01-07-2013, 04:21 PM
Facts about Flexible AC Transmission Systems (FACTS) Controllers: Practical Installations and Benefits
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ABSTRACT
This paper presents various facts related to the
landmark development: practical installations, benefits
and application of FACTS controllers in the electric
utilities. The history of development of these devices is
presented along with the information regarding the first
utility installation/demonstration of FACTS devices. A
comprehensive collection of major FACTS installations
around the world is then presented. The paper also
analyses the benefit that can be achieved and cost
associated with these devices. The paper also presents
various applications that FACTS devices can have in the
deregulated market. Various issues related with the
FACTS controllers are also presented. The problem of
high losses of advanced FACTS controllers as compared
to conventional counterpart and need to take into
account of interaction among controllers in future power
system is highlighted. One real world example of each
major FACTS controller is presented and analysed in
the paper.
INTRODUCTION
The AC transmission system has various limits classified
as static limits and dynamic limits [1-3]. These inherent
power system limits restrict the power transaction, which
lead to the under utilization of the existing transmission
resources. Traditionally, fixed or mechanically switched
shunt and series capacitors, reactors and synchronous
generators were being used to solve much of the
problem. However, there are restrictions as to the use of
these conventional devices. Desired performance was
not being able to achieve effectively. Wear and tear in
the mechanical components and slow response were the
heart of the problems. There was greater need for the
alternative technology made of solid state devices with
fast response characteristics. The need was further
fuelled by worldwide restructuring of electric utilities,
increasing environmental and efficiency regulations and
difficulty in getting permit and right of way for the
construction of overhead transmission lines [4]. This,
together with the invention of Thyristor switch
(semiconductor device), opened the door for the
development of power electronics devices known as
Flexible AC Transmission Systems (FACTS)
controllers.
HISTORY OF DEVELOPMENT AND STATUS
STATIC VAR COMPENSATOR
Static Var Compensator is the most primitive and first
generation of FACTS controllers. Electric Power
Research Institute (EPRI) brings this technology to the
market three decade ago. This compensator consists of a
fast thyristor switch controlling a reactor and/or shunt
capacitor bank, to provide dynamic shunt compensation.
More than 800 SVCs are being installed worldwide, both
for utility and industrial (especially in electric arc
furnace and rolling mills) application. Even the utilities
in developing countries took the benefit of SVCs since
its invention. ABB remains the pioneer in deployment of
SVC and has supplied 55% of the total installation of
which 13% were being installed in Asian countries. The
world’s first demonstration of SVC for utility application
was installed in 1974, which was commercialized by
General Electric (GE) [1].
As a consequence of deregulation in UK in 1990,
voltage control became difficult. To accommodate the
risk associated with the uncertain future and changing
power system condition, UK installed relocatable SVC
(RSV). At present 12 RSVC (60 MVAr each) are
operational in the NGC (National Grid Company)
system [5].
THYRISTOR CONTROLLED SERIES CAPACITOR
Thyristor Controlled Series Capacitor (TCSC) is a later
member of the first generation of FACTS devices, that
uses silicon controlled rectifiers to manage a capacitor
bank connected in series with a line. TCSC allows utility
to transfer more power further on a particular line. The
worlds first three phase TCSC was developed by ABB
and installed at Kayenta substation, Arizona in 1992,
that raises the capacity of a transmission line by almost
30%. By the end of year 2004, seven TCSCs have been
installed worldwide. In Asia, three TCSC came into
operation; two in China and one in India, bringing Asia
into the forefront of the advanced FACTS technology.
Table 1 shows the complete list of TCSC installed
worldwide as of December 2004.
CONVERTIBLE STATIC COMPENSATOR
The most recent development in the field of FACTS
controllers is the “Convertible Static Compensators
(CSC)”. The CSC offers the full flexibility by allowing
its converters to be connected in shunt (STATCOM), in
series (SSSC), in shunt/series (UPFC) or in series/series
Interline Power Flow Controller (IPFC) with two lines.
The worlds first CSC is installed at New York Power
Authority’s Marcy 345 kV substation, which is capable
of operating in eleven different control modes.
CONGESTION MANAGEMENT
Congestion management is a serious concern for
Independent System Operator (ISO) in present
deregulated electricity markets as it can arbitrarily
increase the prices and hinders the free electricity trade.
FACTS devices like TCSC, TCPAR (Thyristor
Controlled Phase Angle Regulator) and UPFC can help
to reduce congestion, smoothen locational marginal
prices (LMP) and to increase the social welfare by
redirecting power from congested interface to under
utilized lines [7-8].
ATC IMPROVEMENT
In many deregulated market, the power transaction
between buyer and seller is allowed based on calculation
of ATC. Low ATC signifies that the network is unable to
accommodate further transaction and hence does not
promote free competition. FACTS controllers like
TCSC, TCPAR and UPFC can help to improve ATC by
allowing more power transactions [9-10].
CONCLUSIONS
With the history of more than three decades and
widespread research and development, FACTS
controllers are now considered a proven and mature
technology. The operational flexibility and
controllability that FACTS has to offer will be one of the
most important tools for the system operator in the
changing utility environment. In view of the various
power system limits, FACTS provides the most reliable
and efficient solution. The high initial cost has been the
barrier to its deployment, which highlight the need to
device proper tools and methods for quantifying the
benefits that can be derived from use of FACTS.