By Kathleen Davis, Senior Editor
Commonly called STATCOMs, static synchronous compensators were introduced in the 1990s as a way to help electric arc furnaces and steel processing facilities mitigate voltage flicker and other power quality problems.
Today, they’re most often used to help smooth the deployment of something distinctly more green than steel—renewable energy.
American Superconductor (AMSC), a STATCOM technology provider, sold in 2002 its first STATCOM in the renewables area to the Foote Creek Wind Farm in Wyoming.
Since then, its market share for STATCOMs has grown significantly in the renewables framework, said Tim Poor, AMSC senior vice president of global sales and business development.
AMSC has sold more than 70 D-VAR STATCOM systems worldwide, and most are being used in applications that connect vacillating renewables to the grid. The company’s STATCOM customers include more than 20 electric utilities and more than 45 wind farms.
“Renewables are, indeed, our biggest STATCOM customer,” Poor said. “The rate of growth in that area is just phenomenal.”
But STATCOMs offer benefits to smart grid areas as well, not just renewables integration.
“Without proper voltage, power’s not going to flow down the line,” Poor said. “Voltage is an absolute key parameter that makes the grid work.”
Renewables and Beyond
STATCOMs are a type of flexible alternating current transmission system (FACTS) device that use power semiconductors. AMSC developed, patented, produces and sells a dynamic volt amperes—reactive, or D-VAR, STATCOM system.
Speed makes STATCOMs the answer in stabilizing voltage as it moves across the grid. STATCOMs are “very, very fast,” Poor said.
They operate nearly in real time. They monitor and then correct voltage issues quickly. In addition, because they operate as a current source, STATCOMS are uniquely able to provide robust compensation to the grid.
“Mechanically switched devices such as capacitor banks are often just not fast enough in compensating for voltage,” Poor said. “D-VAR requires no human intervention and operates in the blink of an eye to support the grid.”
If left uncorrected for long periods, voltage disturbances can lead to blackouts similar to the one in New York and the northeastern U.S. in 2003. According to government analysis, it was caused by issues related to voltage control and stability.
Sometimes humans and conventional grid equipment such as capacitor banks don’t react fast enough to prevent voltage collapse.
A STATCOM’s constant, real-time monitoring and reaction speed can prevent that voltage collapse from causing a domino effect and taking down a city, county or region.
STATCOM technology isn’t necessarily the most widely deployed FACTS technology for standard utility transmission grid support, Poor said.
D-VAR Statcoms are by far, however, the most common type of FACTS compensation used for connecting renewables, particularly wind farms, to the grid.
A big driver for wind farms linking in with STATCOMs is the interconnection requirements established by grid operators to ensure high grid reliability.
Canada, Australia, Spain, the U.K. and New Zealand have grid interconnection requirements for wind farms that require dynamic compensation, which can be provided by STATCOM technology. China and India are considering similar legislation.
In the U.S., wind farms must rely on a site-specific, system-impact study to determine the interconnection requirements.
While that doesn’t always mean a STATCOM is required, the study dictates the optimal requirements specific to each wind farm and connection point. While STATCOM technology has matured where it is economic and reliable, the technology is still not as widely deployed as it could be, Poor said.
“Many utilities have limited experience with FACTS devices and particularly STATCOMs,” Poor said. “Rather than using large-scale SVCs (static voltage compensators) to address regional transmission grid issues, often a distributed STATCOM or SVC solution is just as effective, less costly and more reliable.
“Don’t get me wrong, large transmission SVCs are an important tool in the toolbox, but too often they are the only solution considered.”
AMSC offers SVCs and STATCOMs for voltage compen-sation, but Poor stressed that utilities shouldn’t necessarily lock themselves into a single, traditional approach when seeking to resolve voltage issues.
“We encourage utilities to start with a basic grid performance specification and then evaluate different technologies and solutions based on their ability to solve the problem,” he said.
Getting Started on the STATCOM Path
Utilities are always developing contingency planning or what-if scenarios, Poor said. They anticipate problems before they occur using sophisticated simulation programs and often uncover voltage issues.
This is the point where they should begin looking into details, discretely modeling by load type to see what’s causing the issue. Knowing the cause of a potential voltage issue is essential when considering solution options, including SVCs and STATCOMs.
STATCOMs, like D-VAR, are a current source that generates reactive power. SVCs are not.
Based on capacitors, an SVC’s ability to support the grid drops by the square of the voltage vs. a STATCOM whose output is affected only linearly by voltage.
The answer to a utility’s problem, therefore, might depend on the details of the problem itself.
Some situations might be adequately addressed with SVCs; others might lend themselves more toward a STATCOM solution.
Poor gave an example with Northeast Utilities. The company had an issue in Connecticut, a limitation on the line that was caused by voltage instability.
It employed AMSC’s D-VAR and, as a result, raised the capacity limit of the line by 100 MW.
The utility was ecstatic with the results because it meant that the fix virtually paid for itself in one summer, Poor said. (See sidebar for more D-VAR solutions.)
Knowing whether you need a STATCOM or an SVC or any voltage solution requires system studies, he said.
It’s all about accurately defining the problem and then optimizing the solution.
Technology like STATCOMs might seem expensive, but most utilities can’t afford not to correct the voltage disruptions that often put their systems at risk.
Significant American Superconductor STATCOM installations
Long Island Power Authority
- problem: power flows the length of the island, which can lead to load instability
- solution: 36 mega volt amperes—reactive (MVAR) of base-rated D-VAR
- total dynamic range of reactive compensation: -96 to +240 MVAR to protect grid stability
- one of the larger STATCOMs installed in North America
Chifeng Project, Inner Mongolia, China
- problem: 600 MW from seven wind farms meeting at one point on the grid; dynamic reactive compensation requirements for a 220 kV grid
- solution: 16 MVAR D-VAR system
- American Superconductor’s first STATCOM application in China
Basin Electric Cooperative
- problem: sizeable transmission grid with lots of mining, which means lots of pumps and motors to stress the grid
- solution: steady state and transient voltage support with 34 MVAR D-VAR
- short-term rating of 91 MVAR
- one of the largest STATCOMs ever deployed in the North American transmission grid
- expected online by end of 2009
More PowerGrid International Issue Articles
PowerGrid International Articles Archives