FACT
(FLEXIBLE A.C. TRANSMISSION SYSTEM)
INTRODUCTION:
FACTS A flexible alternating current
transmission system (FACTS) is a system composed of static equipment used
for the AC transmission of electrical energy. It is meant to enhance controllability
and increase power transfer capability of the network. It is generally
a power electronics -based system.
A FACT is defined by the
IEEE as "a power electronic based system and other static equipment
that provide control of one or more AC transmission system parameters to
enhance control-ability and increase power transfer capability.
For a time being let us forget the
word FLEXIBLE, we are left with A.C Transmission System. In power system, there
are various stages like Generation, Transmission & Distribution.
Transmission can be done in both A.C & D.C. We are all aware of the
advantages & disadvantages of A.C & D.C transmission system but all
over it is seen that D.C transmission system has an upper hand over A.C
transmission system due to numerous reasons.
In-spite of this in Northern Oregon,
the 1st FACTS installation was adopted at the C.J. Slatt
sub-station. The answer is hidden in the word “FLEXIBLE”. FACTS technology can
be used to optimize existing electrical transmission system & provides
flexibility to it.
At present, electrical demands are
not steady, but fluctuate widely with customer needs. Static transmission lines
cannot quickly adapt to these changes which result in voltage losses to
customers. Reduced voltages & blowouts can also damage equipment. FACTS
technology includes software that responds to changing utility conditions &
optimizing system performance.
ABOUT
FACTS:
A flexible A.C. transmission system
(FACTS) is a combination of hardware and software installed in power transmission
substations designed to improve capacity and reliability. AC refers to
alternating current the electrical power supplied by electrical utilities to
homes and businesses. FACTS technology can be used to optimize existing
electrical transmission systems and often prevent or delay construction of new
transmission systems.
Electric utilities face continued
demands for greater capacity as customers consume greater quantities of
electricity. Conservation programs, higher efficiency appliances and lighting,
and smarter consumer electronics can slightly reduce electrical use.
Environmental concerns for overhead electrical lines, magnetic fields and
damage from new construction can delay new equipment construction. A flexible
AC transmission system can provide better performance of existing transmission
lines, improve power quality and reduce electrical losses.
Installation of FACTS equipment in
series, or in-line, with the transmission lines is used to control system
voltage. Equipment designed in shunt, or parallel across transmission lines,
controls current or electrical flow. FACTS include software, capacitors,
voltage regulators and other equipment that manages the electrical system.
Increasing development and
population density can make construction of new transmission equipment
difficult. FACTS technology is compact and can be installed within the existing
footprint of a substation or electric transmission facility. Existing
transmission lines carry higher loads without overheating or exceeding their rated
power limits. Customers typically see improved electric supply quality and
reliability.
FACTS technology helps us to provide
uninterrupted flow of power as is not possible in case of D.C. system &
thus the installation of rectifiers, inverters; D.C. switchgear & circuit
breakers are obsolete & does not cause harmonics injection in the system.
It improves the capacity of existing electrical transmission system.
TYPES
OF FACTS:
- Series Compensation
- Shunt Compensation
Examples
of series compensation-
- Static synchronous series compensator (SSSC)
- Thyristor-controlled series capacitor (TCSC): a series
capacitor bank is shunted by a thyristor-controlled reactor
- Thyristor-controlled series reactor (TCSR): a series
reactor bank is shunted by a thyristor-controlled reactor
- Thyristor-switched series capacitor (TSSC): a series
capacitor bank is shunted by a thyristor-switched reactor
- Thyristor-switched series reactor (TSSR): a series
reactor bank is shunted by a thyristor-switched reactor
Examples of shunt compensation-
- Static synchronous compensator (STATCOM); previously
known as a static condenser (STATCON)
- Static VAR compensator (SVC). Most common SVCs are:
- Thyristor-controlled reactor (TCR): reactor is
connected in series with a bidirectional thyristor valve. The thyristor
valve is phase-controlled. Equivalent reactance is varied continuously.
- Thyristor-switched reactor (TSR): Same as TCR but
thyristor is either in zero- or full- conduction. Equivalent reactance is
varied in stepwise manner.
- Thyristor-switched capacitor (TSC): capacitor is
connected in series with a bidirectional thyristor valve. Thyristor is
either in zero- or full- conduction. Equivalent reactance is varied in
stepwise manner.
- Mechanically-switched capacitor (MSC): capacitor is
switched by circuit-breaker. It aims at compensating steady state
reactive power. It is switched only a few times a day.
WORKING
OF FACTS:
- Series compensation
In series compensation, the FACTS
are connected in series with the power system. It works as a controllable
voltage source. Series inductance exists in all AC transmission
lines. On long lines, when a large current flows, this causes a large voltage
drop. To compensate, series capacitors are connected, decreasing the effect of
the inductance.
- Shunt compensation
In shunt compensation, power system
is connected in shunt (parallel) with the FACTS. It works as a
controllable current source. Shunt compensation is of two types:
- Shunt capacitive compensation
This method is used to improve
the power factor. Whenever an inductive load is connected to the
transmission line, power factor lags because of lagging load current. To
compensate, a shunt capacitor is connected which draws current leading the
source voltage. The net result is improvement in power factor.
- Shunt inductive compensation
This method is used either when
charging the transmission line, or, when there is very low load at the
receiving end. Due to very low, or no load – very low current flows
through the transmission line. Shunt capacitance in the transmission line
causes voltage amplification (Ferranti Effect). The receiving end voltage may
become double the sending end voltage (generally in case of very long
transmission lines). To compensate, shunt inductors are connected across the
transmission line. The power transfer capability is thereby increased depending
upon the power equation.
ADVANTAGES
OVER STANDARD TRANSMISSION SYSTEM:
A flexible AC transmission system
has several advantages over standard transmission networks. Existing
transmission lines have significant voltage losses over long distances. This
system can boost line voltage and maintain proper supply voltage
across a transmission network. Most transmission systems are interconnected
networks of supply lines, where power imbalances can occasionally occur. FACTS
shunt systems can balance power across parallel supply lines to optimize
performance. Increasing development and population density can make
construction of new transmission equipment difficult. FACTS technology is
compact and can be installed within the existing footprint of a substation or
electric transmission facility. FACTS technology includes software that
responds to changing utility conditions, optimizing system performance.
The superiority of FACTS over
present transmission system can be briefed as under. They are-
- Reliable
- Compact
- Simpler in construction & design
- Reduction in construction time
- Cheaper
- Reduced voltage loss
- Prevents harmonics injection in the system
- Maintain proper line voltage
- System efficiency is high
FACTS
CONCLUSION:
Now a day, there are so many scopes
for using FACT system. The population is increasing, for extra loads, FACTS is
needed to increase system performance and efficiency. In this presentation, the
FACTS & FACTS Controllers are discussed. In India, there is a bright chance
to use FACTS Technology in National Grid system. This technology improves the
power transfer capability as well as stability of the power system.
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