Power Engineering | ECE | Virginia Tech


Power Engineering

Twilight photograph of wind turbines

While demand increases for alternative energy sources, research is needed to understand how to integrate them into the power grid, according to Bradley Fellow Keith McKenzie, who is investigating the interaction of wind energy sources with the power grid.

McKenzie is developing models that accommodate the multiple wind turbine topologies and associated power electronics that interface to the grid. A key issue being investigated involves energy storage configurations and whether, given advance warning of a power grid disturbance, the wind turbine/energy storage system can dampen some of the resulting oscillations.

He is also studying how to prevent wind turbine energy sources from negatively impacting the grid. For example, wind gusts can lead to active power fluctuations, causing voltage fluctuations in a weak grid. Another issue involves the low voltage ride-through capability of a wind turbine. A wind turbine will disconnect when the voltage dips below a given value. If the dip is caused by a nearby fault in the system, the disconnection of the turbine can create a second disturbance that leads to a cascade-effect of multiple wind turbines disconnecting.

Virginia Tech power engineers have been working with researchers from Arizona State University on a multi-year project to investigate methods of improving the security of electric power supply systems. The project has been funded under a $300,000 grant from the NSF.

"Innovations in computer-based monitoring, protection, and control of electric power supply systems, coupled with the availability of wide-band high-speed communications have made it possible to bring about the development of very highly secure electric supply networks," said Arun Phadke, the principal investigator on the project.

The project involves a multidisciplinary team of students and faculty members in the fields of power engineering, communications systems, and new sensor developments.

The team is also studying the social and economic impact of electric supply systems, with a goal of developing a metric to measure the societal and economic dependence on electricity supply and the cost of insecurity of the system.

Virginia Tech's frequency monitoring network (FNET), which is the first installed system to monitor the entire U.S. power grid, is providing data for a number of different investigations ranging from security, to system disturbance location.

FNET uses low-cost sensors, developed at Tech, that are plugged into standard 120V outlets at various university and office locations nationwide. Since the units do not need to be installed at substations, FNET provides an independent observation system of the U.S. power grids. Other monitoring systems are typically confined within the operational boundaries of their utilities.

To date, more than 30 units have been installed around the country and are relaying continuous data via the internet. Bradley Fellow Robert Gardner is on the team of researchers tapping the raw frequency data and developing useful applications.

Gardner's work focuses on frequency data analysis and conditioning, power-system event detection, and power system event location. Early results from data conditioning are helping the team understand the nature of power system frequency, he says. His future work in the area will focus on understanding more about the probability distribution of frequency data from different parts of the country.

He has also been on a team to develop an oscillation analysis tool to serve as an inter-area power-flow-oscillation warning device. The tool complements others the FNET team has developed, such as generator trips and load rejections to detect and classify power system events.

Another key area is researching power system event location. Events with magnitudes greater than 300 MW disperse frequency perturbations throughout the grid. The waves are detected by FNET and the team is working on tools so that disturbances can be detected without respect to utility boundaries.

"Using the results of this research, operators in system A can understand and react to a disturbance caused by neighboring system B without having to instrument their neighbor's system," he said. "If such capabilities had existed in August of 2003, the Northeastern Blackout that left New York City in the dark could have been reduced or mitigated completely."

Print Version

image of article

(96KB .pdf)
Print Version