the added power system
control must be determined. The
following offers a list of such benefits:
• Increased Loading and More Effective
Use of
Transmission Corridors
• Added Power Flow Control
• Improved Power System Stability
• Increased System Security
• Increased System Reliability
• Added Flexibility in Siting New IV.OVERVIEWOFFACTSCONTROLL
Generation ERCIRCUITS
• Elimination or Deferral of the Need for
New This section provides a sample of some
Transmission Lines of the FACTS controller circuits and
The advantages in this list are important system performance characteristics that
to achieve in the will be discussed during the presentation
overall planning and operation of power that accompanies this paper. The focus
systems. However, of the presentation will not be on the
for justifying the costs of implementing detail circuit topologies, but rather on the
added power system limitations and
control and for comparing conventional controllability of ac systems using the
solutions to FACTS FACTS controllers
controllers, more specific metrics of the
benefits to the power
system are often required. Such benefits
can usually be tied
back to an area or region for a specific
season and year at a
defined dispatch (usually given by an
ISO or equivalent) while
meeting the following criteria, for
example:
• Voltage Stability Criteria
-e.g., P-V voltage or power criteria with
minimum margins
-e.g., Q-V reactive power criteria with
minimum margins
• Dynamic Voltage Criteria
-e.g., Avoiding voltage collapse
-e.g., Minimum transient voltage dip/sag
criteria
5
along with its basic attributes and
configurations.
Unified
Power
Flow
Controller
Figure 9 shows the basic circuit for a
Unified Power Flow Controller (UPFC)
and Figure 10 shows a Static
Synchronous Series Compensator
(SSSC). Figure 11 shows the phasor
diagrams depicting the UPFC operation
and its impact on the power system, and
Figure 12 illustrates the control modes of
the series compensator (UPFC or SSSC)
(the characteristics of the shunt portion
of the UPFC is similar to Figure 8).
6
These, along with the V-- X phasor a focus on their system performance
characteristics will be characteristics. This paper was designed
Discussed in details in the presentation to be accompanied by the presentation
that will accompany this paper. Material.
REFERENCES
[1] S. Mori, K. Mistune, T. Hasegawa, S.
Ohnishi, M. Takeda, M. Soto,
S.Murakami, F. Ishiguro, “Development
of a Large Static Var Generator Using
Self-Commutated Inverters for
Improving Power System Stability,”
IEEE Transactions on Power Systems,
Vol. 8, No. 1, February, 1993, pp.371-
377.
[2] M. Hirakata, H. Somiya, Y. Mino, K.
Baba, S. Murakami, Y.
Watanabe,“Application of Self-
Thyristor Controlled Series
Compensator
Figure 13 shows the basic circuit for a
Thyristor Controlled Series Compensator
(TCSC). Figure 14 shows its
impedancecurrent (X-I) characteristics
for both a single-module and
Multi-module controllers. These will be
discussed in detail in the presentation Commutated Inverters to Substation
that will accompany this paper Reactive Power Control,” CIGRE Paper
23-205, Paris Session, 1996.8
SUMMARY
This paper provided a summary of one
of the three presentations on the topic of
“FACTS Fundamentals,” for a session
sponsored by the DC and FACTS
Education Working Group, under the
DC and FACTS Subcommittee of the
T&D Committee. This paper was on Part
I of the session and focused on a
summary of the issues and benefits of
[3] C. Schauder, M. Gerhardt, E. Stacey,
applying FACTS controllers to AC
T. Lemak, L. Gyugyi, T.W. Cease,
power systems. The overall process for
A. Edris, M. Wilhelm, “TVA
system studies and analysis associated
STATCOM Project: Design, Installation,
with FACTS installation projects and the
and Commissioning,” CIGRE Paper 14-
need for FACTS controller models was
106, Paris General Session, 1996.
also discussed. Finally, an introduction
[4] C. Schauder, “STATCOM for
to the basic circuits of several FACTS
Compensation of Large Electric Arc
controllers was provided with
7
Furnace Installations,” Proceedings of Proceedings of the 2001 IEEE PES
the IEEE PES Summer Power Summer Power Meeting, Vancouver,
Meeting, Edmonton, Alberta, July 1999, BC, July 2001
pp. 1109-1112.
[5] D.J. Hanson, C. Horwill, B.D.
Gemmell, D.R. Monkhouse, “A Document By
STATCOM-Based Reloadable SVC SANTOSH BHARADWAJ REDDY
Project in the UK for National Grid,” Email: help@matlabcodes.com
Proceedings of the IEEE PES Winter Engineeringpapers.blogspot.com
Power Meeting, New York, January More Papers and Presentations available on above site
2002.
[6] C. Schauder, E. Stacey, M. Lund, L.
Gyugyi, L. Kovalsky, A. Keri, A.
Mehraban, A. Edris, "AEP UPFC
Project: Installation, Commissioning and
Operation of The ±160 MVA
STATCOM (Phase I)," IEEE
Transactions
on Power Delivery Vol. 13, No. 4,
October 1998, pp. 1530-1535.
[7] B.A. Reno, A.J.F. Keri, A.S.
Mehraban, J.P. Kiesinger, C.D. Schaefer,
L. Gyugyi, L.J. Kowalski, A.A. Eddies,
“World’s First Unified Power Flow
Controller on the AEP System,” CIGRE
Paper 14-107, Paris Session, 1998.
[8] B. Fardanesh, M. Henderson, B.
Spelling, S. Salinger, L. Gyugyi,
C.Schauder, B. Lam, J. Mount ford, R.
Agape, A. Edris, “Convertible Static
Compensator Application to the New
York Transmission System,” CIGRE
Paper 14-103, Paris Session, 1998.
[9] H. Suzuki, M. Takeda, G. Reed,
“Application of Voltage Source
Converter
Technology to a Back-to-Back DC
Link,” Presented at the Panel Session
On FACTS Controllers: Applications
and Operational Experience,
Proceedings of the IEEE PES Summer
Power Meeting, Edmonton,
Alberta, July 1999.
[10] T. Larsson A. Edris, D. Kidd, F.
Aboytes, “Eagle Pass Back-to-Back Tie:
a Dual Purpose Application of Voltage
Source Converter Technology,”
