Motor Terminology
F
Field:
A term commonly used to describe the stationary stator component of a DC Motor. The field provides the magnetic field with which the
mechanically rotating rotor component interacts.
Field Weakening:
The introduction of resistance in series with the shunt wound field of a DC
motor to reduce the voltage and current which weakens the strength of the
magnetic field and thereby increases the motor speed.
Flange:
Mounting endshield with special rabbets and bolt holes for mounting such
equipment as pumps and gear boxes to the motor or for overhanging the motor on
the driven machine.
Flux:
The magnetic field which is established around an energized conductor or
permanent magnet. The field is represented by flux lines creating a flux pattern
between opposite poles. The density of the flux lines is a measure of the
strength of the magnetic field.
Form Wound: A type of coil in which each winding is individually formed and placed into the
stator slot. A cross sectional view of the winding would be rectangular. Usually
form winding is used on high voltage, 2300 volts and above, and large motors
(449T and above). Form winding allows for better insulation on high voltage than
does random (mush) winding.
Fractional Horsepower Motor:
A motor usually built in a frame smaller than that having a continuous rating of
one horsepower, open construction, at 1700 -1800 rpm. Within NEMA frame sizes
FHP encompasses the 42, 48 and 56 frames. (In some cases the motor rating does
exceed 1 HP, but the frame size categorizes the motor as a fractional.) The
height in inches from the center of the shaft to the bottom of the base can be
calculated by dividing the frame size by 16.
Frame:
The supporting structure for the stator parts of an AC motor; in a DC motor the
frame usually forms a part of the magnetic coil. The frame also determines
mounting dimensions (see frame size).
Frame Size:
Refers to a set of physical dimensions of motors as established by NEMA. These
dimensions include critical mounting dimensions. 48 and 56 frame motors are
considered fractional horsepower sizes even though they can exceed 1 horsepower,
143T to 449T are considered integral horsepower AC motors and 5000 series and
above are called large motors.
Frequency:
The rate at which alternating current makes a complete cycle of reversals. It is
expressed in cycles per second. In the U.S. 60 cycles (Hz) is the standard while
in other countries 50 Hz (cycles) is more common.
Full Load Current:
The current flowing through the line when the motor is operating at full-load
torque and full-load speed with rated frequency and voltage applied to the motor
terminals.
Full Load Torque:
That torque of a motor necessary to produce its rated horsepower at full-load
speed, sometimes referred to as running torque.