AC¡ªAlternating current.
AFCS¡ªAutomatic flight control system.
ALTERNATING CURRENT (AC)¡ªAn electrical
current that constantly changes amplitude and
changes polarity at regular intervals.
AMPLITUDE¡ªThe maximum instantaneous value
of an alternating voltage or current, measured in
either the positive or negative direction.
APU¡ªAuxiliary power unit.
ARMATURE¡ªThe windings in which the output
voltage is generated in a generator or in which input
current creates a magnetic field that interacts with
the main field in a motor.
AUTOTRANSFORMER¡ªA transformer in which
the primary and secondary are connected together
in one winding. Used to step up or step down
voltages.
AUXILLARY POWER UNIT (APU)¡ªAn aircraft
mounted gas turbine power plant with an attached
generator, capable of providing electricity, engine
starting air, and air conditioning for the aircraft.
Requires only the aircraft battery and fuel for
starting.
BATTERY¡ªA device for converting chemical energy
into electrical energy.
BRUSH¡ªThe conducting material, usually a block of
carbon, bearing against a commutator or slip ring
assembly that allows current to flow in or out of a
component.
BUS¡ªSystems of like priority on a common line.
BUS BAR¡ªA primary power distribution point
connected to the main power source.
CAPACITOR¡ªTwo electrodes or sets of electrodes in
the form of plates, separated from each other by
insulating material called the dielectric, capable of
storing electrical energy in an electrostatic field.
COMMUTATOR¡ª(1) The copper segment on the
armature of a motor or generator. It is cylindrical in
shape and is used to pass power into or from the
brushes. (2) A mechanical device that reverses
armature connections in motors and generators at
the proper instant so that current continues to flow
in only one direction. In effect, the commutator
changes ac to dc.
CONSTANT SPEED DRIVE (CSD)¡ªA mechanical
unit mounted to aircraft engines which converts
variable engine speed to a constant output speed.
Generators are mounted to constant speed drives in
order to maintain the proper generator output
frequency.
CSD¡ªConstant speed drive.
CURRENT¡ªThe movement of electrons past a
reference point. The passage of electrons through a
conductor. Measured in amperes.
DC¡ªDirect current.
DIODE¡ªA material of either geranium or silicon that
is manufactured to allow current to flow in only one
direction. Diodes are used as rectifiers and
detectors.
DIRECT CURRENT (DC)¡ªAn electrical current
that flows in one direction only.
EXCITER¡ªAuxiliary dc generator.
FIELD WINDING¡ªThe coil used to provide the
magnetizing force in motors and generators.
FREQUENCY¡ªThe number of complete cycles per
second existing in any form of wave motion, such
as the number of cycles per second of an alternating
current.
GENERATOR¡ªA machine that converts mechanical
energy into electrical energy.
GPU¡ªGround power monitor.
GROUND¡ªA metallic connection with the earth to
establish ground potential. A common return to a
point of zero potential.
GTCP-95 UNIT¡ªGas turbine power plant unit, an
APU.
HERTZ (HZ)¡ªAunit of frequency equal to one cycle
per second.
HZ¡ªHertz.
AI-1
INVERTER¡ªA mechanical device that converts a dc
input to an ac output. Usually converts 26 volts dc
to 115 volts ac for an emergency source of ac power
for safety of flight systems and instrumentation.
MAGNETIC FLUX¡ªThe total number of lines of
force issuing from a pole of a magnet.
MIM¡ªMaintenance instruction manual.
NICAD BATTERY¡ªNickel-cadmium battery.
PERMANENT MAGNET GENERATOR¡ªFurnishes
control voltage and power for the voltage
regulator.
PHASE¡ªThe angular relationship between two
alternating currents or voltages when the voltage or
current is plotted as a function of time. When the
two currents or voltages are in phase, the angular
difference is zero, and both reach their peak
simultaneously. When the two currents or voltages
are out of phase, one will lead or lag the other, and
reach their peaks at different times. These
differences in may differ in polarity as well as
magnitude.
PMG¡ªPermanent magnet generator.
POWER¡ªThe rate of doing work or the rate of
expending energy. The unit of electrical power is
the watt.
PRIME MOVER¡ªA device such as aircraft engines,
gearboxes, or constant speed drives that provide the
driving force for a generator.
RECTIFIER¡ªA device used to convert ac to pulsating
dc.
RF¡ªRadio frequency.
ROTOR¡ª(1) The revolving part of a rotating electrical
machine. The rotor may be either the field or
the armature, depending on the design of the
machine. (2) The rotating member of a synchro that
consists of one or more coils of wire wound on a
laminated core. Depending on the type of synchro,
the rotor functions similarly to the primary or
secondary winding of a transformer.
RPM¡ªRevolutions per minute.
SALIENT POLE¡ªA pole consisting of a separate
radial projection having its own iron pole piece and
its own field coil, used in the field system of a
generator or motor.
SHUNT¡ªA resistive device placed in parallel with
another component. Appreciable current may flow
through it and an appreciable voltage may exist
across it.
SLAB¡ªSealed lead-acid battery.
SLIP RINGS¡ª(1) Contacts that are mounted on the
shaft of a motor or generator to which the rotor
windings are connected and against which the
brushes ride. (2) Devices for making electrical connections
between stationary and rotating contacts.
SOLENOID¡ªAn electromagnetic coil that contains a
movable plunger.
SOLID-STATE DEVICE¡ªAn electronic device that
operates by the movement of electrons within a
solid piece of semiconductor material.
STATOR¡ª(1) The stationary part of a rotating electrical
machine. The stator may be either the field or
the armature, depending on the design of the
machine. (2) The stationary member of a synchro
that consists of a cylindrical structure of slotted
laminations on which three Y-connected coils are
wound with their axes 120 degrees apart.
SYNCHRO¡ªA small motor-like analog device that
operates like a variable transformer and is used
primarily for the rapid and accurate transmission of
data among equipments and stations.
TACHOMETER¡ª(1) A small ac or dc generator,
sometimes referred to as a rate generator, that
converts its shaft speed into an electrical output.
The tachometer is frequently used in servo systems
to sense the velocity of a load. (2) An instrument
that measures the rate at which a shaft is turning.
TORQUE¡ªThe turning effort or twist that a shaft
sustains when transmitting power. A force tending
to cause rotational motion; the product of the force
applied times the distance from the force to the axis
of rotation.
TR¡ªTransformer-rectifier.
TRANSFORMER¡ªA device composed of two or
more coils, linked by magnetic lines of force, used
to transfer energy from one circuit to another.
VLAB¡ªVented lead-acid battery.
VOLT¡ªThe unit of electromotive force or electrical
pressure. One volt is the pressure required to send 1
ampere of current through a resistance of 1 ohm.
WYE(Y)¡ªAthree phase connection in which one end
of each phase winding is connected to a common
ground.
ZENER DIODE¡ªA PN-junction diode designed to
operate in the reverse-bias breakdown region.
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