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WAPA » Newsroom » News features » 2020

Grounding stirrup solves mulitple issues

​By Philip Reed and Kevon Storie 
Photos courtesy of Charles Kinnaird

When Electrical Engineer Gary Zevenbergen encounters problems, he puts his mind toward solving them. Sometimes he even ends up solving problems he didn’t know existed.

This was the case with a grounding stirrup he developed with Ricardo Moreno and Courtney DeFoor, two other WAPA electrical engineers. The innovative attachment turned out to have important applications beyond what he expected.

One of Zevenbergen’s responsibilities is to conduct an annual engineering study to determine the proper personal ground cable requirements for WAPA substations and transmission lines. The requirements include cable size, number of cables per phase and maximum allowable cable length.

Two key elements in determining these parameters is knowing the maximum available fault current at each work site and the ground cable’s fault-current rating. 
The ground cable parameters must be determined to ensure that the ground cable assembly will not fail should the equipment become accidently energized during maintenance. This requires using a ground cable assembly that has a fault-current rating greater than the maximum available fault current.

When the maximum available fault current exceeds the fault-current rating of the largest ground cable—a condition that exists at many locations on WAPA’s system—two, or possibly three, cables are installed in parallel. Until recently, industry standards provided little guidance on how to handle this situation. The standards indicate that it is up to the user to determine whether or not their ground cable application is adequate. Several large, investor-owned utilities have taken it upon themselves to conduct high-current testing of ground cable assemblies to determine their performance when installed as two- and three-cable arrangements.

Zevenbergen represents WAPA on several technical committees that address protective grounding issues. The technical committees are associated with Institute of Electrical and Electronics Engineers and the American Society for Testing and Materials. His participation allowed him to network with utilities performing the high-current tests and to see many of their findings. One of the most recent findings was crucial to the development of what would become the grounding stirrup.

“We learned that the clamps of two- or three-cable assemblies should be no more than three inches apart,” he explained. “If they’re next to each other, it’s fine. One inch, two inches, three inches, fine. More than three and the cable assembly will fail.”

The problem was that positioning the clamps at the correct distances from each other in a field environment would be very difficult. To Zevenbergen, the solution was clear: Create a device that would limit the distance between clamps, so that they could not be more than three inches apart.

He discussed the possibility of designing such an attachment with Moreno, but it remained an idea until a major WAPA construction project turned it into a necessity.

When the substation design work for the San Luis Transmission Project began in July 2017, it called for upgrading the circuit breakers at Tracy Substation. Tracy is a yard with high-fault current levels—exactly the kind of location where the specialized attachment would be useful. Moreno contacted Zevenbergen and they began to develop the design in earnest.

“We looked at off-the-shelf solutions, and none of them really suited our needs,” Zevenbergen said. “Either that, or they raised complications of their own. If we built our own solution, we’d know it would be exactly what we needed.”

In collaboration with equipment vendor DMC Power, which ultimately produced the device, an aluminum prototype was developed consisting of a thick base attached to a loop. The inner width of the loop was 12 inches, allowing for a maximum of three ground cables to be clamped to it without leaving a gap of more than three inches between them.

To complement this “hot-end” stirrup, which is mounted to the substation equipment, DeFoor came up with a customized “cold-end” stirrup that could be mounted near the ground where the ground cable clamps could be attached.

WAPA and DMC Power tested both stirrups at Powertech Labs and determined that the designs successfully withstood high-current levels without failure. The stirrup was proven to be a viable solution.

When Zevenbergen brought the new stirrup to Tracy Substation in April 2018, he learned that he had inadvertently solved a different, unrelated issue as well.
“We approached this to solve an engineering problem,” said Zevenbergen. “But the crew at Tracy immediately saw how it could solve an ergonomic problem.”

Foreman II Electrician Charles Kinnaird explained that the mere act of installing ground cables was often a tricky and dangerous one. He said that attaching them to conductors could be difficult, as they would need to be attached at awkward angles—sometimes even vertically. Needless to say, this was rough on the crews performing the work.

“We have experienced back and shoulder injuries installing the grounds,” said Kinnaird. “There was one instance in a high-wind situation in which an electrician had a bone in his wrist crushed. It required surgery and three months of lost work.”

With the grounding stirrup, Kinnaird and his colleagues immediately saw their solution. The thick base attached securely to conductors, and the loop provided a straight and easily accessible clamping point for ground cables.

The Tracy Substation crew tested the device, attaching it first to a spare disconnect switch in the yard and then to the bottom of a scissor lift. This allowed them to determine its ease of use when it came to attaching grounds both up close and at significant height.

“Attaching the grounds was easier and much faster,” said Zevenbergen. “Afterward I heard from an employee at another substation. She said she wished she’d known about the grounding stirrup, because she spent all day attaching grounds when she could have done it in 10 minutes with these!”

The employees at Tracy Substation wasted no time in ordering more stirrups, and they have since installed them on five breakers.

“The installation is simple and does not require too much effort to get most of the jumpers to line up with the new stirrups,” said Kinnaird.

The grounding stirrup is available for order by anyone who might benefit from using it, whether that be for engineering or ergonomic reasons.

“One thing that I hope people take from this is that they speak up when they run into problems,” said Zevenbergen. “If I had known they were having such difficulty installing grounds, I could have taken action sooner. I’m glad that I inadvertently helped them solve their problem, but I wish I had known in advance.”

Zevenbergen encourages employees, especially those in the field, to reach out when they feel there might be room for improvement.

“I’m an engineer,” he said. “Let’s engineer some solutions.”

Reed is a public affairs specialist. Storie is a technical writer under the Wyandotte contract.

Grounding stirrup
Grounding stirrup

Grounding stirrup in use
In addition to solving a safety problem
with grounding, the stirrup solved an 
ergonomic problem as well by making
it easier to attach ground cables to
conductors.
Page Last Updated: 2/10/2020 3:15 PM