— A PPLI C ATI O N NOTE

SVC and STATCOMAn overview

SVC and STATCOM: An overview

SVC (Static Var Compensator) and STATCOM (Static Synchronous Compensator) are shunt devices in the FACTS family. The initial of the two, SVC, based on high power thyristor technology, appeared in the field in the 1970s. STATCOM, based on GTO (Gate Turn-off Thyristors) came into use in the 1980s, and subsequently, with high power IGBT (Insulated Gate Bipolar Transistor) becoming commercially avail-able, STATCOM based on this technology platform came on line in the 1990s.

As power demand is on the rise in most parts of the world, power transmission facilities need to keep up, as well. Building more power lines may not be the only or even the best way, however, as transmis-sion lines cost a lot of money, take considerable time to build, and are subject to lengthy permit pro-cedures and environmental constraints. With SVC and STATCOM, the power transmission capability of lines can be increased considerably. Squeezing more power out of existing lines can eliminate or at least postpone the need to build new lines, which all adds up to reduced environmental impact, and significant cost and time savings.

Developed and refined over the years in a number of ways, SVC is still ruling as the main controllable shunt compensation device. Simultaneously, STAT-COM is gaining momentum and is to an increasing

degree catching the interest of utilities looking for options that can offer additional benefits to those traditionally available, in particular where space in sub-stations is scarce, the reactive power output needs to be controllable more or less independent of the AC system voltage, or a speed of response one order of magnitude greater than what is possi-ble with thyristors is desired.

In fact, SVC or STATCOM should be the natural choice where the following qualities are required or desirable:• Rapid dynamic response• Ability for frequent variations in output• Output smoothly adjustable

Each in its own particular way, SVC and STATCOM of-fer benefits such as:• Grid voltage control under normal and contin-

gency conditions• Fast response reactive power following contingen-

cies• Preventing/reducing risk for voltage collapses in

the grid• Preventing over-voltages at loss of load• Boosting voltage during under-voltage distur-

bances and faults• Damping active power oscillations

—01 220 kV SVC Light, Chile.

(a) H-bridge cell with IGBTs (single phase)

TCR TSC TSC Harmonic filters

420 kV SVC, Norway• Increased power transfer capability, by stabilizing

the voltage in weak and/or heavily loaded points inthe grid

• Power quality improvement by load balancing,flicker mitigation and harmonic filtering

SVCSVC can be built using a variety of designs. However, the controllable elements used in most systems are similar. The commonly used controllable elements are:• Thyristor-controlled reactor (TCR)• Thyristor-switched capacitors (TSC)• Thyristor-switched reactor (TSR)

STATCOMSVC Light® is a STATCOM device, based on a chain-link modular multilevel (MMC) voltage source con-verter (VSC) concept, particularly adapted for power system applications. It is capable of yielding high re-active power input to the grid more or less unim-peded by suppressed grid voltages, and with high dynamic response. This is useful, for instance, to support more or less weak grids loaded by a large percentage of air conditioners in hot and humid cli-mates, and to improve the availability of large wind farms under varying grid conditions.

Insulated Gate Bipolar Transistors (IGBT) and Insu-lated Gate Commutated Thyrustirs (IGCT) are key components in SVC Light. The multilevel chain-link solution is built up by linking H-bridge modules in series with one another to form one phase leg of the VSC branch. (a) shows a single H-bridge with four IGBTs, and (b) shows a configuration in which four H-bridge modules make up each of the three phase legs.

SVC configuration: TCR/TSC/Harmonic filters

As TCR produces harmonics during operation, filters are required as parts of SVC design. When the SVC is required to safeguard power quality at the point of common connection in grids feeding heavy installa-tions such as railways, steel plants and mining com-plexes, additional harmonic filters usually need to be included in the SVC scheme.

SVC: a case exampleAs a result of large power demanding industry de-velopment in central Norway, the demand in the re-gion has increased dramatically and is expected to grow further. The power import capacity to the re-gion has previously been limited by the risk of volt-age collapse. As a remedy, two SVCs were installed in the existing power system. With the installation of the two SVCs, the power import capacity to the region has increased by up to 400 MW over the ex-isting lines.

SVC Light: Multilevel chain-link converter setup.

(b) 3-phase chain-link of H-bridges

Udc

Udc

Udc

Udc

Udc

Udc

Udc

Udc

Udc

Udc

Udc

Udc

+

-

+ -

+ -

+ -

+ -

+

-

+

-

+

-

+

-

+

-

+

-

+

-

—02 SVC Light: Multilevel chain-link converter setup.—03 220 kV SVC Light, Chile.

SVC Light is available for system voltages up to69 kV and converter ratings of up to -/+ 400 Mvar.For higher voltages, a step-down transformer isused to connect SVC Light to the grid. SVC Lightprovides a symmetrical operating range. For asym-metrical operations and in order to optimize perfor-mance, thyristor-switched reactors and capacitorsare operated in parallel to form hybrid solutions.

SVC Light: a current exampleIn Chile there is growing opposition to the construc-tion of new transmission infrastructure. As a conse-quence, Chile s main transmission owner and opera-tor had been investigating optimal ways to exploitexisting facilities to a higher degree. To this end, it

—02

—03

was decided to install an SVC Light with the aim of increasing the dynamic stability of the system and thereby allow more power to be transmitted through the grid. The SVC Light is located in the capital of Chile, where the greatest part of the load is concentrated. The tasks of the SVC Light are the following:• Regulate and control the 220 kV grid voltage under

normal steady-state and contingency conditions;• Provide dynamic, fast response reactive power fol-

lowing system contingencies, such as networkshort circuits and line or generator outages, par-ticularly during high power flow northwards;

• Enable an increase of the power transfer capabilityof the grid.

xxx

xxxx

xxx

—We reserve the right to make technical changes or modify the contents of this document without prior notice. With re-gard to purchase orders, the agreed par-ticulars shall prevail. ABB AG does not ac-cept any responsibility whatsoever for potential errors or possible lack of infor-mation in this document.

—

abb.com/facts

We reserve all rights in this document andin the subject matter and illustrations con-tained therein. Any reproduction, disclo-sure to third parties or utilization of itscontents – in whole or in parts – is forbiddenwithout prior written consent of ABB AG.Copyright© 2019 ABBAll rights reserved