AI-1
APPENDIX I
GLOSSARY
AMPLIDYNE—A special dc generator in which a small dc voltage applied to field windings controls a
large output voltage from the generator. In effect, an amplidyne is a rotary amplifier, oftentimes
producing gain in the order of 10,000.
ARMATURE—The 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. Note: Armature is often
used as being identical with ROTOR. This usage is correct only part of the time. See the text and the
entries under ROTOR and STATOR in this Glossary.
ARMATURE LOSSES—Copper losses, eddy current losses, hysteresis losses which act to decrease the
efficiency of armatures.
ARMATURE REACTION—The effect, in a dc generator, of current in the annature creating a magnetic
field that distorts the main field and causing a shift in the neutral plane.
BRUSHES—Sliding contacts, usually carbon, that make electrical connection to the rotating part of a
motor or generator.
COMMUTATION—The act of a commutator in converting generator output from an ac voltage to a dc
voltage.
COMMUTATOR—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.
COMPENSATING WINDINGS—Windings embedded in slots in pole pieces, connected in series with
the armature, whose magnetic field opposes the armature field and cancels armature reaction.
COMPOUND-WOUND MOTORS AND GENERATORS—Machines that have a series field in
addition to a shunt field. Such machines have characteristics of both series- and shunt-wound
machines.
CAPACITOR-START MOTOR—A type of single-phase, ac induction motor in which a starting
winding and a capacitor are placed in series to start the motor. The values of Xc and R are such that
the main-winding and starting-winding currents are nearly 90 degrees apart, and starting torque is
produced as in a two-phase motor.
COUNTER EMF—The voltage generated within a coil by a moving magnetic field cutting across the
coil itself. This voltage is in opposition (counter) to the moving field that created it. Counter emf is
present in every motor, generator, transformer, or other inductance winding, whenever an alternating
current flows.
DELTA—A 3-phase connection in which windings are connected end-to-end, forming a closed loop that
resembles the Greek letter Delta. A separate phase wire is then connected to each of the three
junctions.
