MNG 335 Final
In DC motor construction, commutating windings are wound on
Interpoles
A low voltage source is being used for testing armature coils. A coil short circuit will be indicated by a...
Low or zero voltage reading, while the other coils will have higher readings
A delayed-action fuse is most frequently used in which of the listed circuits
Motor circuit
A circuit in which a fuse has blown would be considered as
Open circuit
An equalizing connection between two compound-wound DC generators when paralleled, serves to
Parallel the series fields of the generators
Time delayed or delayed action-type fuses are designed to
Permit momentary overloads without melting
Armature cores in a DC generator are made of laminated steel sheets to
Reduce eddy current losses
A generator is prevented from becoming motorized by the use of
Reverse power relay
Which of the following types of DC motors has its field connected in parallel with its armature
Shunt
The simplest method of controlling the terminal voltage of a compound-wound DC generator is with a
hand-operated field rheostat connected in series with the shunt field circuit
The mica used in the commutators of DC machinery is
harder than copper
Hysteresis in a direct current generator is indicated by..
heating of the armature core
Sparking at the brushes of a DC generator can be the result of
improper brush pressure, improper brush seating, reversed interpole polarity
Dc generator voltage is decreased by cutting
in field resistance
When DC generators are operating in parallel, the load should be divided
in proportion to their rated amperages
To correct for reversed residual magnetism in a self-excited DC generator, you must
insulate the brushes from the commutator and flash the field
A self-excited DC generator fails to come up to its normal 240 Volts, the cause may be
low armature speed
Fuse elements are made of zinc or any alloy of tin and lead, therefor, the melting point of the fuse element must be
lower than that of copper
One method of testing for a reversed shunt field coil in a DC generator or motor is by connecting the field to a direct current source, at reduced field rated voltage, and test for polarity using an
magnetic compass placed near each field
Relative to the direction of rotation, a DC motor commutating pole has the same polarity as the
main pole preceding
The function of the compensating windings used in a DC generator is to
neutralize armature reaction
A field rheostat, located in the shunt field coil circuit of a DC compound generator, permits adjustment of the
no-load voltage
An open shunt field in a direct current machine may be located by connecting the field circuit to an external power source, equal to the rated field voltage or less, and tested with a voltmeter from...
one line terminal to each coil lead in succession
An instantaneous trip-type fuse will
open as soon as the load current exceeds its set point
Undervoltage trips are frequently installed on switchboard circuit breakers to trip
out generators when there is low voltage in the main circuit
When the series field of a compound wound DC generator is proportioned to the shunt field, providing for increased voltage with increased load, the generator is known as
over compounded
When two generators are on the line and are sharing the load equally, they are said to be operating in
parallel
The term "copper loss", as applied to DC generators, refers to the
power lost as heat within the copper windings
The process of self-excitation in a DC generator begins as soon as the prime mover starts turning due to the
presence of residual magnetism in the field poles
A DC generator will fail to build up proper voltage if the
prime mover is turning too slow
Modern DC generators are fitted with commutating poles to
reduce sparking
Which of the following precautions should be taken when a blown fuse, rated at 10 amperes, is replaced?
replace blown fuse with one of equal voltage and ampere capacity
The field strength of the pole pieces in a self-excited DC generator has been lost. Properly flashing the field will result in
restoration of residual magnetism
The function of the commutator in a DC motor is to...
reverse the flow of current through the armature
In the construction of DC motors, parts of both the series and shunt fields are wound on the
same main pole
DC generator brush sparking, caused by coil inductance discharging at the moment of commutation, may be corrected by
shifting the neutral plane of the brush rigging
A circuit breaker and a fuse have a basic similarity in that they both
should open the circuit when overloaded
In DC motor construction, the armature coils' ends are
soldered to the commutator bar risers
If the generator pilot light is lit on a DC switchboard, this means
that power is available from the generator
In a three-wire DC generator, supplying loads at 240 volts and 120 volts, the current in the neutral line is
the difference between the currents in the positive and negative lines
Protection against sustained overloads occurring in molded case circuit breakers is provided by a
thermal acting trip
A reverse current relay prevents DC generator motorization automatically by
tripping the circuit breaker
Which of the terms listed best describes a compound-wound DC generator having a higher voltage at no load than at full load?
under compounded
Kilowatt load is divided between two DC generators operating in parallel by
varying the excitation voltage
A voltage regulator installed in a direct current generator serves the purpose of
varying the shunt field resistance
Prior to closing the circuit breaker when paralleling two DC generators, you must be certain that the
voltage of the incoming machine is at or slightly above the bus voltage
Fuses are rated in
voltage, amperage, interrupting capacity
To effectively clean a commutator in good physical condition, you should use...
A canvas wiper
To parallel two DC generators, you should start the prime mover,
Adjust the voltage, close the circuit breaker, and then balance the loads
Electrical circuits are protected against overhearing by means of...
Circuit breaker
The purpose of the commutator and brushes on a DC generator is to
Convert the alternating voltage generated within the armature to a direct voltage
Generator and motor brush pressures can be calculated by
Dividing the spring force by the brush contact area
The normal method of transferring loads between paralleled DC generators is to adjust the
Generator shunt field circuit resistance
How will a molded-case circuit breaker react after it has tripped, as a result of an overloaded circuit?
The breaker will trip again if immediately reset
Which of the methods listed is used to maintain the division of load between two compound-wound, DC generators operating in parallel?
The equalizer connection parallels the series fields of all machines
Which of the methods listed is used to maintain equal load sharing between two compound wound DC generators operating in parallel
The series fields of both generators are connected in parallel
Which of the following statements concerning an under compounded DC generator with an inherent voltage regulation of 10 percent is correct?
The voltage is 10 percent greater with no load than with full load
The item referred to as a pigtail on a DC motor brush rigging is...
Uninsulated wire
If the field connections of a self-excited DC generator are reversed, which of the following problems is most likely to occur
Voltage is unable to build up
Which of the following losses are present in every direct current generator armature
Winding copper loss, core eddy current loss, magnetic hysteresis loss
When paralleling two DC Generators, which of the following actions should be the final step
balancing the loads
Etched or burned bands on the contact faces of the brushes in a direct current generator can be caused by
brushes improperly positioned
In a DC generator, the effects of induced electromotive force are neutralized by the
commutating poles
The process whereby the internal alternating current in a DC generator is changed to direct current is known as
commutation
Brushes in a generator must be positioned in the neutral plane to avoid sparking between the brushes and the
commutator
Spacers are inserted at definite intervals between the laminations of the armature of a DC machine to
cool the armature
The arc resulting from the tripping of a circuit breaker is prevented from damaging the contacts by
directing the arc into an arc chute
A variable shunt, connected across the series field coils of a DC compound wound generator, to permit adjustment of the degree of compounding is called a
diverter
You can determine if a circuit breaker is tripped by
examining the position of the handle
Two direct current generators are operating in parallel at approximately 40% capacity. One of the generators may be taken off the line, while the voltage is kept constant by the use of the...
field rheostats to decrease field strength in the offgoing generator while increasing field strength in the remaining generator
A ground to main DC generator is indicated by the
ground detection system