Just the FACTS, ma'am

Phil Carson | Jun 09, 2010

 

Today we plunge into the world of flexible AC transmission, or FACTS.

Our guide is Greg Reed, director of the power and energy initiative at, and an associate professor in, the electrical and computer engineering department at the Swanson School of Engineering, University of Pittsburgh. (Errors in translation are mine.)

FACTS can be applied to existing transmission systems and new infrastructure to increase transmission system efficiency and eliminate congestion, effectively increasing capacity. It also enables the integration of more renewable resources.

Proponents of FACTS point to its environmental qualities: no rotating machinery, low maintenance, no use of oil or hazardous materials. And it often fits within the existing footprint of utility substations where one type of FACTS is typically located.

FACTS "secret sauce" lies in its power electronics, enabled by new semiconductor technologies, Reed told me. Power electronics' ability to convert an energy source into a form of compensation to the grid is key to FACTS' functionality.

FACTS essentially provide VAR (Volt Amperes Reactive) compensation at strategic points. One example is a long transmission corridor. Say electricity is generated at Point A - megawatts and mega-VARs - sending out 100 percent of rated voltage onto the grid. As those megawatts and mega-VARs travel across transmission lines, real and reactive losses occur.

As that power reaches Point B, near the end-user, total power falls below 100 percent of output. And efficiency has been lost, in real megawatts, and in mega-VARs that help deliver the voltage. FACTS at Point B can provide mega-VARs to boost voltage back to 100 percent.

In reality, FACTS typically is placed in two different locations, depending on whether the grid is simple or complex.

One location is close to the end-user on the transmission system, just before voltage is stepped down by a transformer to a radial distribution system. On large, complex, networked transmission systems in the United States, a FACTS device may be placed midway to relieve congestion.

The FACTS' sophisticated controls read the grid at its location in real-time and when a fault occurs, those controls will trigger a commensurate level of compensation. Thus FACTS devices provide a "first line of defense" in responding to system disturbances, both in a steady state sense and in a dynamic sense.

"Dynamic," of course, refers to the events on power grids that happen very rapidly, within milliseconds. This is where power electronics shine, as opposed to mechanical devices, because the former enable reaction time on orders of magnitude faster than electro-mechanical switches.

"That's really important," Reed pointed out. "If you're relying on mechanical devices to mitigate a disturbance, they may take too long, allowing the disturbance to range beyond control. The speed capability of FACTS devices allows us to respond to these fast disturbances dynamically so that they do not perturbate into larger situations."

"Not only does that build an extra level of intelligence into the grid, through automation and control, if set up correctly it can also do things like reduce system losses by making better decisions on how we operate the network on a real-time basis," Reed explained. "Those things are very hard for a human sitting at an operator's desk to keep an eye on."

And what about grid operators and the integration of FACTS into their system?

"They can see everything in its present state," Reed said. "They can monitor the FACTS device in real-time. And almost all of them have a manual override for direct control, should the operator wish the FACTS device to behave in a manner it would not do on its own."

"The human interface is important," Reed added. "One thing we've seen when a utility gets experience with FACTS equipment is that the operators initially tend to be somewhat skeptical of how the technology works on the system. After operators gain experience, they become the biggest proponents of the technology."

Okay, I've tried to keep this train on the track and avoid veering off into the weeds. If you've got a FACTS program going, let me know. I'm aware of a half-dozen around the country and over the summer I hope to feature several use cases to illustrate various applications of this technology.

As always, let us know your thoughts.  

Phil Carson
Editor-in-chief
Intelligent Utility Daily
pcarson@energycentral.com
303-228-4757