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Cellular-based SCADA shines during Hurricane Charley
Many water and wastewater operators have implemented private wireless telemetry supervisory control and data acquisition (SCADA) systems to monitor and control their pumps, valves and lift stations.
They believed the high level of performance and reliability required dictated that they “roll their own,” and not depend on other services. In 2004, several communities in Hurricane Charley’s path found out that cellular-based data transmission not only is up to the task but also outperforms traditional methods and costs less.
Digital cellular-based SCADA systems are rapidly gaining acceptance in the water and wastewater utility industry. Hundreds of systems are now deployed and many others are testing the new technology. Unlike the older “cellular voice auto dialers,” the new cellular SCADA systems utilize control channel cellular data services, or third-generation (3G) cellular data services, to transmit telemetry to and from pumping stations, lift stations and field instrumentation sites.
While attracting many customers because of their ease of use and low costs, customers wonder how the systems will stand up during a natural disaster. Will the data still get through when everyone is trying to make cellular phone calls?
Put to the test
In August 2004, Hurricane Charley came ashore on the southwest coast of Florida and tore a path diagonally through the state. In Charley’s path were numerous utilities with cellular SCADA units deployed.
Hillsborough County Utilities serves the Tampa Bay area, and has been testing control channel and 3G cellular SCADA units for some time. An evacuation of the coastal area was ordered, because Charley was predicted to make a direct hit. Mission Communications was in contact with Hillsborough County employees preparing for the worst.
“Mission was helping the customer rearrange their alarm callout list and turn off certain alarms so as to not swam the field personnel with unnecessary calls during the storm,” said John Collings, president of Mission Communications. “One of the advantages of the system is that data can be accessed securely from almost anywhere and suppliers can help administer a customer’s system during extraordinary events such as this.”
One of the Hillsborough units is located at the intersection of two major highways near the Tampa International Airport. This remote terminal unit (RTU) transmits site level and pump status continuously. Throughout the evacuation, the two local highways near the site were jammed.
Even with the thousands of ongoing cellular phone calls being served near the site, Mission recorded not one delay or data disconnect. The real-time data units send data as pumps turn on and off and as wet well levels rise and fall.
“You can literally watch what is happening at a pump station real-time,” said Collings. “This particular pump station is extremely active due to its shallow well and high flow. Frankly, we would have anticipated a few reconnects due to its high data transmit rate and the proximity to the highway, but it performed flawlessly.”
Capacity and redundancy
The latest cellular-SCADA units transmit tiny amounts of data compared with an ongoing voice conversation. The cellular system fills in the millisecond gaps in voice conversations with data from field units. If there is even a short delay of voice data, the caller will experience garbled voice or a dropped call. With packetized data, a slowdown is an inconvenience but the data still moves through the system. Because a cellular system is designed for voice, where each call transmits thousands of bytes per second, telemetry sent at a rate of tens of bytes per minute can easily find spare capacity. Also, because most locations are covered by multiple cell sites, if a site goes down the radio automatically tunes to the frequencies used by another nearby tower and the connection continues as if nothing had happened. In a voice call this is analogous to a car driving out of the coverage area of one cell into the coverage area of the next. Handoffs like this happen flawlessly billions of times a day.
Cellular response in an emergency
Cellular carriers are keenly aware that during, and after, catastrophic events, many emergency services depend on their networks for vital, even life-saving communications. When disasters such as Charley occur, the carriers are ready to respond quickly with the full strength that a nationwide cellular carrier can muster. Most carriers have regional emergency response crews with portable generators, mobile towers, and other system-restore equipment on standby at all times. This is similar to water utilities assisting other utilities with their standby generators or bypass pumps. When a disaster can be forecast, such as a hurricane, these crews move portable, temporary cell sites called COWs (cellular on wheels) or COLTs (cellular on light trucks) to staging areas in preparation for the event. As soon as the storm has passed, this equipment can be quickly moved into affected areas to provide service and add capacity.
Taking a direct hit
Though still months from their scheduled roll-out of cellular SCADA units, Charlotte County Utilities had cellular SCADA units of both types deployed in the Port Charlotte, Fla., area. The units transmitted power failure messages just before 5 p.m. During the passage of the eye, the 3G cellular units began reconnecting and some reconnects took as long as 11 minutes.
At 5:20 and 5:24 p.m. Mission “pinged” one of the control channel cellular units for status data. The units answered back on both occasions.
For the next six hours, Charley moved through Florida. Though there were numerous temporary outages, all systems returned to normal by midnight and survived the storm.
The success of these cellular SCADA systems was summed up by Robert Bolten of Vero Beach Florida Utilities.
“There’s no way anyone could afford to build and operate a private wireless network to the standards that the likes of Cingular, Nextel, Sprint and Verizon can,” said Bolten.
“Now that these types of services are available why should they? Not to mention that a cellular SCADA system is less expensive to own and operate than any traditional SCADA system that we’ve seen. Let them do what they do best, and we will do what we do best, operate a water utility. It works better and is one less problem we have to deal with.”
Mission’s Collings added, “While we are extremely pleased with the network’s performance through this devastating storm, we have learned we need to equip units in hurricane-prone areas with five-day batteries instead of two-days, and to be thankful they don’t occur more often.”