armature (electrical engineering) - wikipedia, the free encyclopedia

8/2/2019 Armature (Electrical Engineering) - Wikipedia, The Free Encyclopedia

1/3

5/04/2012 Armature (electrical engineering) - Wikipedia, the free encyclopedia

.wikipedia.org/wiki/Armature_(electrical_engineering)#Armature_reaction_in_a_DC_machine

A DC armature.

Armature (electrical engineering)From Wikipedia, the free encyclopedia

In electrical engineering, an armature generally refers to one of the two

principal electrical components of an electromechanical machine

generally in a motor or generator, but it may also mean the pole piece of

a permanent magnet or electromagnet, or the moving iron part of a

solenoid or relay. The other component is the field winding or fieldmagnet. The role of the "field" component is simply to create a magnetic

field (magnetic flux) for the armature to interact with, so this component

can comprise either permanent magnets, or electromagnets formed by a

conducting coil. The armature, in contrast, 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 crossing 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 is acting as a motor, this EMF opposes the armature current, and the armature converts electrical power mechanical torque, and power, unless the machine is stalled, and transfers it to the load via the shaft. When the

machine is acting as a generator, the armature EMF drives the armature current, and shaft mechanical power is

converted to electrical power and transferred to the load. In an induction generator, these distinctions are blurred,

since the generated power is drawn from the stator, which would normally be considered the field.

A growler is used to check the armature for shorts, opens and grounds.

Contents

1 Terminology

2 Armature reaction in a DC machine

3 Winding materials

4 See also

5 References

6 External links

Terminology

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 such as brushless alternators, or in conversation among people who are accustomed to work with

differently configured machinery.

In alternating current machines, the armature is usually stationary, and is known as the stator winding. In DC

rotating machines other than brushless DC machines, it is usually rotating, and is known as the rotor. The pole piec


2/3



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.

echanical

Rotor: The rotating part of an alternator, generator, dynamo or motor.

Stator: The stationary part of an alternator, generator, dynamo or motor

Electrical

Armature: The power-producing component of an alternator, generator, dynamo or motor. The armature can beon either the rotor or the stator.

Field: The magnetic field component of an alternator, generator, dynamo or motor. The field can be on either the

rotor or the stator and can be either an electromagnet or a permanent magnet.

Armature reaction in a DC machine

In a DC machine, the main field is produced by field coils. In both the generating and motoring modes, the armatu

carries current and a magnetic field is established, which is called the armature flux. The effect of armature flux on

the main field is called the armature reaction.

The armature reaction:

1. demagnetizes the main field, and

2. cross magnetizes the main field.

The demagnetizing effect can be overcome by adding extra ampere-turns on the main field. The cross magnetizing

effect can be reduced by having common poles.

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.[1]

Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows i

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 positio

where the armature windings are moving parallel to the magnetic flux lines. This effect is known as armature reactio

and is proportional to the current flowing in the armature coils.

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.

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 armature

current is flowing. For this reason it is desirable to incorporate a corrective system into the generator design.

These are two principal methods by which the effect of armature reaction is overcome. The first method is to shift

the position of the brushes so that they are in the neutral plane when the generator is producing its normal load

current. in the other method, special field poles, called interpoles, are installed in the generator to counteract the


3/3



effect of armature reaction.

The brush-setting method is satisfactory in installations in which the generator operates under a fairly constant load

If the load varies to a marked degree, the neutral plane will shift proportionately, and the brushes will not be in the

correct position at all times. The brush-setting method is the most common means of correcting for armature

reaction in small generators (those producing approximately 1000 W or less). Larger generators require the use of

interpoles.

Winding materials

The electrical energy efficiency of a motor can be improved by reducing the electrical losses in the coil (e.g., by

using materials with higher electrical conductivities). Armature wiring is made from copper or aluminum. Copper

armature wiring enhances electrical efficiencies due to its higher electrical conductivity (See: Copper in energy

efficient motors). Aluminum armature wiring is lighter and less expensive than copper.

See also

Balancing machineCommutator

Electric generator

References

1. ^ A.Van Valkenburgh (1993).Basic Electricity (http://books.google.com/books?

vid=ISBN0790610418&id=vmg1UKsTntAC&pg=PT666&lpg=PT666&ots=BpGdNz1lT0&dq=Armature+Reaction

+Drop&ie=ISO-8859-1&output=html&sig=UPP07UxX3VLD3nmIZxUexDnnZ9A) . Thomson Delmar Learning.

ISBN 0790610418. http://books.google.com/books?

vid=ISBN0790610418&id=vmg1UKsTntAC&pg=PT666&lpg=PT666&ots=BpGdNz1lT0&dq=Armature+Reaction+Drop&ie=ISO-8859-1&output=html&sig=UPP07UxX3VLD3nmIZxUexDnnZ9A.

External links

Example Diagram of an Armature Coil and data used to specify armature coil parameters

(http://www.swigercoil.com/upload/newsletter/dcarmature.pdf)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Armature_(electrical_engineering)&oldid=483567708"

Categories: Electromagnetic components Electric motors

This page was last modified on 23 March 2012 at 18:43.

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply.

See Terms of use for details.

Wikipedia is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.

armature (electrical engineering) - wikipedia, the free encyclopedia

Documents