Written-Pole technology was no
accident.
Precise Power Corp. of Palmetto, Florida, has been working for decades to develop single-phase electric motors with low starting current requirements and high operating efficiency under load.
Two of the company’s main criteria were the elimination of phase converters and a reduction in demand charges paid by power utility customers.
The starting demand for any Written-Pole motor is only 30 percent that of a comparable single-phase or three-phase induction motor, which reduces electrical demand and voltage flicker in utility distribution systems.
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Although a Written-Pole looks like a normal electric motor on the outside, Dale Friesen of Meridium Power said the rotor is the secret to the patented technology.
“A conventional three-phase induction type motor uses a low resistance rotor,” he said.
“That’s where the Written-Pole concept is different. The engineers at Precise Power figured out how to use a high resistance rotor that impacts the initial start-up characteristics of the motor. High electrical resistance in the rotor creates higher efficiency.”
When it comes to putting heavy machinery into motion, Precise Power said its new 100 horsepower motor has a peak starting current only 1.5 times the motor’s rated full-load current, while still generating 125 percent of the motor’s rated full-load torque. It said this is sufficient torque to start nearly any load in the 100 hp range.
At the lower end of the power spectrum, the start-up requirement for a 15 hp Written-Pole is 2.1 times the total current.
“A conventional induction type electric motor typically has a start-up requirement six to eight times the operating current,” Friesen said.
“In essence, only 10 to 15 percent of the current does any useful work in startup. The rest of the current is wasted as heat and to magnetize the motor itself.”
He said Written-Pole motors converts 85 to 95 percent of the starting energy into real work.
“Our start-up current on the 15 hp is 120 amps. On a conventional 15 hp induction motor, start-up current is 350 to 400 amps. It’s a huge difference.”
Operating requirements are also lower with the Written-Pole design. The 15 hp Written-Pole is a 56 amp motor that only needs a 70-amp breaker. By comparison, a conventional 15 hp motor requires a breaker between 100 and 150 amps.
“Our 30 hp motor draws 100 amps and runs comfortably on a 125 amp breaker,” he said.
“Our new 100 hp motor draws 170 amps and runs comfortably on a 200 amp breaker. Generally, the electrical codes say that your breaker should be 150 to 250 percent of the full load rating of the motor. We’ve found that the Written-Pole single-phase motors are quite comfortable running with a breaker that is only 125 percent of the full load rating.”
The lower operating current not only reduces power bills, but also reduces motor temperature and increases motor life.
