Armature (electrical engineering)

In electrical engineering, an armature is the power-producing component of an electric machine. The armature can be on either the rotor (rotating part) or the stator (stationary part) of the electric machine. In electrical engineering, an armature is the power-producing component of an electric machine. The armature can be on either the rotor (rotating part) or the stator (stationary part) of the electric machine. The armature interacts with the magnetic field (magnetic flux) in the air-gap; the field component can comprise either permanent magnets, or electromagnets formed by a conducting coil, such as another armature (i.e., doubly-fed electric machine). 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 machine 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, generated power is drawn from the stator. A growler is used to check the armature for shorts, opens and grounds. The word armature was first used in its electrical sense, i.e. keeper of a magnet, in mid 19th century. The parts of an alternator or related equipment can be expressed in either mechanical terms or electrical terms. Although distinctly separate these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. This may cause confusion when working with compound machines like brushless alternators, or in conversation among people who are accustomed to work with differently configured machinery. In most generators, the field magnet is rotating, and is part of the rotor, while the armature is stationary, and is part of the stator. Both motors and generators can be built either with a stationary armature and a rotating field or a rotating armature and a stationary field. The pole piece of a permanent magnet or electromagnet and the moving, iron part of a solenoid, especially if the latter acts as a switch or relay, may also be referred to as armatures.