The high cost of installing three-phase electrical service to rural areas, whether for irrigation pumps or grain-handling motors, may not be as necessary as commonly thought thanks to the maturing of an electrical-engineering concept developed over the past 25 years.
So-called written-pole electric motors, developed by Precise Power of Bradenton, Fla., in the late 1990s, are unique in their ability to provide up to 100-plus horsepower ratings on single-phase utility power. That alone makes them an attractive alternative as a prime mover in remote settings, because single-phase power is widely available throughout North America — whereas installing three-phase power can cost $20,000-$100,000 per mile in lightly-populated areas.
Written pole motors are equipped with a layer of permanent ferrite magnets encased in ceramic on the surface of the rotor — a design that allows those magnets to be “written” by microprocessors either positive or negative as needed depending upon the load and rotor speed. The design was tested extensively in Canada in 2000 and proved its ability to start at less than two times its running current rating. A 30 horsepower prototype drew only 1.7 times its rated running current load in those tests.
Typically, a traditional induction motor can draw 6-12 times its rated running current draw when starting from a dead stop. That peak starting current is a load demand utility companies must account for in their generating capacity, and a demand for which they charge consumers dearly. Lighter starting loads also reduce dimmed-lights and low-voltage dips for neighbors on the grid when such motors come online.
Another efficiency written-pole motors bring to the equation is their ability to run at what engineers call “unity power” — a condition in which current and voltage requirements change in step. In conventional induction motors, current and voltage are frequently not synchronized at operating speed, which causes a “reactive load” to the power supplier — another condition that triggers extra “power-factor” charges.
Precise Power and now Single-Phase Power Solutions LLC (SPPS), which recently purchased manufacturing rights from PP to manufacture written-pole motors in its facilities in Cincinnati, Ohio, has hundreds of these motors in operation in the oil patch and on farms and material-handling facilities across the U.S. and Canada, all providing low-maintenance, easy-starting, reduced-cost power through their inherent design efficiency.
SPPS produces the Belle Written-Pole motor in sizes ranging from 30-100 horsepower.
Marketing Manager Ben Morris says the company’s engineers are working on larger models since the technology is scalable.
Recently, however, irrigators and some grain handling operations have adopted an innovation being promoted by SPPS, which involves using a 100 horsepower single-phase Belle motor to drive a three-phase generator. The 1-to-3 Power Source operates on 208, 240 or 480 VAC and can power enough three-phase motors to equal its own 100 horsepower rating.
The 3-to-1 Power Source also includes a 600 pound flywheel between the motor and the generator to even out any power fluctuations that might occur on the grid.
In the High Plains of west Texas, irrigators have been bypassing high three-phase utility costs for more than a decade by running remote diesel-fueled or natural gas three-phase generator sets to power pumps feeding their center-pivot sprinkler systems. In many cases, SPPS’s 1-to-3 Power Source can offer those growers a savings of nearly 50% in fuel by using the Written-Pole motor’s efficiency and ability to tap existing and competitively-priced single-phase utility power.
Morris says at operating speed the motor’s efficiency is 95.5% and the generator’s efficiency is 93.5% for an overall efficiency rating of 89% — with 100% electrical isolation from the grid for the load.
Reciprocating internal-combustion engines struggle to achieve efficiency ratings much over 50% in most applications.
“Unlike conventional phase-converters, the 1-to-3 provides true balanced three-phase power, eliminates disruptive harmonic feedback on the grid, and with the added flywheel, can ride through momentary power interruptions with ease,” he says.
Harold Grall, a Dumas, Texas, corn producer is running one of the 1-to-3 Power Source units to power a 60 horsepower submersible irrigation pump, and says after a year of operation he’s pleased with the operation of the equipment.
“There’s essentially no maintenance, it’s quiet and I’m sure we could be running more of a load on it,” he explains. “They are expensive, however, so we’re going to evaluate our operating costs to see if we can, indeed, run it cheaper than burning natural gas in pumping engines or to generate our own power.
“We think we can,” he adds.
