When Mark Robinson talks about cleanliness, he means something entirely different than most of his fellow workers do at Minneapolis-based General Mills Inc. As the electrical and controls engineer at the food producer’s plant in Cedar Rapids, Iowa, his job is to worry about the cleanliness of the facility’s electrical power. When “dirty” power polluted with momentary sags and interruptions finds its way into the automation, it can turn the electronics off and shut the plant down without warning.

Although recovery for some processes is as simple as turning the machinery back on, it is much more complex for the production of some cereals. Recovery there entails both cleaning the equipment and leading the process through a start-up phase until it reaches steady state. Not only do these electrical failures waste material and cost the company in lost production, but they also can damage expensive electronics.

These sags, as well as surges, can come unexpectedly from a variety of sources, such as failing capacitors and damage caused by storms. “Most of these blips are of short duration because relays in the system usually detect and isolate faults within five to 10 cycles,” notes Robinson. “They are long enough to shut the entire line down, though.”

Such shutdowns tend to occur more frequently these days because electronics have become more sensitive to changes in power quality. “Voltage sags and brief interruptions are by far the most expensive power problem for most industrial automation users in the developed world,” reports Dr. Bill Brumsickle, vice president of engineering at SoftSwitching Technologies Corp., of Middleton, Wis.  “But damaging voltage deviations do not leave evidence behind them—often, the lights will not even blink.”

Even though people may not see any evidence of sags as they occur, the equipment can feel them acutely. The symptoms are seemingly random stoppages in production and premature failures in the electronics. These expenses have been escalating to the point where a growing number of facilities are recognizing power quality as a problem and are investing in technology that can “cleanse” their electricity.

At the General Mills plant in Cedar Rapids, the initial cleansing process included installing capacitors and replacing components that would go offline easily during a sag. With this level of protection, “we could handle a sag down to about 80 percent without any processes going down in the plant, as long as it didn’t last too long,” says Robinson.

Yet, there continued to be about eight sags a year that were significant enough to shut down portions of the plant and wreak havoc in cereal production. Because a large number of these sags occurred during storms, the initial plan for dealing with them was to do what the plant was already doing for its critical utilities. It called for installing an expensive set of diesel generators and switching all aspects of cereal production onto them whenever the radar in the boiler room detected an approaching storm.

Robinson put the plan on hold, however, when he discovered a cheaper and more effective technology, SoftSwitching’s DySC Dynamic Voltage Sag Corrector. During a short voltage sag in three-phase power, the device uses internal inverter and cross-coupler technology to borrow power from the unaffected phases to boost voltage in the affected one. It also can draw from capacitors whenever a sag affects all three phases, thereby freeing the user from dependence upon batteries.

Cheaper, yet effective

According to its manufacturer, the sag corrector is also efficient, consuming less than 1 percent of the energy in the application, which makes it 99 percent efficient. “To reduce susceptibility to common voltage sags, some facilities have ‘tapped up’ their internal distribution voltages by as much as 5 percent, which increases system losses by as much as 10 percent,” says Brumsickle. “In such cases, installing a DySC and returning to nominal voltage levels can reduce energy usage by over 5 percent.”

General Mills installed the sag correctors at Cedar Rapids. Rather than backing up the entire cereal plant with large-capacity units, much like was proposed in the diesel-generation plan, Robinson opted instead for a less-costly solution. He put only the control systems on 13 smaller correctors, one for each unit operation. During a power sag, the correctors regenerate the wave to the sensors, instrumentation, input/output (I/O), probes and the other components in the control system. The exception is the programmable logic controllers (PLCs), which had already been connected earlier to an uninterruptible power supply (UPS).

Because motors are not connected to the correctors either, they start ...