A static synchronous compensator (STATCOM), originally known as a static synchronous condenser (STATCON), is a regulating device shunt-connected to

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

electricity

transmission network Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is ...

. It is based on a

power electronics Power electronics is the application of electronics to the control and conversion of electric power. The first high-power electronic devices were made using mercury-arc valves. In modern systems, the conversion is performed with semiconducto ...

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 A flexible alternating current transmission system (FACTS) is a system composed of static equipment used for the alternating current (AC) transmission of electrical energy. It is meant to enhance controllability and increase power transfer capabi ...

family of devices, that became possible in 1990s due to availability of powerful

gate turn-off thyristor A gate turn-off thyristor (GTO) is a special type of thyristor, which is a high-power (.e.g. 1200V AC) semiconductor device. It was invented by General Electric. GTOs, as opposed to normal thyristors, are fully controllable switches which can be ...

s (GTO). STATCOM is inherently modular and electable. These compensators can also be used to reduce voltage fluctuations.

History and uses

A prototype 1 MVAr STATCON was described in a report by Empire State Electric Energy Research Corporation in 1987. The first production 100 MVAr STATCON made by

Westinghouse Electric The Westinghouse Electric Corporation was an American manufacturing company founded in 1886 by George Westinghouse. It was originally named "Westinghouse Electric & Manufacturing Company" and was renamed "Westinghouse Electric Corporation" in ...

was installed at the

Tennessee Valley Authority The Tennessee Valley Authority (TVA) is a federally owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, and small areas of Georgia, North Carolina ...

Sullivan substation in 1995 and was quickly retired due to obsolescence of its components. Usually a STATCOM is installed to support electricity networks that have a poor

power factor In electrical engineering, the power factor of an AC power system is defined as the ratio of the '' real power'' absorbed by the load to the ''apparent power'' flowing in the circuit. Real power is the average of the instantaneous product of v ...

and often poor

voltage regulation In electrical engineering, particularly power engineering, voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component, such as a transmission or distribution line. Voltage regulation desc ...

. There are however, other uses, the most common use is for voltage stability.

Construction and operation

A STATCOM is a

voltage source converter An HVDC converter converts electric power from high voltage alternating current (AC) to high-voltage direct current (HVDC), or vice versa. HVDC is used as an alternative to AC for transmitting electrical energy over long distances or between AC powe ...

(VSC)-based device, with the voltage source behind a reactor (STATCOM is connected to the utility grid via a transformer). The voltage source is created from a DC

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

and therefore a STATCOM has very little active power capability. However, its active power capability can be increased if a suitable energy storage device is connected across the DC capacitor. The reactive power at the terminals of the STATCOM depends on the amplitude of the voltage source. For example, if the terminal voltage of the VSC is higher than the AC voltage at the point of connection, the STATCOM generates reactive current (appears as a capacitor); conversely, when the amplitude of the voltage source is lower than the AC voltage, it absorbs reactive power (appears as an inductor). A

voltage droop Voltage droop is the intentional loss in output voltage from a device as it drives a load. Adding droop in a voltage regulation circuit increases the headroom for load transients. All electrical systems have some amount of resistance between t ...

of 1-10% (usually 3%) is built into STATCOMs.

STATCOM vs. SVC

A static VAR compensator (SVC) can also be used to maintain the voltage stability. STATCOM is costlier than an SVC (in part due to higher cost of the GTO thyristors) and exhibit higher losses, but has few technical advantages. As a result, the two technologies coexist. The response time of a STATCOM is shorter than that of a SVC, mainly due to the fast switching times provided by the

IGBT An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch, which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating lay ...

s of the voltage source converter (

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...

s cannot be switched off in a controlled fashion). As a result, the reaction time of a STATCOM is one to two cycles vs. two to three cycles for an SVC. The STATCOM also provides better reactive power support at low AC voltages than an SVC, since the reactive power from a STATCOM decreases linearly with the AC voltage (the current can be maintained at the rated value even down to low AC voltage), as opposed to power being a function of a square of voltage for SVC. The SVC is not used in a severe undervoltage conditions (less than 0.6 pu), since leaving the capacitors on can worsen the transient overvoltage once the fault is cleared, while STATCOM can operate until 0.2-0.3 pu (this limit is due to possible loss of synchronicity and cooling). The footprint of a STATCOM is smaller, as it does not need external inductors and large capacitors used by an SVC.

References

Sources

* * {{cite book , first1 = Kalyan K. , last1 = Sen , first2 = Mey Ling , last2 = Sen , date = 13 December 2021 , title = Power Flow Control Solutions for a Modern Grid Using SMART Power Flow Controllers , publisher = John Wiley & Sons , pages = , isbn = 978-1-119-82438-1 , oclc = 1268120186 , url = https://books.google.com/books?id=5NNUEAAAQBAJ&pg=RA1-PA15

External links

Conceptual survey of Generators and Power Electronics for Wind Turbines
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