Hawaiian Electric exec receives patent on device to stabilize wind energy on small or remote grids

HONOLULU, Hawaii, July 20, 2004 — Dr. Karl E. Stahlkopf, Hawaiian Electric Company senior vice president for energy solutions and chief technology officer, has received a patent for an “electronic shock absorber” designed to increase the prospects of wind energy in Hawaii and around the world.

“If successful, the electronic shock absorber will stabilize a wind farm’s energy fluctuations. The better frequency and voltage control of the transmission system will increase wind generation in Hawaii,” Stahlkopf said. “The device should be applicable to island systems around the world as well as to weaker transmission systems on the mainland.”

Working with a team of engineers from HECO and Hawaii Electric Light Company (HELCO), Stahlkopf came up with a plan to insert an electrical energy storage system, a control system, and an electronic compensation module between the wind farm and power transmission line.

Stahlkopf was inspired to invent the device during a visit to the HELCO operations center
in Hilo when he saw the impact of fluctuating wind energy on the Big Island’s power grid.
The patent approval for the electronic shock absorber (ESA) idea came through more quickly than he had expected, Stahlkopf said. The next step will be to build a prototype of the design.

Stahlkopf joined HECO in 2002, coming from the Electrical Power Research Institute in
Palo Alto, California where he was vice president of the power delivery after a nearly 30 year career with the power industry’s leading “think tank.” He has a B.S. degree in Electrical Engineering and a BS in Naval Science from the University of Wisconsin in Madison, an MS and Ph.D. degrees in Nuclear Engineering from the University of California, Berkeley. A national magazine for electrical engineers recently described his job as one of the 10 “coolest, baddest, hippest, grooviest and most gratifying” in electrical engineering.

The Power Quality Products Division of S&C Electric Company, a global provider of equipment and services for electric power systems, is working with HECO on the prototype and any follow-on systems. Chicago-based S&C was founded in 1911 and has successfully served the electric utility and industrial market since that time with innovative protection and switching equipment.

If successful, the ESA will make it easier to add clean, efficient renewable wind energy to Hawaii’s electric production. To reduce the use of imported fossil fuel, Hawaii recently enacted a law that sets a target for renewable energy at 10 percent by 2010, 15 percent by 2015 and 20 percent by 2020. Last year, 8.4 percent of the energy sold by HECO and sister companies HELCO and Maui Electric Company came from renewable sources.

Wind has long been regarded as one of the most promising potential renewable energy resources for Hawaii. With the Hawaii Department of Business, Economic Development and Tourism’s energy division, HECO last year published new wind resource maps showing the places across the islands with the greatest potential to support wind generation.

Why is the ESA needed? Electrical systems must balance production of electricity with customer demand. The measure of this balance is frequency (the cycling rate of alternate current electricity), which is 60 Hertz (Hz) when the production exactly matches demand. If production is greater than customer demand (plus power losses) frequency will be greater than 60 Hz. If production is less than the customer demand (plus losses), frequency is less than 60.

A system with changes in frequency is not stable, and if frequency goes too high or too low the system can have problems — from loss of service to some customers cascading all the way to an island-wide blackout. Because wind ebbs and flows from moment to moment, a wind farm can inject instabilities in a relatively small transmission system (such as for an isolated region or island).

Conversely, fluctuations in the grid can also affect a power source. Transient conditions such as temporary power outages or flashovers on a transmission line can cause a power source’s safety circuitry to automatically disconnect it from the grid. A re-closer or other relay device would be needed to reconnect the power source to the grid once the transient condition has passed.

For small-contributor power sources, such as a wind farm, the addition of a re-closer or relay device adds considerable additional cost to the system. For small power systems, such as an island grid, or a weakly supported interconnected grid where the wind farm represents a major generation source (above 5% of total power), if the wind farm is unable to immediately reconnect to the grid after the fault is cleared there may be enough imbalance to cause the entire grid to shut down due to under frequency.

The ESA which Stahlkopf has invented is able to store excess power during periods of increased generation and release stored energy during periods of decreased generation due to wind fluctuations. The control system is provided with a “look ahead” capability for predicting wind-speed conditions and power output. This data and system-modeling algorithms are used to predict and maintain energy storage or release despite short duration fluctuations.

The power control interface can also use its energy storage capacity to provide voltage support at the point of injection into the power transmission system, as well as fault clearance capability for “riding out” transient fault conditions occurring on the power transmission line. The ESA system can thus increase the overall capacity factor of the wind farm’s contribution to the grid, provide voltage support at the point of injection, and improve overall transmission system stability.

The electronic shock absorber can also enable a wind farm to help reinforce the transmission system, i.e., provide voltage support, against power problems originating elsewhere on the transmission system.

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