Three-Phase Conversions Gain Traction for Grain Dryers

Father and son both wondered late last year why they hadn't done it sooner: installed three-phase motors with phase converters on their single-phase service.

"I don't understand the science, but the converter changes the phase of the electricity coming in to allow us to use a three-phase motor," says Tyler Wynthein of Arlington, Iowa, who farms with his father, David.

They now run two large motors that would not have been feasible to run on single phase before. They aren't the only ones doing it. John Molumby, customer relations manager for the Allamakee-Clayton Electric Cooperative (ACREC) in northeast Iowa, says Wynthein's reaction is typical, and he's seeing it frequently.

"Typically, people wish they had done it a lot sooner. Usually the price scares them at first. Once they make the change, they wish they had done three phase long ago," Molumby says.

Three-phase availability should be a prime consideration for any operation that needs motors with more than 10 hp., Molumby says. "You don't have to live where your grain dryer is. You can turn them on and monitor them from home."

three-phase availability key to decision

If three phase is reasonably close, Molumby says getting a new dryer and some financial help through the USDA's REAP program makes going with three phase affordable. When three-phase power happens to be available at the farm gate, Molumby says ACREC charges $4,600 to "get the three tubs [capacitors] and build the line into them." If it isn't at the gate, the base rate for three phase is about $80,000 per mile since it requires heavier poles and closer pole spacing.

The utility offers revenue consideration to bring the cost down. Factors include age and reconstruction plans for the single-phase service line and level of usage. For instance, a new dairy has a very different usage profile (and better revenue consideration) than a grain farm with seasonal needs, which may be only four weeks in a year. When costs for full three-phase service on a grain farm are excessive, the utility, electricians, and system installers start talking about phase converters, soft starts, or variable-frequency drives (VFD).

employing a combination of converters

ACREC also has electronic and rotary phase converters. "A lot of members go with a combination of the two or a rotary type, depending on how many motors they're looking at. There are two types of phase converters: rotary and electronic.

• Rotary is like putting another motor out there to pick up two more phases. You lose some efficiency when you do that.
• Electronic does a little better conversion because you trick the motor into thinking it's picking up the other phases.

In the 1980s, solid-state electronics led to development of variable-frequency drives that enable this approach to operate three-phase motors with single-phase supply lines. Programmable circuitry first made VFD technology affordable in the 1990s for factories and industry.

Also known as inverters and adjustable-speed drives, they work by converting the supply voltage to direct current (DC) and then convert the DC to a suitable three-phase source for the motor.

The VFD has three subsystems that include an alternating current (AC) motor, which is usually a three-phase induction motor; a solid-state programmable controller; and an interface so you can start, stop, and adjust the system.

Motor controls specialist Brian Koehler of Washington, Iowa, designs, programs, and installs phase conversion systems as a major part of his Powercom company business. He launched the company in 2005. It serves Iowa farmers directly and farms in other states through its website.

Today, Koehler says a farm VFD installation can slash annual electric bills, giving a quick payback on the investment. "It's getting really popular now for farms," he says.

A typical VFD installation

The subject comes up when established farms need a big motor or a power upgrade and when new sites need heavy motors. A typical VFD installation is built inside a 24×24×8-inch electrical box and is mounted beside whatever motor it controls. Single phase comes in, three phase goes out.

Three-phase motors are the only option when farm electrical needs exceed the capacity of the largest single-phase 10-hp. motors, Koehler says.

For the same horsepower, three-phase motors are less expensive to buy than a single phase. They are more economical to operate, less troublesome, and need less maintenance. Depending on the size of the system, the front-cost differences can be thousands of dollars.

For motors, VFD is all about easing the transition between start and stop. It provides precise speed and torque control, giving the motor a slow (or soft) start.

Companies like Powercom use programming and memory chips to tame that surge so neighbors never notice.

VFD used in new grain site

Koehler employed VFDs to solve power issues for Lonnie Burgmaier and his son, Jeromy, at Creston, Iowa, in 2007. The Burgmaiers had started plans for a new 8-acre storage and drying site. It needed motors with up to 75-hp. capacity. When Koehler learned that only single-phase service was available to the farm, he asked Powercom for help.

Koehler built the base system in 2007, then he expanded it in 2010. The site now has four 50,000-bushel bins and one 200,000-bushel bin. Koehler used VFD to operate a 75-hp. three-phase motor that runs the fan for the grain dryer. Three 40-hp. motors with VFD units run the ventilation fans on the big bin, and there are four 15-hp. motors for the smaller bins. The Burgmaiers also use three-phase motors on two horizontal conveyors and two grain legs above the bins.

"We burn a lot of propane with it, but we do not dim the neighbors' lights when we start that 75-hp. motor, even though it's on single phase. That's the nice thing about soft start," Lonnie Burgmaier says. "It's adjustable, so we start that big motor slowly."

Since the original installation, the Burgmaiers say the system has been trouble-free.