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A DC armature of a miniature motor (or generator)

A partially-constructed DC armature, showing the (incomplete) windings

In electrical engineering, an armature is the component of an electric machine which carries alternating current.^[1] The armature windings conduct AC current 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 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.

Terminology[edit]

The word armature was first used in its electrical sense, i.e. keeper of a magnet, in mid 19th century.^[2]

Nov 23, 2012 In small d.c. Machines, armature slots are sometimes not made axial but are skewed. Though skewing makes winding a little more difficult, yet it results in (a) quieter operation. Brushed DC Motor Technology and History Electric motors and model trains go way back: an early motor, one of the first designed to be more than a laboratory curiosity, Davenport’s motor of 1834, was a brushed DC motor (using stator coils, not permanent magnets, so it was what modelers call a “wound field” motor).In 1835 he demonstrated it using a model train on a small circular track.

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.

Since the skewed rotor slot is not parallel to stator slot in an Induction motor, there is more leakage reactance. As a result induction motor has lower starting, maximum torques. With skewed rotor bars, the revolving flux, in effect, encounters an air gap of uniform reluctance and this results in a uniform torque and quieter operation. Rotor of an Induction Motor skewed due to following reason With the bar skewed,the amount of the bar cutting the field line grows continuously and the next bar starts cutting the field lines as the first finishes.Due to this,we get Uniform Torque. May 21, 2015 Two-layer Winding. In this type of winding, there are two conductors or coil sides per slot arranged in two layers. Usually, one side of every coil lies in the upper half of one slot and other side lies in the lower half of some other slot at a distance of approximately one pitch away (Fig.

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.^[3] 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.

Armature reaction in a DC machine[edit]

In a DC machine, 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 machines adding intermediate magnetic poles, connected in the armature circuit.

Armature reaction is essential in amplidyne rotating amplifiers.

Armature reaction drop is the effect of a magnetic field on the distribution of the flux under main poles of a generator.^[4]

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Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows in the coils. This field is at right angles to the generator field and is called cross magnetization of the armature. The effect of the armature field is to distort the generator field and shift the neutral plane. The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines, that is why an axis lying in this plane is called as magnetic neutral axis (MNA).^[5] This effect is known as armature reaction and is proportional to the current flowing in the armature coils.

The geometrical neutral axis (GNA) is the axis that bisects the angle between the centre line of adjacent poles. The magnetic neutral axis (MNA) is the axis drawn perpendicular to the mean direction of the flux passing through the centre of the armature. No e.m.f. is produced in the armature conductors along this axis because then they cut no flux.^[6] When no current is there in the armature conductors, the MNA coincides with GNA.

The brushes of a generator must be set in the neutral plane; that is, they must contact segments of the commutator that are connected to armature coils having no induced emf. If the brushes were contacting commutator segments outside the neutral plane, they would short-circuit 'live' coils and cause arcing and loss of power.

Without armature reaction, the magnetic neutral axis (MNA) would coincide with geometrical neutral axis (GNA). Armature reaction causes the neutral plane to shift in the direction of rotation, and if the brushes are in the neutral plane at no load, that is, when no armature current is flowing, they will not be in the neutral plane when arm

Why Armature Slots Are Skewed