Wireless Protection Communications—Innovating to Improve Reliability

But to make this smart grid program work, AES Ohio would have to solve a new challenge: coordinating the protective functions of not just one or two, but many recloser controls on the same circuit.

When recloser controls are properly coordinated within the protection scheme and FLISR goes into action, an outage that previously would have affected every customer on a line could now affect as few as a couple hundred. But recloser miscoordinations would cut power to longer line sections than necessary, undercutting their reliability goal.

The utility’s engineering analysis concluded that 40 percent of its recloser controls would be susceptible to miscoordination. This often becomes an issue when reclosers are located in close proximity; multiple recloser controls are likely to detect the same level of fault current and, with no other way to tell which one is actually closest to the fault, several could trip at once.

To coordinate the protective actions of its close-proximity recloser controls and achieve the full benefits of its smart grid program, AES Ohio would need to use high-speed communications. 

Although the company had fiber-optic communications in many substations, its sprawling distribution circuits had no fiber infrastructure. And it had neither the resources nor the time to undertake such a large capital project.

Meanwhile, the product development team at SEL, knowing that many utilities lack the resources to install fiber-optic infrastructure, had been working on an innovative, cost-effective option for protection communications—a wireless system that could transmit the fault status to other devices at protection speed.

The system consists of three interlocking components: an SEL-FT50 Fault Transmitter, an SEL-RP50 Fault Repeater, and an SEL-FR12 Fault Receiver.

The compact SEL-FR12 Fault Receiver is installed in a cabinet alongside a protective relay or recloser control and plugged into the communications port of the protective device. The SEL-FT50 Fault Transmitter is mounted directly on an overhead power cable; when it detects fault current, it broadcasts the fault status via 900 MHz wireless signals to an SEL-FR12 either directly or via up to five line-mounted SEL-RP50 repeaters. In typical conditions, it takes only 6 milliseconds to send fault data to the protective device, with each repeater in the communications chain adding just 1.5 milliseconds of delay to the overall latency.

But the thing about innovation, as SEL R&D engineer Anthony Rahiminejad makes clear, is that it involves a leap of faith. “Nobody asked us to develop this product. There were no customers lined up for this when we started. The reason we did it is because we were looking forward and saw a need for it.”

AES Ohio was looking forward as well.

And when its engineers asked SEL Application Engineer Chris Burger if he had heard of any products that could help them solve their recloser coordination dilemma, he knew just the thing: the recently released SEL Wireless Protection System, the only product of its kind on the market.

“We haven’t come across anything that isn’t fiber that works this fast,” says AES Ohio Lead Protection Engineer Dan Dull.

The SEL Wireless Protection System had the speed they needed to make protection coordination possible—so AES Ohio collaborated with SEL to set up a pilot installation on a distribution circuit and evaluate the system.

Rahiminejad visited Ohio to provide training on using the new product—and returned to SEL with information that the R&D team used to further refine it. Burger worked closely with the AES Ohio pilot project team as they hung the fault transmitters and repeaters on the line, set up each SEL-FR12 Fault Receiver in its recloser cabinet, and adjusted the protection settings in each recloser control.

The pilot installation was a success. AES Ohio now had not only proof that the solution would work, but also, thanks to Burger’s collaboration, a ready-to-order configuration of the SEL-651R-2 Advanced Recloser Control with an SEL-FR12 Fault Receiver preinstalled in the cabinet.

Dull describes how the installation process typically goes now that the system is being deployed at scale. Having chosen settings for the recloser controls and the wireless communications system based on the characteristics of the distribution circuit they’re going into, he then creates a detailed report specifying where the devices are to be installed, along with other essential information for the installation crews.

Dull typically uses reference materials to make an educated guess at how many repeaters might be needed. But, he adds, “it’s awful hard to tell what you need in the field just by looking at an aerial or satellite view.”

Fortunately, installation crews are able to adjust on the fly; the SEL-RP50 is easy enough to set up that it doesn’t have to be programmed in advance. Line crews can just stop when they see the signal has attenuated to a certain point, program the settings into a repeater on the spot, and hang it on the line with a hot stick.

“One thing I really like about the solution,” says Zachary Sharp, who was a supervising test engineer during the pilot installation, “is ease of use and installation. The technicians can go out in the field and engineer an ad hoc solution based on the conditions that they’re seeing.”