Page 59 - Electrical Engineering Dictionary

point between the higher (ω H ) and lower maximum allowable limit due to excessive
(ω L ) band edges, expressed in units of ra- heating of the stator.
dians/second. The band edges are usually
defined as the highest and lowest frequencies armature reaction (1) in DC machines, a
within a contiguous band of interest at which distortion of the field flux caused by the flux
the loss equals L Amax , the maximum attenu- created by the armature current. Armature
ation loss across the band. reaction in a DC machine causes lower flux
at one pole-tip and higher flux at the other,
ω H + ω L
ω oa = which may lead to magnetic saturation. It
2
also shifts the neutral axis, causing sparking
on the commutator.
arithmetic shift a shift in which it is as-
(2) in AC synchronous machines, a volt-
sumed that the data being shifted is integer
age “drop” caused by the armature current.
arithmetic in nature; as a result, the sign bit
In the steady state model of the synchronous
is not shifted, thereby maintaining the arith-
machine, the armature reaction is accounted
metic sign of the shifted result. See also
for by a component of the synchronous reac-
logical shift.
tance.
arithmetic–logic unit See arithmetic and
armature voltage control a method of
logic unit.
controlling the speed of a DC motor by vary-
ing the voltage applied to the armature while
arm apartofarobot. Arobotiscomposed
keeping the voltage applied to the field circuit
of an arm (or mainframe) and a wrist plus
constant.
a tool. For many industrial robots the arm
subassembly can move with three degrees of
armature winding an arrangement of
freedom. Hence, the arm subassembly is the
coils carrying the main current, typically
positioning mechanism. See also industrial
wound on the stator of a synchronous ma-
robot.
chine or the rotor of a DC machine, in which
an alternating voltage is induced by the mag-
arm pin a pin insulator .
netic field.
ARMA See auto-regressive moving-aver-
age model. armless construction a method of distri-
bution line construction, often used for aes-
armature the magnetic circuit of a ro- thetic purposes, in which pin insulators are
tating electrical machine, including the main mounted on steel brackets bolted directly to
current carrying winding, in which an alter- a utility pole without the use of a crossarm.
nating voltage is induced by the magnetic
field. Armstrong oscillator Hartley oscillators
are usually not used at VHF of higher fre-
armature circuit components of the ma- quencies. Similarly, the circuit is avoided at
chine that carry armature current. For ex- very low audio frequencies. It is important
ample, in a DC machine the armature cir- to distinguish the Hartley oscillator from the
cuit could consist of the armature windings, Armstrong topology. In the Armstrong oscil-
brushes, series field winding, compensat- lator, no ohmic connection exists between the
ing windings, interpoles, starting resistor(s), two inductors. Instead, coupling is entirely
main-line contacts, and overload sensor. magnetic.

armature current limiting a condition Armstrong, Edwin Howard (1890–
wherein the stator currents are clamped at the 1954) Born: New York, New York, U.S.A.

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2000 by CRC Press LLC