The definition of the armature
In electrical engineering, an armature is the component of an electric motor which carries alternating Current. The armature windings conduct AC even on DC machines, due to the commutator action (which periodically reverses Current direction) or due to electronic commutation, as in brushless DC motors. The armature can be on either the rotor (rotating part) or the stator (stationary part), depending on the type of electric machine.
The armature windings interact with the magnetic field (magnetic flux) in the air-gap; the magnetic field is generated either by permanent magnets or electromagnets formed by a conducting coil.
The armature must carry Current, so it is always a conductor or a conductive coil, oriented normal to both the field and to the direction of motion, Torque (rotating machine), or force (linear machine). The armature’s role is twofold. The first is to carry Current across the field, thus creating shaft Torque in a rotating machine or force in a linear machine. The second role is to generate an electromotive force (EMF).
In the armature, an electromotive force is created by the relative motion of the armature and the field. When the machine or motor is used as a motor, this EMF opposes the armature Current, and the armature converts electrical power to mechanical power in the form of Torque and transfers it via the shaft. When the motor is used as a generator, the armature EMF drives the armature Current, and the shaft’s movement is converted to electrical power. In an induction generator, the generated power is drawn from the stator.
A growler is used to check the armature for short and open circuits and leakages to the ground.
Armature reaction in a DC motor
In a DC motor, two sources of magnetic fluxes are present: armature flux and main field flux. The effect of armature flux on the main field flux is called “armature reaction”. The armature reaction changes the distribution of the magnetic field, which affects the operation of the machine. The effects of the armature flux can be offset by adding a compensating winding to the main poles, or in some motors adding intermediate magnetic poles connected in the armature circuit.
In a “lap” winding, there are as many Current paths between the brush (or line) connections as there are poles in the field winding. In a “wave” winding, there are only two paths, and there are as many coils in series as half the number of poles. So, for a given rating of the machine, a wave winding is more suitable for large Currents and low Voltages.