Single Phase Motors

single-phase2Written-Pole® Single Phase Motors offer a revolutionary method for powering large horsepower applications in locations where only single-phase power is available.
The Written-Pole® motor is a hybrid concept, which utilizes basic concepts from induction, hysterisis and permanent magnet motors, with several important distinctions.
The primary feature which differentiates Written-Pole® single-phase motors from more conventional designs is a continuous layer of ferrite magnets on the surface of the rotor, along with a high-density exciter winding contained within the stator winding. This unique design matches the pole structure of the rotor to the rotational speed of the motor. The result is a motor that combines the desirable starting characteristics of a high-slip, high-power factor cage motor with the energy-efficient operation of an AC permanent magnet motor– without relying on power electronics, reduced voltage starters or phase converters.


The result is a powerful motor with:

Low starting current
The Written-Pole® motor starts on as little as three times or less rated current. This eliminates voltage sag interfering with other customers.

High horsepower
Conventional single-phase motors are normally rated at 15 hp or less. The Written-Pole® motor is available in sizes from 30 to 75 hp. The motor is powerful enough to replace internal combustion engines or even costly extension of three-phase service.

High efficiency
Unlike most conventional single-phase motors, the Written-Pole® motor has high efficiency – 92-95% and high power factor compared to 85% for conventional motors.

Enhanced reliability
The Written-Pole® motor is simply designed and robustly constructed. It can be expected to provide years of dependable service, even under demanding environmental conditions.

Benefits of Written-Pole® Single-Phase Motors

The following summary provides an overview of benefits of Written-Pole® single-phase motors. Based on Written-Pole® technology, a patented concept developed by Precise Power Corporation, these innovative single-phase motors offer many advantages over conventional single or three-phase electric motors.

1) Low Starting Current requirements
The most significant characteristic of V single-phase motors is their low inherent starting current. Written-Pole® single-phase motors exhibit starting current requirements ranging from 1.7 to 3 times their rated current, unlike conventional induction motors (single or three-phase) that have typical starting currents ranging from 6 to 9 times their rated current. A typical Written-Pole® single-phase motor has a starting current, comparable to a conventional single-phase motor one-fourth its rating, dramatically increasing the maximum rating that may be started on rural single-phase distribution systems.

The low starting current of Written-Pole® single-phase motors is a by-product of their unique design that combines the starting characteristics of a permanent magnet hysteresis motor (the surface of the rotor is covered with a continuous layer of ferrite magnet material) with those of a high slip, high power factor, NEMA Design D induction motor (the rotor contains a high resistance induction cage that uses steel rotor bars and end-rings to increase the electrical resistance of the rotor under starting). Upon reaching 75 to 80% of its rated speed, an excitation coil in the stator winding is energized (using AC power at line frequency), creating a strong alternating magnetic field that tailors the magnetic pole configuration of the ferrite layers for optimum starting torque and acceleration. The excitation coil is de-energized when rated speed is attained allowing the motor to operate as an energy efficient, synchronous permanent magnet motor.

Since s Written-Pole® single-phase motor’s low starting current is attained without reduced voltage starting, the design does not sacrifice starting torque as is common with three-phase motors started using reduced voltage devices designed to limit starting current. Not only does this simplify the design and construction of the motor, but it also enhances the usability of Written-Pole® single-phase motors under a variety of applications.

2) Energy Efficient Operation
The synchronous mode of operation under which Written-Pole® single-phase motors operate allows for very high operating efficiencies, comparable to those of premium efficiency three-phase motors with similar ratings. The resulting reductions in transformer loading and operating costs can represent a significant advantage over comparable installations using three-[phase motors and phase converters.

The high operating efficiency of a V single-phase motor is made possible by the fact that its synchronous mode of operation eliminated losses commonly associated with the slip in conventional induction motors. By eliminating the resulting rotor losses, Written-Pole® single-phase motors are able to substantially reduced total losses, improving operating efficiency.

3) Unity Power Factor Operation
The Synchronous mode of operation also results in near unity power factor operation at rated load (slightly leading at part load) further reducing transformer and distribution line loading. The following table illustrated the comparable operating efficiency and power factor of a Written-Pole® single-phase motor with conventional single and three-phase induction motors.

Rating (hp) 30 30
Voltage 230 208
Speed (rpm) 1800 1765
Full Load Amps 104 70
Starting Amps 197 445
Efficiency (rated load) 93.6% 93.6%
Power factor (rated load) Unity 0.85
Input Power (rated load) 23.9 kW 23.9 kW
Input kVA (rated load) 23.9 kVA 28.1 kVA
Input kVA (starting) 45.3 kVA 160.3 kVA