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Energy efficiency supports automation upgrades

Automation upgrades to older equipment in U.S. manufacturing plants are a familiar story, but not as much in the food and beverage industry. The industry has felt the effects of a record number of mergers and acquisitions (M&A), and proceeded to move forward with large automation projects to scale efficiencies.

However, small food companies are still searching and implementing their own modernization projects for better reliability and efficiencies. One example is the Minn-Dak (Minnesota-Dakota) Farmers Cooperative and the recent update of its drive motor system for processing sugar beets.

The cooperative uses Siemens Sinamics S120-CM drive technology to implement a common DC bus solution to optimize energy consumption for this multi-step process operation. This upgrade also includes Simiatic S7-1200 PLC controllers and fourteen integrated inputs/outputs. 

Minn-Dak processes sugar beets and their sweet conical roots, which includes washing, slicing, boiling and drying. One of the last steps at its Wahpeton, N.D. plant is to remove excess moisture before it gets turned into sugar.

To do this, the plant uses six large centrifuges to spin juice from processed beets and separate usable sugar crystals from the remaining material. During each cycle, the centrifuges process 2,000 lbs. of juice and sugar crystals, also known as massecuite. Each centrifuge has a corresponding motor and they endure large acceleration and deceleration phases during these three-minute cycles.

“The centrifuges are set to prescribed speeds for a specific amount of time and then back to zero,” says Bob Jacobson, GM at Malloy Electric, which integrated the automation components for the Minn-Dak plant.  “At the beginning of each cycle, an operator will empty 800 pounds of sugar and this means each centrifuge will run through this cycle approximately 700 times in each 24-hour period.”

With such large volumes in this critical drying stage, reliability took front and center with the recent equipment upgrade.

“If the centrifuges don’t run, we don’t produce,” says Merlyn Mindeman, I&E supervisor at Minn-Dak. “First, we considered a single drive per centrifuge solution but we decided on a common bus solution—the same kind of approach we had been using with the older equipment.

The Siemens S120 common bus system design includes two active front ends that can provide power and can go to all six motors. The active front end—the other end is redundant—changes 480V AC to DC power to run the S120 motor modules and will put power back on the AC power line, if a motor slows too quickly, according to Malloy Electric.

“This quick slowing turns the motor into a generator and would cause DC bus voltage to rise, and then the S120 controller to trip over voltage,” says Jacobson. 

With this common DC bus design, regenerative power is used by the other S120 driver controllers and ultimately consume less power from the AC source.

“If they can’t use all of the regenerative power, the active front end will change to AC power and put it on the electrical grid,” says Jacobson. The drive controller has this functionality built in and is simply set up when this is commissioned.”

For Minn-Dak’s common DC bus operation, a full load on 300 HP motor is 329 amps and all six motors could draw as much as 2000 amps, fully utilized.

After installation of the new drive controls, the total amp draw ranges from 50 to 550 amps with all six centrifuges running, according to Malloy Electric.

As with most automation updates in today’s food production plant, better energy data visibility is on the plant floor. Minn-Dak is now able to monitor motor operation, such as error codes, along with amps and drive alarms via Human Machine Interface (HMI) panels.