LEESON Electric Corporation  

Glossary of Terms

The number of individual voltages applied to an AC motor. A single-phase motor has one voltage in the shape of a sine wave applied to it. A three-phase motor has three individual voltages applied to it. The three phases are at 120 degrees with respect to each other so that peaks of voltage occur at even time intervals to balance the power received and delivered by the motor throughout its 360 degrees of rotation.
A method of braking a motor that involves applying partial or full voltage in reverse to bring the motor to zero speed.
As applied to electric circuits, polarity indicates which terminal is positive and which is negative. As applied to magnets, it indicates which pole is north and which pole is south.
Magnetic devices set up inside the motor by the placement and connection of the windings. Divide the number of poles into 7200 to determine the motor’s normal speed. For example, 7200 divided by 2 poles equals 3600 RPM.
Power Factor:
The ratio of “apparent power” (expressed in kVA) and true or “real power” (expressed in kW).
Power Factor = Real Power/ Apparent Power
Apparent power is calculated by a formula involving the “real power,” that which is supplied by the power system to actually turn the motor, and “reactive power,” which is used strictly to develop a magnetic field within the motor. Electric utilities prefer power factors as close to 100% as possible, and sometimes charge penalties for power factors below 90%. Power factor is often improved or “corrected” using capacitors. Power factor does not necessarily relate to motor efficiency, but is a component of total energy consumption.
Prime Mover:
In industry, the prime mover is most often an electric motor. Occasionally engines, hydraulic or air motors are used. Special application considerations are called for when other than an electric motor is the prime mover.
Pull Out Torque:
Also called breakdown torque or maximum torque, this is the maximum torque a motor can deliver without stalling.
Pull Up Torque:
The minimum torque delivered by a motor between zero and the rated RPM, equal to the maximum load a motor can accelerate to rated RPM.
Pulse Width Modulation:
Abbreviated PWM, the most common frequency synthesizing system in AC drives; also used in some DC drives for voltage control.
General Info
Metric IEC