Page 218 - Electrical Engineering Dictionary

handling when used in conjunction with a dy- direct axis (d axis) the magnetic axis of
namic beam control circuit. the rotor field winding of a synchronous ma-
chine. The axis between the poles of a DC
diode laser laser in which the amplifi- machine.
cation takes place in an electrically pumped
semiconducting medium. Also known as a direct axis magnetizing (armature) reac-
semiconductor laser or a heterojunction laser. tance a reactance that represents all the
inductive effects of the d-axis stator current
diode rectifier a circuit in which the out- of a synchronous machine, except for that
put voltage is fixed by the circuit parameters due to the stator winding leakage reactance.
and the load. The direction of power flow is In Park’s d-axis equivalent circuit of the syn-
not reversible. An example of a single-phase chronous machine, this reactance is the only
diode-bridge rectifier with a capacitor filter element through which both the stator and
is shown. Note that the diodes are on only rotor currents flow. Its value may be deter-
for a short duration, while the rectified line mined by subtracting the stator winding leak-
voltage is greater than the capacitor voltage. age reactance from the steady-state value of
the d-axis operational impedance or from the
dioptric an optical system made up of geometric and material data of the machine.
only refractive elements (lenses).
direct axis synchronous reactance the
dip See sag.
sum of the stator winding leakage reactance
and the direct-axis magnetizing (armature)
DIP See dual in-line package.
reactance of a synchronous machine. This
represents the balanced steady-state value of
DIP switch set of micro-switches (on/off
the direct-axis operational impedance of the
or deviators) that are compliant with the DIP
synchronous machine, and thus characterizes
for the position of their pin (connections);
the equivalent reactance of the machine dur-
thus, they can be installed in standard sockets
ing steady-state operation.
for integrated circuits.
direct axis transient reactance a value
dipole See magnetic dipole.
that characterizes the equivalent reactance
of the d-axis windings of the synchronous
dipole antenna a straight wire, with two
machine between the initial time following
arms, of oppositely pulsating charges, typi-
a system disturbance (subtransient interval)
cally λ/2or λ/4.
and the steady state. This reactance can-
Dirac’s delta function not actually a not be directly mathematically related to the
function, Dirac’s delta function is defined d-axis operational impedance. However, in
functionally by its property of “choosing” a models in which the rotor windings are rep-
single value of the integrand when integrated: resented as lumped parameter circuits, the d-
axis transient reactance is expressed in closed
Z
f(r 0 ) = f(r)δ(r − r 0 )dr form as the sum of the stator winding leak-
age reactance, and the parallel combination
when the volume of integration includes the of the d-axis magnetizing reactance and the
point r 0 . See delta function. field winding leakage reactance.

direct addressing address of the operand direct broadcast satellite (DBS) refers
(data upon which the instruction operates) of to TV signal transmission and distribution
the instruction is included as part of the in- from a base station up to a satellite, and then
struction. down to consumers who have suitable satel-

c
2000 by CRC Press LLC