The Cargill Oilseeds canola-crushing facility, located outside of Clavet, Saskatchewan, first opened in 1996, using a Provox DCS with Modicon PLCs for discrete I/O. Prior to its expansion in 2009, the facility migrated to DeltaV in 2008. Darren Walls, technical sales specialist at Spartan Controls in Saskatoon, Saskatchewan, worked on all of the original Provox configuration and his company was contracted to do all of the DCS work when a refinery was added in 2015.
Walls knows the controls at the Cargill plant as well as anyone does. As the facility continues to modernize and digitalize, he was part of a plan to give operators more information. Walls shared the story at this week’s Emerson Global Users Exchange in San Antonio, explaining how this plant integrated smart motor control centers (MCCs), giving operators the right information to make the plant run more efficiently.
“When a motor stops or trips, an operator should know what happened within 5 seconds,” explained Walls. “We should be able to distinguish between an electrical problem and a process interlock, so we can get the plant back up as quickly as possible.”
The original plant had Modicon PLC I/O for motor I/O. It used Emerson’s Mynah PLC I/O scanner and Virtual I/O Module (VIM) gateway to interface to the PLC drops. “A typical motor had seven inputs—control fuse, MCC disconnect, field stop, overload, output fuse, field start and run aux—and one output,” said Walls. “There was code in the PLC to send the status up to the Provox, but there was a delay in getting the statuses up.”
Spartan Controls decided to put those inputs directly in the control modules and color-code the control wiring to correspond with the MCC.
“We put the color on the faceplate,” explained Walls. “We’re telling the electricians right where to go and what the problem is. We give them the alarm for the motor, and we tell them the cause on the faceplate and the graphics. The color coding is there, and they know to go and reset. If there’s a trip on an overload at midnight, the operator is allowed to go and reset because there’s no maintenance there. If it runs, they can keep the plant running. If it trips again, they have to call maintenance staff.”
Cargill uses a balloon diagram to visualize programming. “If I’ve got low pressure, the diagram shows it’s going to interlock the pump, for example,” explained Walls. “Cargill does the programming. During a software FAT, they’ll test the interlock. They’ll do final checks when a plant is commissioned. If we’re going to add an interlock to a high tank level, you highlight the balloon diagrams, copy and reuse.”
Prior to the plant expansion, when Cargill went from Provox to DeltaV, the faceplates would pop up over the display real estate, making it cluttered. “We tried to limit the screen real estate; we have some code so if they mouse down over an ‘I’ it will bring up the interlocks,” explained Walls. “They’re allowed to put bypasses on certain pieces of equipment and certain instrumentation. There are some critical safety devices that we don’t allow them to bypass. They can bypass a transmitter, for example, so the whole plant isn’t down while it’s waiting to be replaced.”
Previously, everything was DeviceNet. “The MCCs were wired for DeviceNet,” said Walls. “We tried to keep the number down to 30 devices/segment. Each Rockwell Automation E3 Plus overload relay has four inputs—MCC, field stop, run, field start—and two outputs. We used no Rockwell software, and the electricians configured all of the devices.”
The new plant has the same input statuses and same color coding. “When a relay trips, you get an overload status, and a button comes up on the faceplate,” said Walls. “The operator can try once, and, if the button pops again, they have to get someone from maintenance. The electrician can log in via DeltaV Explorer to look at the fault code.”
In an effort to try to continue to improve, the next step will be to bring in the trip status. “The cause of the trip will come up automatically,” explained Walls. “We’re going to put that information right on the faceplates. Now, they’ll get ‘current imbalance’ or ‘phase loss,’ rather than a ‘jam’ or an ‘overload,’ so it will indicate which personnel needs to look at it for repair.”