by Dan Ware
For many people, there’s nothing more annoying than when the power goes out. Sometimes the outage is mercifully brief, but other times, depending on the cause, they can last for hours or even days.
A new report from Sandia highlights advances in technology developed to improve the stability of large power systems, which will improve grid reliability, reduce the likelihood of a large power outage, and potentially reduce electricity costs by increasing power flow limits on congested transmission lines.
As part of a joint project with Montana Technological University and Bonneville Power Administration, Sandia researchers have developed a new damping control system that will further aid energy providers by increasing the stability margins with respect to inter-area oscillations. When demand for power is especially high, these oscillations become less damped, potentially leading to outages.
“As more power is needed to meet high demand in areas such as heavily populated Southern California, large amounts of power need to be transferred from high-supply regions like the Pacific Northwest with its abundance of hydroelectric power,” said Sandia’s David Schoenwald, who is the project principal investigator and coauthor of the report. “This involves the delivery of power over long transmission lines, which stretch for hundreds of miles.”
As more power is transferred from one region of the grid to another, the frequency levels of each region start to oscillate against each other, much like the up-and-down motion of a teeter-totter. These oscillations occur as a normal function of power transmission and distribution; they typically do not pose a threat until there is very high demand for power. If too much power is sent over these power lines, the oscillations can become unstable, akin to a teeter-totter exhibiting dangerous up-and-down swings. This instability can lead to a system breakup, causing significant disruptions of power.
New damping controller improves oscillations
According to the Sandia report, this new damping-controller technology was developed to improve the damping of these oscillations, which can enable higher power flows from one region to another. Since 1996, the primary method for mitigating inter-area oscillations is by limiting power flows through these congested transmission lines. By limiting the power flow, the occurrence of poorly damped inter-area oscillations is greatly reduced. These limited power flows result in grid congestion where the lowest-cost electricity is not able to reach customers on high-demand days, such as very hot periods during the summer months. This is uneconomical for the power providers and potentially insufficient and expensive for power customers.
Early attempts to design damping controllers in the 1970s were unsuccessful because of lack of appropriate feedback signals. Also, wide-area-measurement technology did not yet exist. The only method used was to measure local power signals for feedback, which itself led to destabilization of one of the primary inter-area oscillation modes in the Western Interconnection during an experiment. The recent development and grid implementation of phasor measurement units constitute a vast improvement that damping controllers can leverage for feedback control strategies.
The damping control system uses phasor measurement units, which allow for real-time, time-synchronized measurements to be taken from sensors installed throughout the Western Interconnection power grid. These measurements are then used to construct a feedback control signal to modulate power flow along the 850-mile Pacific DC Intertie, from northern Oregon to Los Angeles, California.
“The phasor measurement units are deployed throughout the Western Interconnection, giving the damping control system the ability to determine the necessary control input to improve the damping of any troublesome inter-area oscillatory modes, while not affecting the damping of other well-behaved inter-area oscillatory modes,” said David. “By using smart-grid technology, the damping control system will help to ensure that a stronger, safer, and more economically efficient level of power can be delivered during peak demand times.”
The damping control system is the first instance of a wide-area control system using phasor measurement units for feedback control in North America. For the development and successful grid demonstration of the new system, the project team won the R&D 100 Award in 2017. The full report, written by Sandians David, Brian Pierre, Felipe Wilches-Bernal, Ryan Elliott, and Raymond Byrne ; Jason Neely; and Daniel Trudnowski from the Montana Technological University, is available by clicking here.