‘Crop Circle’ Mystery Solved With Connectivity Upgrade

asdEndless acres of radial irrigation systems gain new load-balancing benefits with utility’s new SCADA and RUGGEDCOM deployments.

Airline passengers flying above rural northeastern Nebraska are often intrigued by an endless array of green crop circles. They are fields irrigated by center-pivot systems with radial sprinkler arms, typically a quarter-mile-long pipe that can take three days to rotate full circle.

In Nebraska’s Cuming County, water is drawn from the huge Ogallala Aquifer by pumps powered by the Cuming County Public Power District (CCPPD).

Irrigation operations make up most of the CCPPD’s 300 commercial customers. The farms’ irrigation demands grid peak in the summer growing season, when electricity is subject to a load-balancing program.

“Of course, it depends on rainfall,” says CCPPD General Manager Elwood Moore. “The less there is, the more they must water. And the more we have to manage the load on our grid.”

Managing that grid in hot summers, when demand for air conditioning and irrigation are high, isn’t easy. CCPPD offers discounted rates to irrigation customers who take part in its load-control program. Using SCADA telemetry through 12 remote substations, it monitors the power drawn by their systems and turns the systems off when their loads exceed pre-set limits. “A typical load in the summer is about 25 megawatts,” Moore says. “With our load-control program, we try to dial it back to about 70 percent of that.”

The CCPPD buys its electricity from the Nebraska Public Power District. Like many utilities, the NNPD uses a progressive rate schedule to encourage conservation.

“When heavier loads force us into higher-cost rates, it raises our power bill and those of our irrigation customers,” Moore says. “It can increase their bills by as much as $2,500 a year.”

Latencies in gathering data from remote substations forced CCPPD to overcompensate in balancing its grid loads, impacting customers and costs. Its low-bandwidth wireless SCADA system suffered latencies as long as 45 minutes.

“We couldn’t see real-time loads,” says Technology Supervisor Monte Draper. “We’d have to poll all of our substations to see what the loads are, then shut off enough irrigation wells to reach our pre-determined levels. Some guesswork was always involved, and we’d over-correct to play it safe. But this meant shutting down some wells unnecessarily and for longer than needed.”

Draper adds that the load-balancing process required a CCPPD employee to take hours each day to oversee the SCADA system’s pre- and post-polling of the irrigation systems and substation load, then do manual calculations. With only eight linemen out in the field, this was a considerable staff burden. Another problem: the CCPPD’s aging SCADA system faced a forced shutdown because the system’s software vendor ended support for CCPPD’s system.

About this time, the U.S. government started its existing Smart Grid Investment Grant program. It provided funds to cover half the costs of projects that helped modernize the nation’s electric grid. Upgrading the CCPPD’s SCADA system certainly qualified, so they joined neighboring utility with similar requirements and jointly won funding.

CCPPD turned to the Siemens RUGGEDCOM Professional Services team, which helped the district conduct a comprehensive site survey and an RF propagation study. These investigations helped their RF-channel planning and system design, which ultimately helped facilitate the implementation of both the physical network and the RUGGEDCOM Network Management System (NMS).

The backbone of the CCPPD system architecture is a redundant microwave backhaul ring on five 90-foot towers with throughputs of up to 200 Mbit/s. It’s linked to each CCPPD substation and the main office data center by a Siemens RUGGEDCOM RX1500 series integrated Layer 2 and Layer 3 switch and router.

IEEE 802.16e WiMAX Siemens RUGGEDCOM WIN 7237 outdoor wireless base stations are connected to the RX1500. The CCPPD uses the 3.65 GHz radio frequency, communicating with substations as far away as 13 miles.

To deal with the line-of-sight issues of low-lying substations, the CCPPD installed repeater systems using RUGGEDCOM WIN 5237 subscriber units on the receiving end (interconnected with a WIN 7237 base station via a RUGGEDCOM RS900, a 9-port, Layer 2, fully managed Ethernet switch).

Each substation also has one of these subscriber units, along with a RUGGEDCOM RSG2100 19-port, fully managed fast/gigabit Ethernet switch to interconnect all the substation’s various IEDs. For those devices needing copper connections, the CCPPD installed a RUGGEDCOM RMC40, a 4-port unmanaged Ethernet switch with up to 100 Mbit/s speeds. The rugged Siemens network has survived three major hail storms and a pair of tornados.

“We chose Siemens RUGGEDCOM components because we knew all of its gear is utility-grade and up to the harsh outdoor conditions we have here in rural Nebraska,” Moore says. “The reliability and durability of RUGGEDCOM products is designed and built-in, not added on.”

Safety is paramount for linemen. Reducing truck rolls by using the networks gives CCPPD linemen fewer reasons to work on energized lines. “If we can do resets, reconfigurations and troubleshooting from here in the office, they’re not put in harm’s way,” he says. “But if they do need to replace a unit, we can switch our breakers on that particular circuit to one-shot status. Then the RUGGEDCOM’s easy plug-and-play installation means a lineman can do it in just a few minutes.”

In the future, Moore and Draper envision many other services they could operate over the Siemens RUGGEDCOM WiMAX network’s ample bandwidth. One example is having a Wi-Fi hotspot at each substation to give linemen and technicians information and communication access. Another is video surveillance.

“Frankly, we have just scratched the surface of what we can do with this system,” Moore says.

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