- The rotating part of a brush-type direct current motor.
- In an induction motor, the squirrel cage rotor.
The relationship between the operating time and the resting time of an electric motor. Motor ratings according to duty are:
- Continuous duty, the operation of loads for over one hour.
- Intermittent duty, the operation during alternate periods of load and rest.
Intermittent duty is usually expressed as 5 minutes, 30 minutes or one hour.
A measure of the rate of work. 33,000 pounds lifted one foot in one minute, or 550 pounds lifted one foot in one second. Exactly 746 watts of electrical power equals one horsepower. Torque and RPM may be used in relating to the horsepower of a motor. For fractional horsepower motors, the following formula may be used.
HP = T (in.-oz) x 9.917 x N x 107
HP = horsepower
T = Torque
N = revolutions per minute
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.
The turning effort or force applied to a shaft, usually expressed in inch-pounds or inch-ounces for fractional and sub-fractional HP motors.
- Starting Torque: Force produced by a motor as it begins to turn from standstill and accelerate (sometimes called locked rotor torque).
- Full-Load Torque: The force produced by a motor running at rated full load speed at rated horsepower.
- Breakdown Torque: The maximum torque a motor will develop under increasing load conditions without an abrupt drop in speed and power. Sometimes called pull-out torque.
- 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.