Final Flashcards
diodes are ___ sensitive, they conduct in one direction only.
polarity
list several applications for diodes
any electronic device
A _____ diode can be used as an oscillator or an amplifier.
tunnel
a diode that is voltage sensitive and acts as a variable capacitor is called a _____.
varactor
when a silicon diode is installed correctly it does not begin to conduct until about 0.7 volts is applied across the diode. Why?
Surface Barrier Voltage
what happens if the PRV rating of a diode is exceeding?
destroy the diode
diodes designed to operate at the PRV rating are called _____ diodes.
zener
with a 60 hz line frequency applied to a full wave rectifier, the output ripple frequency is ____ Hz.
120 Hz
define a generator
electromagnetic device that changes mechanical energy into electrical energy.
what is the primary difference between a simple DC generator and a simple AC generator?
AC has slip rings
DC has a commutator
AC generators operate on the principle of ____
electromagnetic induction
there are two basic types of alternators. These are the revolving ____ type and the revolving ____ type
armature, field
slip rings, unlike the commutator are constructed as a _____ ring, with each end of the armature loop connected to a seperate ____
continuous, ring
what limits the amount of power that can be generated with the revolving armature type of generator?
slip rings and brushes
when the armature is held stationery in a generator, it is called the ____.
stater
what is the advantage of using a rotating field and a stationery armature on commercial generators?
You can hard wire it.
two types of rotating field construction are the ___ rotor, and the ____ rotor.
salent pole, non salent pole
the ____ is the rotating member of a generator or motor.
rotor
exciters are made in a variety of ways including ___ and ____.
fixed and rotating
pole faces that jut out and are very pronounced are called ____ poles.
salent
large capacity generators are often enclosed in a _____ atmosphere for cooling purposes.
hydrogen
formula for frequency of an alternator
of poles / 120 = FREQUENCY
what 3 factors determine the output voltage of an alternator
- strength of magnetic field
- # of loops of wire
- speed of cutting action
how do you know when the 2 alternators are in phase with each other ?
lights go out
what 3 conditions must be met when connecting two, three-phase alternators in parallel?
- same phase rotation
- A,B,C phase in same time sequence
- voltage output the same
what is the generic name for synthetic coolants?
askarel
in general, once a transformer is installed , it must be ____, to qualified persons for maintenance and repair, while access is ____ to unqualified persons
accessible, restricted
6 steps you can take to prevent the noise of a transformer from interfering with normal activities.
- select one that is quiet
- install it far away from people
- do not locate it in the corner of the room
- mount it so that its vibration is not transmitted to the structural parts of the building
- solidly mount it to the floor or concrete walls
- flexible couplings between the troughs and conduits reduce noise transfer
Ephase = Eline (Voltage) , what type of system?
Delta
Iphase = Iline (Current) , what type of system?
Wye
High means it is connected how?
in series
Low means it is connected how?
in parallel
ways to cool a transformer
- naturally air cooled
- oil cooled
- force cooled by fan
- oil cooled with water jackets
things that reduce efficiency in transformers
- heat loss
- hystoresis
- core saturation
- eddy currents
- flux linkage
it is easier to transform ___ voltage
AC
what is the heat formula
P=I2R
most electrical power today is 3 phase power, T or F
true
dc generators operate on the principle of ______
magnetic induction
what happens when a conductor cuts magnetic flux line?
a voltage is induced
what components make up the DC armature?
iron core
commutator
windings
what are the three types of armature windings found in generators?
lap wound
wave wound
frogleg
what three factors determine the level of the output voltage of a series generator?
strength of magnetic field
number of loops of wire
speed of rotation
self excited shunt generators make use of _____ to start the generation process.
residual magnetism
the greatest generation loss is due to the _____ of the armature
resistance
_____ loss is due to molecular friction
hystoresis
what might happen if two DC generators are simply connected in parallel?
they could explode
describe the physical construction of a simple power transformer.
two sets of windings wrapped around a common iron core.
a step up transformer is one which has a _____ primary voltage
lower
primary bushings are marked with the letter
H
secondary bushings are marked with the letter
X
what is the purpose for taps on some transformers
taps allow for the primary voltage to be raised and lowered
