Electric Machines Final

If a transformer is connected to a DC source, the transformer will overload at the ___. a. contacts b. primary coil c. secondary coil d. core

b. primary coil

+One factor that determines the frequency of an alternator is the ___. a. number of turns of wire in the armature coil b. speed of the rotor c. strength of the magnets used d. strength of the output voltage

b. speed of the rotor

In electric circuit schematics, a transformer is represented by which of the symbols shown in the illustration? A B C D

A

The output voltage of a 440 volt, 60 hertz, AC generator is controlled by the ___. a. prime mover speed b. strength of the excitation field c. load on the alternator d. number of poles

b. strength of the excitation field

The frequency of an AC generator is controlled by the ___. a. rheostat b. governor c. exciter d. capacitor

b. governor

+An AC generator produces 60 hz at 1800 rpm. If the generator speed is increased to 1830 rpm, the cycles will ___. a. remain at 60 hz b. increase to 61 hz c. decrease to 59 hz d. increase to 63 hz

b. increase to 61 hz

As shown in the illustration, part "X" of the diagram is known as a/an ____. a. commutator b. interpole c. starting pole d. auxiliary pole

b. interpole

+In a series wound motor, the current passing through the field windings is also passing through the ___. a. armature b. shunt field c. reactance comparator d. laminations

a

+The speed of a series wound winch motor is controlled by ___. a. varying the voltage applied to the motor b. the weight of the load on the cargo boom c. overcurrent protection devices in the motor d. a hydaulic speed-limiting governor

a

+Which of the following operating characteristics for DC motors is considered to give high starting torque? a. series b. shunt c. cumulative-compound d. differential-compound

a

As shown in the illustration, the DC motor's direction of rotation is changed by changing the ___. a. polarity of the generator field b. direction of three-phase motor rotation c. direction of generator rotation d. polarity of the motor field

a

If a unloaded DC compound motor's shunt field were weakened by rheostat resistance or by an open circuit, the motor would ___. a. overspeed due to reduced CEMF b. stop because of low flux c. continue to run at base speed d. slow down and overhead

a

In DC motor construction, the armature coils' ends are ___. a. soldered to the commutator bar risers b. imbedded into core slots c. crimped together with brush pigtails d. spliced with the field windings

a

In order to change the direction of rotation of a DC motor. I) the field leads must be changed II) the input leads must be changed a. I only b. II only c. both d. neither

a

Shunt, series, and compound wound motors, are all DC motors designed to operate from ___. a. constant potential, variable current DC sources b. variable potential, constant current DC sources c. variable potential, variable current DC sources d. constant potential, constant current DC sources

a

The counter EMF of a DC motor is maximum when the ___. a. motor is at rated speed b. armature is not turning c. motor is almost up to rated speed d. armature has just begun to turn

a

The primary function of an electric motor is to ___. a. develop torque b. generate high voltages c. produce a magnetic field d. generate high electrical resistance

a

In the illustrated three phase alternator, line voltage is equal to ___. a. 1.73 times the phase voltage b. the phase voltage c. the phase voltage divided by 1.73 d. the line current

a. 1.73 times the phase voltage

The turns ratio of device "A" shown in the illustration is 4:1 and all taps are equally spaced. If 440 volts were applied between 'H1' and 'H4', what would appear across 'X1' and 'X4'? a. 110V b. 220V c. 440V d. 1760V

a. 110v

Figure "D" of the diagram shown in the illustration has a turns ratio of 4:1. If a three-phase 440 volt supply is connected to terminals 'A-B-C', what voltage should develop across terminals 'a-b-c'? a. 64v b. 110v c. 190v d. 762v

a. 64v

Which of the following statements is true concerning all three-phase alternators? a. Each has three separate but identical armature windings acted on by one system of rotating magnets. b. each has one armature winding acted on by thee identical but separate system of rotating magnets all three-phase alternators are designed to operate with a 0.8 leading power factor the three phases always provide power to the load through three sets of slip rings and brushes

a. Each has three separate but identical armature windings acted on by one system of rotating magnets.

+AC and DC generators are similar that they ___. a. both initially generate alternating voltages b. both rectify the voltage before delivery c. both operate at 60 cycles d. both supply three-phase power

a. both initially generate alternating voltages

+In an AC generator, direct current from a separate source is passed through the windings of the rotor ___. a. by means of slip rings and brushes b. by means of a commutator c. by means of rotating bar magnet d. to minimize the danger of arc over

a. by means of slip rings and brushes

+The basic operating principle of a transformer is attributed to ___. a. electromagnetic induction b. variance of a conductor in a magnetic field c. mutual reaction d. thermionic emission

a. electromagnetic induction

+The frequency of an alternator at a given rpm is determine by the ___. a. number of turns of wire in the armature coil b. number of magnetic poles c. strength of the magnets used d. output voltage

b. number of magnetic poles

As load is added to an AC generator provided with constant field excitation, the prime mover slows down with the effect of ___. a. lowering frequency and lowering generated voltage b. increasing frequency and increasing generated voltage c. increasing frequency and lowering generated voltage d. lowering frequency and increasing generated voltage

a. lowering frequency and lowering generated voltage

The governor control switch of an alternator is moved to the 'raise' position. This action will ___. a. raise the no-load speed setting of the governor b. raise the percentage of speed droop c. lower the no-load speed setting of the governor d. lower the percentage of speed droop

a. raise the no-load speed setting of the governor

In a three-phase, open-delta connected transformer, the line current is equal to ___. a. the phase current b. three times the phase current c. the sum of any two phase currents d. the difference of any two phase currents

a. the phase current

The cycles per second developed by the alternator aboard your vessel is determined by ___. a. the speed o f the engine driving the alternator b. the resistance applied to the field rheostat c. the synchronous speed of induction d. the adjustments made to the voltage regulator

a. the speed o f the engine driving the alternator

+A load with an impedance of 440 ohms is connected across the secondary of a step-up transformer. If the input voltage is 110 VAC and the step-up ratio is 10, what will be the primary current? a. 2.5A b. 25A c. 250A d. none

b

+Hysteresis loss in transformers can be reduced by ___. a. laminating the core b. using special silicon steel materials c. using higher voltages d. using heavy gage wire

b

+The purpose of the commutator and brushes on a DC generator is to ___. a. transfer generated direct current voltage from the armature to the line b. convert the alternating voltage generated within the armature to a direct voltage c. provide a sliding contact method to excite the field d. reduce sparking between the armature and the carbon brushes

b

+What type of electric motor is commonly used to start small auxiliary diesel engines? a. synchronous b. series c. shunt d. cage

b

+Which of the following types of DC motors has its field connected in parallel with its armature? a. counter EMF b. shunt c. salient pole d. series

b

A motor enclosure which protects against falling liquids is classified as ___. a. waterproof b. drip proof c. spray tight d. spray proof

b

A three-phase alternator is operating at 450 volts with the switchboard ammeter indicating 300 amps. The kw meter currently indicated 163.6 KW with a power factor of 0.7. If the power factor increases to 0.8, the KW meter reading would increase by ___. a. 17.8 KW b. 23.3 KW c. 30.6 KW d. 37.8 KW

b

A three-phase alternator is operating at 450 volts with the switchboard ammeter indicating 300 amps. The kw meter currently indicated 163.6 KW with a power factor of 0.7. If the power factor increases to 0.8, the KW meter would then read ___. a. 181.4 KW b. 187.0 KW c. 194.2 KW d. 201.4 KW

b

Capacitors can be used in electric distribution systems to improve power factor. This is accomplished by seesawing energy between the capacitor and the ___. a. generator b. inductive loads c. resistive loads d. all of the above

b

In DC motor construction, commutating windings are wound on ___. a. opposite main poles b. interpoles c. adjacent main poles d. the rotor core

b

The counter EMF produced in the windings of a DC motor is 'zero' when the ___. a. armature has just begun to turn b. armature is not turning c. motor is almost up to rated speed d. motor is at rated speed

b

The full load torque of an electric motor is the ___. a. minimum torque developed by the motor accelerating from stop to full speed b. turning moment exerted by the motor at rated load and speed c. maximum torque developed by the motor with rated voltage and frequency d. turning moment exerted by the motor from any rotor angular position at any load

b

The item referred to as a pigtail on a DC motor brush rigging is a/an ___. a. feather spring b. uninsulated wire c. flexible spring adjuster d. brush holder

b

What is the function of the interpoles installed in DC motors? a. to provide greater torque by strengthening the main field b. to provide sparkless commutation without having to shift the brushes c. to limit the production of counter-electromotive force d. to limit the starting surge current

b

While standing an "at sea watch" onboard a DC diesel-electric drive ship, you notice that the kwatt load is at roughly 75% of capacity with a power factor less than 1. The reactive power (kvars) in the main power distribution would be ___. a. leading b. lagging c. zero d. infinity

b

What will be the phase angle relationship of a six-pole, three-phase, rotating field generator? a. 60 deg. b. 120 deg. c. 180 deg. d. 360 deg.

b. 120 deg.

What is the load voltage 'Es' as shown in the illustration? a. 292V b. 360V c. 450V d. 810V

b. 360v

+What will be the output frequency of a three-phase, six pole, AC generator operating at 1800 rev/min? a. 60hz b. 90hz c. 120hz d.180hz

b. 90hz

+Relative to the secondary winding of a step-up transformer, the primary winding will have ___. a. more turns b. fewer turns c. same number of turns but smaller wires d. twice as many turns

b. fewer turns

An autotransformer is equipped with a 50% tap, a 65% tap, and an 80% tap. Which of the following statements is true concerning a load connected to the 50% tap? a. the load is receiving minimum voltage and minimum current b. the load is receiving maximum voltage and maximum current c. the load is receiving maximum voltage and minimum current d. the load is receiving maximum voltage and maximum current

b. the load is receiving maximum voltage and maximum current

The function of a stepdown potential transformer is to reduce the load ___. a. voltage and current b. voltage and increase line current c. current and increase line voltage d. power

b. voltage and increase line current

+A load is connected to the secondary of a power transformer and the current through the load is 10 A. If the transformer has a step-up ratio of 1o and the input voltage to the primary is 110 VAC, what will be the current flow through the primary? a. 1 A b. 10 A c. 100 A d. 1000 A

c

+An advantage of DC motors over AC motors is that they ___. a. are less expensive b. require less maintenance c. offer infinite speed variation d. all of the above

c

+Which of the listed conditions will occur if the polarity of the field poles and the direction of current to the bushes of a DC motor were both reversed? a. the motor would not start b. the direction of rotation of the armature would be reversed c. the direction of rotation of the armature would be unchanged d. the field pole windings would become overheated

c

If the connections for the field and the armature on the DC motor are reversed, ___. a. the motor will run as a generator b. the motor will not run c. the direction of rotation will be the same d. the direction of rotation will be reversed

c

In a compound-wound motor, a portion of the line current flows through the ___. a. inertial poles b. stator c. shunt field coils d. frame

c

Relative to the direction of rotation, a DC motor commutating pole has the same polarity as the ___. a. main pole following b. interpole following c. main pole preceding d. interpole preceding

c

The armature cores of the DC motors are constructed with laminations to ___. a. eliminate hysteresis b. minimize brush sparking c. reduce eddy current losses d. compensate for armature reaction

c

Which of the following statements describes what will happen when both the polarity of the field poles, and the direction of current to the brushes of a DC motor are reversed? a. The motor will not start b. The direction of rotation of the armature will be reversed c. The direction of rotation of the armature will remain the same. d. The field pole windings will become overheaded

c

Figure "C" of the diagram shown in the illustration has a turns ratio of 4:1. If a three-phase 440 volt supply is connected to terminals 'A-B-C', what voltage should develop across terminals 'a-b-c'? a. 26v b. 110v c. 190v d. 762v

c. 190v

Propulsion AC generators creating 4160 VAC use transformers to provide 119 volts to the automatic voltage regulator. The turns ratio of this transformer is ___. a. 4:1 b. 1:4 c. 35:1 d. 40:1

c. 35:1

What would be the voltage measure across the load as shown in the illustration. a. 225V b. 292V c. 360V d. 450 V

c. 360V

Which of the listed transformer used a single winding to produce voltage transformation? a. step-up transformers b. step-down transformers c. autotransformers d. isolation transformers

c. autotransformers

The frequency of an alternator is controlled from the main switchboard by adjusting the ___. a. frequency meter b. voltage regulator c. governor control d. synchroscope switch

c. governor control

Which of the following procedures should be used to determine the load of a three-phase, delta wound, AC generator? a. multiply the amps in one phase by three b. divide the total amps in all phases by three c. multiply the amps in one phase by the square root of three d. divide the total amps in all phases by the square root of three

c. multiply the amps in one phase by the square root of three

A transformer works on the basic principle of ___. a. self impedance b. attraction and repulsion c. mutual induction d. increasing power

c. mutual induction

Regarding the illustrated electrical schematic, 'S1-P', 'S1-Q', and 'S1-R' represents ___. a. capacitors b. normally-closed contacts c. normally-open contacts d. normally-closed pushbottom switches

c. normally-open contacts

+The frequency of an AC generator is adjusted by means of the ___. a. main alternator field rheostat b. exciter field rheostat c. prime mover governor control d. equalizing reactor

c. prime mover governor control

As shown in the illustration, the generator field is excited with DC current provided by ___. a. conductors 1, 2, and 3 b. inductor L1 c. rectifier CR1 d. winding S-2

c. rectifier CR1

The amount of voltage induced in the stator windings is a modern AC generator depends mainly on ___. a. the number of field poles energized b. the number of slip rings connected to the commutator c. the strength of the magnetic field d. all of the above

c. the strength of the magnetic field

+Which of the following statements is true concerning a stepdown transformer in an operating AC power circuit? a. both increase b. both decrease c. voltage decreases as current increases d. voltage increases as current decreases

c. voltage decreases as current increases

+A series wound DC motor has its armature and field connected in series with a resistor. When the motor is disconnected from its power supply, this motor with exemplify ___. a. the proper connections for across the line starting b. the proper connections for an automatic strip heater c. a reversing controller circuit d. dynamic breaking

d

+An advantage of DC motors over AC motors is that they ___. a. are less expensive b. require less maintenance c. can be started across the line d. offer a more effective means of controlling speed

d

+Insufficient brush pressure on a DC motor may cause ___. a. generator overload b. excess residual magnetism c. water vapor absorption d. sparking of the brushes

d

+Which of the following statements identifies the difference between the primary windings and the secondary windings of a 2:1 stepdown transformer? a. the secondary windings have twice as much resistance as the primary windings b. the secondary windings use smaller wires than the primary windings c. the secondary windings can only provide half as much current as the primary windings d. the secondary windings have half as many turns as the primary windings

d

If a DC motor hums, but does not run when energized, which of the listed conditions could exist? a. incorrect lead connections b. incorrect brush setting c. a dirty commutator d. all of the above

d

In the construction of DC motors, parts of both the series and shunt fields are wound on the ___. a. opposite main pole b. rotor core c. interpole d. same main pole

d

The amount of mechanical force or torque produced by an electric motor depends on the ___. a. strength of its magnetic field b. amount of armature current flow c. length of conductor in the field d. all of the above

d

The torque produced by a DC motor armature is the product of the force acting at the armature surface multiplied by ___. a. work done by the armature in one revolution b. effective armature diameter at which the force acts c. maximum moment arm at the center of rotation of the armature d. perpendicular distance to its center of rotation

d

Which of the following types of motors can be used for correcting power factor during normal operation? a. polyphase b. wound-rotor c. induction d. synchronous

d

A turbogenerator has a rated output of 1200 KW at 60 hz, with a no load frequency of 61.5 hz. What is its speed droop? a. 0.0103 b. 0.015 c. 0.0244 d. 0.025

d. 0.025

In the illustration, if the device in a "A" has a step-up ratio of 10:1, what voltage should be measured at the secondary if the primary is connected to 110 volts AC? a. 0 volts b. 11 volts c. 110 volts d. 1100 volts

d. 110 volts

The turns ratio of device "A" in the illustration is a step down 4:1 and all the taps are equally spaced. If 120 volts was indicated on the secondary between 'X1' and 'X2', what would be indicated across 'H1' and 'H4'? a. 30v b. 120v c. 480v d. 1440v

d. 1440v

+What will be the frequency of the three-phase, 16 pole, AC generator operating at 3000 rev/min? a. 60 hz b. 90 hz c. 180 hz d. 400 hz

d. 400 hz

Brushless generators are designed to operate without the use of ___. a. brushes b. slip rings c. commutators d. all of the above

d. all of the above

Three factors responsible for the change in voltage as load is applied to an AC generator are: 1) the drop in resistance in the armature, 2) the change in flux, and 3) the ___. a. armature winding speed b. inductance load drop c. coil pitch factor d. armature reactance voltage drop

d. armature reactance voltage drop

The most common type of AC service generator found aboard ship is the stationary ___. a. electromagnetic field, revolving armature type b. electromagnetic field, oscilatory armature type c. armature, oscilatory electromagnet field type d. armature, rotating electromagnetic field type

d. armature, rotating electromagnetic field type

Voltage generated by modern revolving field AC generators is fed to the bus by means of ___. a. brushes on a commutator b. brushes on slip rings c. slip rings on a commutator d. direct connections from the stator

d. direct connections from the stator

An alternator will fail to produce line voltage as a result of ___. a. a closed circuit breaker b. oxidized slip rings c. improperly staggered brushes d. excitation field failure

d. excitation field failure

+Increasing the load on the secondary windings of a transformer will cause a/an a. decrease in the primary voltage b. increase in the primary voltage c. decrease in the primary current d. increase in the primary current

d. increase in the primary current

+To increase the frequency of an operating AC generator, you should ___. a. increase the field excitation b. decrease the field excitation c. increase the number of magnetic poles d. increase the speed of the prime mover

d. increase the speed of the prime mover

How will the value of the output frequency change if the load is removed from a turbogenerator having a governor speed droop setting of 3%? a. it will remain unchanged b. it will decrease by approx. 3% c. it will become variable d. it will increase

d. it will increase

Power transformer are rated in ___. a. kilowatts-amps b. ampere-turns c. kilowatt-volts d. kilovoltamperes

d. kilovoltamperes

For the illustrated wiring of a three phase alternator, which statement is true about the current? a. phase current is 1.73 times the line current b. line current is 1.73 times the phase current c. there is no relationship d. line current is equal to phase current

d. line current is equal to phase current

+Transformers are used onboard ships with AC generators to ___. a. change line frequency value b. increase power output to modulating frequency controllers c. decrease power output to modulating frequency controllers d. provide different voltage values to operate various types of electrical equipment

d. provide different voltage values to operate various types of electrical equipment

When securing an AC generator, you should FIRST ___. a. open the generator circuit breaker b. switch the voltage regulator to 'manual' c. decrease the field excitation to minimum d. reduce the load on the unit

d. reduce the load on the unit

+AC generator circuits are protected against malfunctions due to prime mover power loss by the use of ___. a. main bus disconnect links b. a separate battery backup c. reverse current relays d. reverse power relays

d. reverse power relays

+When a low input voltage is imparted to a device which then delivers a high output voltage, the device is known as a ___. a. primary transformer b. secondary transformer c. stepdown transformer d. step-up transformer

d. step-up transformer

+When a transformer is used to step down voltage, the low voltage winding is ___. a. part of the core b. the primary coil c. not insulated d. the secondary coil

d. the secondary coil

+Which of the following statements is true concerning step-down transformer operation? a. the resistance on the primary side is lower than the secondary side b. the voltage to the primary side is the same as the voltage from the secondary side c. the current to the primary side is the same as the current from the secondary side d. the voltage to the primary side is greater than the voltage from the secondary side

d. the voltage to the primary side is greater than the voltage from the secondary side

Automatic voltage regulators provided on switchboards function to ___. a. regulate the AC load on the generator b. protect the switchboard from high voltage c. govern prime mover speed to control voltage d. vary the field excitation to the generators

d. vary the field excitation to the generators