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​By Lisa Meiman

In early December 2018, employees energized WAPA’s first-ever variable shunt reactors in two northern California substations to alleviate and stabilize potentially damaging voltage conditions along sections of Sierra Nevada’s 230-kilovolt lines.

“Shunt reactors mitigate high voltages,” said Foreman III Electrician Jim Higgins. “If load is too light, the voltage can creep up. Fines can be imposed if the voltage gets too high for too long.”

The variable shunt reactors were energized in Elverta Substation Dec. 4 and Olinda Substation Dec. 6 to absorb excess reactive power and improve control of long-distance transmission line voltage, particularly overnight.

“We’re seeing some immediate impact from them,” said Higgins. “Initially, we didn’t know how the variable shunt reactors were reacting in the system because generators can compensate as well. When we looked at equipment reports, we found out Elverta’s reactor was fully engaged.”

The project began about six years ago when SN examined how to resolve high voltages during light loading conditions, or light demand, without relying on the area’s generation sources.

High voltages can damage equipment and create grid instability. The historical solution was to use local generation sources as voltage control. Over time, that practice became more challenging as generating units retired and renewable distributed generation increased, which can result in high-voltage conditions during off-peak hours. New regulations also played a role.

“SN’s 230-kV system has always had voltage problems, but now we are more accountable to mitigate them,” said Higgins. “We must take more ownership.”

In 2013, a team concluded that variable shunt reactors would provide SN the best voltage control instead of the fixed ones WAPA has traditionally installed across its transmission system.

Unlike the fixed reactor, the variable reactor uses a baseline value and a range to regulate increases or decreases in voltage based on actual system conditions.

“Variable shunt reactors allow for incremental voltage regulation,” Higgins said. “Fixed shunt reactors are all or nothing.”

Variable reactors could also meet the requirements with about half the space of fixed shunt reactors. If SN had decided to go with fixed reactors, they would have needed to purchase, install, operate and maintain twice as many reactors.

Construction began in August 2017 and was completed as scheduled in March 2018 at about $4 million under the estimated $12 million cost.

“Smooth construction was possible due to better planning for equipment supplies, flexibility, dedication from our craft and engineers and good work quality of the construction contractor,” said Project Manager Zia Islam.

After construction was complete, various WAPA employees completed several rounds of testing before the project could be safely energized.

“There are three steps after construction: testing, commissioning and energizing,” said Islam. “Electrical and maintenance engineers evaluate the equipment against a protective scheme to make sure everything is working properly.”

Because many SN electricians had never worked with variable shunt reactors before, new training was required.

“It’s always exciting to get new equipment that you haven’t worked with before,” said Higgins. “The units themselves are unique. They are similar to traditional reactors but not exactly the same, so we had to get familiar with the nuances.”

“Overall, the project went pretty well,” said Islam. “We were able to maintain the schedule and kept it under budget.”

Note: Meiman is a public affairs specialist.

Variable shunt reactor

WAPA’s first-ever variable shunt reactors were energized at the end of 2018. 

(Photo by Jim Higgins)

Last modified on March 8th, 2024