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