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Flexible AC transmission system

 

 
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A Flexible Alternating Current Transmission System (FACTS) is a system comprised of static equipment used for the AC
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 transmission of electrical energy
Electric power transmission

Electric power transmission is the bulk transfer of electrical power , a process in the delivery of electricity to consumers. A power transmission grid typically connects power plants to multiple Electrical substation near a populated area....
. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics
Power electronics

Power electronics is the applications of solid-state electronics for the control and conversion of electric power...
-based device.

FACTS 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 controllability and increase power transfer capability."

S could be connected:

eries compensation, the FACTS is connected in series with the power system.






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Encyclopedia


A Flexible Alternating Current Transmission System (FACTS) is a system comprised of static equipment used for the AC
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 transmission of electrical energy
Electric power transmission

Electric power transmission is the bulk transfer of electrical power , a process in the delivery of electricity to consumers. A power transmission grid typically connects power plants to multiple Electrical substation near a populated area....
. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics
Power electronics

Power electronics is the applications of solid-state electronics for the control and conversion of electric power...
-based device.

FACTS 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 controllability and increase power transfer capability."

FACTS technology

FACTS could be connected:
  • in series with the power system (series compensation)
  • in shunt with the power system (shunt compensation)
  • both in series and in shunt with the power system


Series compensation

In series compensation, the FACTS is connected in series with the power system. It works as a controllable voltage source.

Series inductance
Inductance

Inductance is the property in an electrical circuit where a change in the current flowing through that circuit induces an Electromotive force that opposes the change in current ....
 occurs in long transmission lines, and when a large current flow causes a large voltage drop. To compensate, series capacitors are connected.

Shunt compensation

In shunt compensation, power system is connected in shunt
Shunt (electrical)

In electronics, a shunt is a device which allows electric current to pass around another point in the electrical network. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage....
 with the FACTS. It works as a controllable current source
Current source

A current source is an electrical or electronic device that delivers or absorbs electric current. A current source is the Duality of a voltage source....
.

Shunt compensation is of two types:

Shunt capacitive compensation

This method is used improve the power factor
Power factor

The power factor of an alternating current electric power system is defined as the ratio of the AC power flowing to the load to the AC power , and is a number between 0 and 1 ....
. 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
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
. The net result is improvement in power factor.

Shunt inductive compensation

This method is used either when charging the transmission line
Transmission line

A transmission line is the material Transmission medium or structure that forms all or part of a Course from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission....
, 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
Ferranti effect

The Ferranti Effect is a rise in voltage occurring at the receiving end of a long transmission line, relative to the voltage at the sending end, which occurs when the line is charged but there is a very light load or the load is disconnected....
). 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.

FACTS theory


In the case of 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 that depends on line reactance X.





As it is a no-loss line, active power P is the same at any point of the line:

Reactive power at sending end is the opposite of reactive power at receiving end:

As is very small, active power mainly depends on whereas reactive power mainly depends on voltage magnitude.

Series compensation

FACTS for series compensation modify line impedance: X is decreased so as to increase the transmittable active power. However, more reactive power must be provided.



Shunt compensation


Reactive current is injected into the line to maintain voltage magnitude. Transmittable active power is increased but more reactive power is to be provided.



Examples of FACTS for series compensation


  • Static Synchronous Series Compensator (SSSC)
  • Thyristor Controlled Series Capacitor (TCSC): a series capacitor
    Capacitor

    A capacitor or condenser is a Passive component electronic component consisting of a pair of electrical conductor separated by a dielectric....
     bank is shunted by a thyristor
    Thyristor

    The thyristor is a Solid state semiconductor device with four layers of alternating N-type semiconductor and P-type semiconductor material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased ....
    -controlled reactor
    Inductor

    An inductor is a Passive component Electronic component that can store energy in a magnetic field created by the electric current passing through it....
  • 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 FACTS for shunt compensation


  • Static Synchronous Compensator (STATCOM
    STATCOM

    A STATCOM or Static Synchronous Compensator 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....
    ) previously known as a Static Condenser (STATCON)
  • Static VAR compensator
    Static VAr compensator

    A Static VAR Compensator is an electricity device for providing fast-acting reactive power compensation on high-voltage Electric power transmission networks....
     (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.


See also


Internal links

  • HVDC


External links

  • website.