Written-pole Revolution

ented more than a century ago, lectric motors pervade society torunning things as diverse as factory production lines and bed-side alarm clocks. Collectively, these motors consume more than two-thirds of the electricity produced annually in the United States, with those over 5 hp (only 2 percent of all electric motors) accounting for more than 70 percent of the consumption. While these larger motors have certainly increased our nation’s productivity in applications ranging from irrigation to steel manufacturing, their conventional design has presented some challenges. One fundamental problem is that the motors require a very high current to start up, typically six to ten times the current needed to maintain full-speed operation. For rural power customers with single-phase electric service, this means not being able to run motors over 16 hp without using expensive phase converters. For large industrial customers with three-phase service, it means the potential for power quality problems like voltage dips as large motors are brought online. In the early 1980s, Precise Power Corporation, with EPRI support, developed a breakthrough technology to address these issues. Called Written-PoleTM technology, this patented approach uses innovations in magnetism to reduce a motor’s need for a high starting current. In fact, a Written-Pole motor (WPM) typically requires a starting current that is less than twice its running current. Additional advantages are the motor’s very high efficiency (92 percent in comparison with 85 percent for conventional motors) and its ability to ride through power interruptions of up to about 15 seconds. Also, WPMs can be combined with Written-Pole generators to offer an uninterruptible power source that’s not dependent on maintenance-intensive batteries. According to Precise Power, Written-Pole technology is the most significant development in motors in the past 30 years. many benefits of these devices are good for good for us,” says Dale Friesen of Manitoba Hydro, one of the utilities working most actively with Precise Power on the motors. In presenting the WPM a 1997 New Product Award, the National Society of Professional Engineers praised “its innovative use of engineering principles and materi-