A stator is the static part of rotary electromagnetic devices such as electric motors, alternators, and generators. It represents one of the two primary components of the device, the other being the moving rotor that supplies the working output. Depending on the device design, the stator may act as the armature or the field winding of the particular device. In either case, it remains stationary at all times while the rotor spins either around or within it.
Rotary electromagnetic machines such as electric motors and generators all consist of two basic components that, depending on the specific design in question, fulfill one of two critical functions. The two basic components are a rotating rotor and a stationary stator. In the case of a motor, the rotor is the part of the device which supplies the working motion the machine is designed to produce. In alternators and generators, the rotor is the element to which the working movement of an outside power source is applied as is seen in an automobile alternator. In both cases, the stator remains static in relation to the rotating rotor at all times during operation.
Whether the relevant machine is a motion output device such as a motor, or a source of electrical power output such as a generator, the stator and rotor fulfill one of two basic functions in the work cycle. The first is that of a field device, or field coil as it is often called. This part of the machine supplies a strong magnetic field courtesy of either a permanent magnet array or a electric coil. The function of the second element in the work cycle is that of an armature. This is the part of the machine with which the magnetic field interacts to provide the output of the device.
In many devices, both parts may fulfill either the role of field device or armature. For instance, a large industrial motor will feature the field coil located within the static outer stator component with the armature being represented by a laminated steel core surrounding the rotor which turns within the stator. A small brushless direct current (DC) motor driving a computer cooling fan, on the other hand, will have the field coil wound around a centrally-located stator. The rotor component will, in contrast to the previous example, revolve around the outside of the static component. In both cases, though, the stator is always the static element in the machine.