Purpose of the BESS

During the engineering design, various devices were evaluated to provide 140 megawatts to Fairbanks as required by the Legislative grant funded portion of the Northern Intertie.

Reactive Supply

In 1994, GVEA evaluated twelve options to determine if the required delivery target could be met. Most of the options used classical reactive compensation which would provide power to maintain the voltage under the required power transfer. The BESS provides this reactive power and allows for the required power to be transferred while maintaining voltage on the Fairbanks end of the Northern Intertie. This reactive supply was the initial reason for the BESS application. If GVEA had not selected the BESS, another device would have been installed to provide the transfer.

Secure Transfer

Reactive capability of the BESS would not have justified the extra expense. As the system studies progressed, the secure transfer of 140 megawatts to Fairbanks was investigated. The existing transmission line from Healy to Gold Hill, the western side of Fairbanks, was rated and operating at 100 megawatt levels since the installation of the transmission line from Healy to Anchorage. The new Northern Intertie, from Healy to Wilson Substation, in South Fairbanks, could also be operated at 100 megawatts. As designed, the Healy to Gold Hill and the Healy to Wilson transmission lines would be operated in parallel to reduce losses and increase reliability. If both transmission lines were operated at their capacity the total delivered power to Fairbanks would be 200 megawatts.

If either transmission line were to have a problem causing them to be taken out of service, the total power flowing from Healy to Fairbanks would be transferred to the remaining transmission line. This would effectively place 200 megawatts on a transmission line that is rated for 100 megawatts and the resulting overload would require the second line to be taken out of service or risk damaging the remaining transmission line.

The BESS can provide real power in addition to the reactive supply we mentioned above. Looking at the above example with 140 megawatts of power flowing from Healy to Fairbanks and with a 40 megawatt BESS in place, the result is much different. If one transmission line is taken out of service with a 140 megawatt transfer, the BESS will supply 40 megawatts of power in Fairbanks and the remaining transmission line would be loaded within its rating of 100 megawatts, and power between Healy and Fairbanks is not disrupted. This is the main reason for the BESS as the application requires the delivery of real power from the BESS, where most other options could not provide the real power to meet the required transfer limit of 140 megawatts.

Large Fairbanks Generator Tripping (Overload of the Anchorage to Healy Intertie)

The real power from the BESS increases the stability of the system. If a large generator such as a North Pole turbine trips off line, the transmission line can become overloaded causing a wide-spread outage or blackout in the Fairbanks area. With BESS, the loss of a large generator looks like a small turbine because the BESS provides real power to replace most of the power lost with minimal, if any, outages and increasing the system reliability.

Small Fairbanks Generators or Anchorage Generator Tripping (Spinning Reserves)

Golden Valley shares in the extra generation that is running (spinning reserves) on the system in case a generator trips off line. Before the BESS, Golden Valley used to remove or shed load as our contribution to the spinning reserve requirement. This would cause numerous and very irritating short outages that would require resetting of clocks to stop the blinking 12:00.

When a generator trips off line the BESS will automatically increase its output to keep the lights on and completely eliminate the short outages by providing spinning reserves. Once the BESS is providing power into the system, other Golden Valley generation is started to back down the BESS power and reduce the discharging of the battery banks.

This benefit of the BESS is not the reason the BESS was installed, but is the one that most of our members are familiar with as it has eliminated over 1.2 million member outages in its few years plus of operation.