Chapter 4: Power Generators
The flat 9-V battery, has how many cells in series? A. 3 B. 4 C. 6 D. 9
C
Electrical machines refer to machines that convert ________. A. mechanical to electrical energy B. electrical to mechanical energy C. electrical energy of one form to electrical energy of another form D. all of the above
D
The torque of a dc motor is A. directly proportional to the field strength B. inversely proportional to the field strength C. directly proportional to the armature current D. A and C are correct
D
The transformer that should never have the secondary open circuited when primary is energized is A. power transformer B. auto transformer C. voltage transformer D. current transformer
D
The yoke of a dc machine is made of A. silicon steel B. aluminum C. soft iron D. cast steel
D
To increase the voltage output, cells are connected in A. parallel B. series-parallel C. parallel-series D. series
D
Usually used to drive low-speed alternators A. diesel engines B. jet propulsion engines C. steam turbines D. hydraulic turbines
D
What gives the relative activity in forming ion charges for some of the chemical elements? A. Electrochemical series B. Electrical series C. Electromotive series D. Both A and C above
D
What is the approximate efficiency of large transformer? A. 65% B. 80% C. 50% D. 95%
D
What is the most common method used in varying the speed of a dc motor? A. by varying the supply voltage B. by changing the effective number of conductors in series C. by varying the armature resistance D. by varying the field strength
D
A battery is used to A. supply a steady dc voltage B. supply an unstable dc voltage C. supply an ac voltage D. supply an ac/dc voltage
A
A dc series motor is most suitable for A. cranes B. lathes C. pump D. punch presses
A
Alternators have less chance to hunt if driven by A. steam turbines B. hydroturbines C. diesel turbines D. nuclear reactor
A
Among the dc motors, which produces the highest torque? A. series B. shunt C. compound D. differentially compounded
A
Armature reaction in a dc motor is increased A. When the armature current increases B. when the armature current decreases C. when the field current increases D. by interpole
A
Motors whose speed can be easily controlled. A. dc motors B. ac motors C. ac & dc motors D. ac or dc motors
A
The armature of a dc machine is laminated in order to reduce A. Eddy current loss B. Copper loss C. Hysteresis loss D. Frictional loss
A
Which is a variable speed motor? A. series B. commutatively compounded C. shunt D. differentially compounded
A
A transformer operates poorly at very low frequencies because A. permeability of core is increased B. magnetizing current is abnormally high C. primary reactance is too much D. permeability core is reduced
B
After a shunt motor is up to speed the speed may be increased considerably by A. increasing field circuit resistance B. decreasing field circuit resistance C. increasing the armature circuit resistance D. reducing the load
B
By laminating the core of a transformer, __________ decreases A. leakage reactance B. eddy current loss C. hysteresis loss D. copper loss
B
For 20% increase in current, the motor that will give the greatest increase in torque is _________ motor A. shunt B. series C. differentially compounded D. commulatively compounded
B
For a given dc generator, the generated voltage depends upon A. flux only B. both speed and flux C. speed only D. armature rotation
B
For the same rating __________ motor has the least starting torque A. commulatively compounded B. shunt C. series D. differentially compounded
B
Four carbon zinc cell in series will provide about A. 2 Vdc B. 6 Vdc C. 9 Vdc D. 8 Vdc
B
High speed alternators are driven by A. diesel engine B. steam turbines C. hydraulic turbines D. diesel engine
B
High voltage dc machines use what winding? A. Lap B. wave C. either lap or wave D. open circuit
B
How long will a battery need to operate a 240 Watts equipment, whose capacity is 100 Ah and 24 volts rating? A. 5 hrs B. 10 hrs C. 1 hr D. 0.10 hr
B
If the lagging load power factor of an alternator is decreased, the demagnetizing effect of the armature reaction A. remains the same B. is increased C. is decreased D. becomes infinite
B
In a dc generator armature reaction __________ pole tip A. weakens the flux at the trailing B. weakens the flux at the leading C. strengthens the flux at the leading D. strengthens the flux at the trailing
B
In a very large dc motor with severe heavy duty, armature reaction effects are corrected by A. using interpole only B. using compensatory windings in addition to interpoles C. shifting the brush position D. fixing the brush position
B
In an auto transformer, the primary and secondary are ___________ coupled A. only magnetically B. magnetically as well as electrically C. only electrically D. directly
B
In applications where a high torque is needed during starting a _______ motor is preferred. A. dc shunt B. dc series C. differentially compounded D. cumulatively compounded
B
The demand for a large increase in torque of a dc shunt motor is met by a A. large decreased in speed B. large increased in current C. large increased in speed D. small increased in current
B
The greatest percentage of the heat loss in a dc machine is due to A. eddy current loss B. copper loss C. hysteresis loss D. frictional loss
B
The maximum flux produced in the core of a transformer is A. directly proportional to supply frequency B. inversely proportional to supply frequency C. inversely proportional to primary voltage D. inversely proportional to secondary voltage
B
The most commonly used method of speed control of a dc motor is by varying A. voltage applied to the motor B. field strength C. effective number of conductors in series D. armature circuit resistance
B
The number of parallel paths in a simplex lap winding is equal to A. 2 B. number of poles C. number of pair poles D. 1
B
The synchronous reactance of an alternator is due to A. leakage flux B. armature reaction C. dc field excitation D. hysteresis loss
B
What can be found in a transformer with open-circuit test? A. Copper losses B. Turns ratio C. Total equivalent resistance D. Total equivalent leakage resistance
B
What do you mean by break power transfer? A. The incoming generator will be connected first to the bus bar before disconnecting the existing generator. B. The present on-line generator will be disconnected first before connecting the incoming generator. C. The incoming generator will only be connected to the bus bar when the bus bar breaks. D. The present on-line generator will be disconnected first and then reconnected together with the incoming generator.
B
When the load on a transformer is increased, the eddy current loss A. is decreased B. remains the same C. is increased D. becomes zero
B
A _________ is a group of cells that generates electric energy from their internal chemical reaction A. battery B. regulator C. power supply D. solar energy
A
A cell whose chemical reaction is not reversible A. primary cell B. secondary cell C. rechargeable cell D. solar cell
A
A cell whose voltage is generated as a function of light A. photovoltaic cell B. thermoelectric cell C. photodiode D. LED
A
A commutatively compounded motor does not run at dangerous speed at light loads because of the presence of A. shunt winding B. interpoles C. series D. compensating windings
A
A primary cell with carbon and zinc as its positive and negative electrodes respectively, and an electrolyte of either a gel or paste. This is commonly known as dry cell. A. Leclanche cell B. Edison cell C. storage cell D. solar cell
A
A transformer is an efficient device because it A. is a static device B. uses capacitive coupling C. uses inductive coupling D. uses electric coupling
A
A transformer will work on A. ac only B. ac as well as dc C. dc only D. pulsating dc
A
A triplex wave winding will have _________ parallel paths A. 6 B. 4 C. 2 D. 8
A
A type of secondary cell that can be recharged but with an electrolyte that cannot be refilled A. Sealed rechargeable cell B. Sealed secondary cell C. Leclanche cell D. Alkaline cell
A
An ideal transformer is one which A. has no losses and leakage reactance B. does not work C. has the same number of primary and secondary turns D. has the same primary and secondary voltage
A
Back emf in a dc motor is maximum at A. no load B. half full load C. full load D. three fourth full load
A
Carbon brushes are used in a dc machine because A. carbon lubricates and polishes the commutator B. contact resistance is decreased C. carbon is cheap D. carbon is abundant
A
Combination of ac motor, dc generator, and exciter to provide adjustable voltage dc power to a dc motor. A. Ward-Leonard system B. Half wave SCR adjustable voltage supply C. Compound motor D. Universal motor
A
DC series motors are used in those applications where ____________ required A. high starting torque B. low no load speed C. constant speed D. variable speed
A
Damper windings are used in alternators to A. prevent hunting B. achieve synchronism C. reduce wind age losses D. reduce eddy current loss
A
Electrical machines that convert mechanical energy to electrical energy. A. generators B. motors C. cycloconverters D. frequency converters
A
Excessive sparking at the brushes may caused due to A. dirt on the commutator B. misalignment of machine C. loose coupling D. worn bearings
A
Factor(s) that affect friction and winding loses in dc motors. A. speed B. armature current C. interpoles D. armature resistance
A
For given number of poles (2) and armature conductors, a lap winding will carry ___________ a wave winding A. more current than B. same current as C. less current than D. half the current than
A
Galvanic cell is the other name of A. voltaic cell B. primary cell C. secondary cell D. solar cell
A
Generally, in dc generators A. The armature winding is rotated with respect to a stationary magnetic field produced by electromagnets or permanent magnets. B. The electromagnets or permanent magnets (magnetic fields) are rotated with respect to the stationary armature winding. C. Current is sent into the armature winding; or the armature winding is usually placed in a stationary laminated iron core and the rotating element may or may not be a set of magnet poles, it depends on the type of motor. D. The armature winding is supplied with current; or the armature is placed inside a set of radially supported magnetic poles.
A
If an ac generator is to be driven from prime mover having variable speed, such as aircraft engine, a ________ must be used. A. constant speed drive (CSD) B. regulator C. conditioner D. peak limited
A
If the excitation of an alternator operating in parallel with other alternators is decreased, its A. power factor becomes more leading B. output kW will change C. power factor becomes more lagging D. power factor becomes unity
A
If the excitation of an alternator operating in parallel with other alternators is increased above the normal value excitation of excitation its A. power factor becomes more lagging B. output current decreases C. power factor becomes more leading D. output kw decreases
A
In a compound generator, which field winding usually, has a lower resistance? A. series field winding B. shunt field winding C. armature winding D. excitation winding
A
In a lap winding, the number of the brushes required is equal to A. number of poles B. commutator pitch C. number of pairs of poles D. number of coils
A
In ac motors, generally A. current is sent into the armature winding; or the armature winding is usually placed in a stationary laminated iron core and the rotating element may or may not be a set of magnet poles, it depends on the type of motor. B. the armature winding is supplied with current; or the armature is placed inside a set of radially supported magnetic poles. C. the armature winding is rotated by a stationary magnetic field produced by electromagnets or permanent magnets. D. the electromagnets or permanent magnets (magnetic fields) are rotated with respect to the stationary armature winding.
A
In applications where an almost constant speed is required, a _______ motor is a good choice. A. dc shunt B. dc series C. cumulatively compounded D. differentially compounded
A
In case if a 4 pole machine, 1 mechanical degree corresponds to ________ electrical degree A. 2 B. 8 C. 4 D. 6
A
In changing power from one generator to another, what do you call the operational sequence wherein the incoming generator is connected first before removing the existing generator? A. No Break Power Transfer (NBPT) B. UPS C. LIFO D. Standby Power transfer
A
In choosing a motor for a particular application, what characteristic you should consider? A. speed-torque B. speed-armature current C. speed efficiency D. speed power
A
In dc motors, when does severe arcing happens? A. during starting B. during rated speed C. during speed fluctuation D. during shutdown
A
In electrical power distribution, what do you call the first distribution line from the main generating station? A. main transmission lines B. primary distribution lines C. sub transmission lines D. secondary distribution lines
A
In motors of the same rating, which has the least starting torque? A. dc shunt B. dc series C. differentially compounded D. cumulatively compounded
A
Intermittent sparking at the brushes of dc motor may be caused due to A. an open armature coil B. loose coupling C. intermittent load D. incorrect voltage
A
Low speed alternators are driven by A. hydraulic turbines B. steam turbines C. steam engines D. diesel engines
A
Machine in which torque is produced by the interaction of ac current in the stator and dc currents in the rotor turning synchronism A. synchronous motor B. induction motor C. squirrel cage motor D. stepper motor
A
One advantage of a cumulatively compounded motor is that it does not run widely at light loads, this feature is due to A. shunt winding B. brake winding C. series winding D. clutch winding
A
Silver cadmium is secondary cell with a nominal open circuit voltage of A. 1.1 V B. 1.2 V C. 1.5 V D. 1.35 V
A
Silver-cadmium cell has a nominal open-circuit voltage of A. 1.05 V B. 1.5 V C. 2.1 V D. 2.2 V
A
Synchronous type of ac-motor, A. uses a dc-generator to supply dc-excitation to the rotating field B. uses pulsating dc C. uses alternator D. has an ac or dc depending on the type of machine
A
The ac armature winding of an alternator is A. always star connected B. star delta connected C. generally delta connected D. pi connected
A
The amount of copper in the primary is _________ that of the secondary A. about the same as B. smaller than C. greater than D. twice
A
The armature of a dc machine is made of A. silicon steel B. cast steel C. wrought iron D. soft iron
A
The back emf or counter emf in a dc motor A. opposes the applied voltage B. aids the armature current C. aids the supplied voltage D. opposes the armature current
A
The common dry cell, which is a primary cell having a carbon positive electrode and a zinc negative electrode in an electrolyte of sal ammoniac and a depolarizer A. Leclanche cell B. Faure storage cell C. Lead acid cell D. Lithium cell
A
The core type transformer is generally suitable for A. high voltage and small output B. low voltage and high output C. high voltage and high output D. low voltage and low output
A
The deciding factor in the selection of a dc motor for a particular application is its _____ characteristics A. speed torque B. torque armature current C. speed armature current D. speed
A
The effect of armature reaction is to A. decreased the total flux B. make the air gap flux uniform C. increase the total flux D. make the flux constant
A
The field structure of a dc machine uses A. Salient pole arrangement B. Non salient pole arrangement C. Silicon steel D. Cast steel
A
The field winding of a dc shunt machine usually carries ___________ of the rated current of the machine A. 2% to 5% B. more than 20% C. 15% to 20% D. less than 0.5%
A
The field winding of an armature is _________ excited A. dc B. ac C. both ac and dc D. battery
A
The flux in the core of a single phase transformer is A. purely alternating one B. purely rotating one C. partly alternating and partly rotating D. constant
A
The friction and wind age losses in a dc motor depends upon A. speed B. armature current C. flux D. field and armature resistance
A
The main drawback of a dc shunt generator is that A. terminal voltage drops considerably with load B. shunt field circuit has high resistance C. generated voltage is small D. it is expensive
A
The maximum current a cell can deliver through a 0.01 ohm load during testing A. flash current B. surge current C. ideal current D. full-load current
A
The number of cycles generated in a 6 pole alternator in one revolution is A. 3 B. 5 C. 6 D. 2
A
The open circuit test on a transformer is always made on A. low voltage winding B. high voltage winding C. either low or high voltage D. neither low or high voltage
A
The synchronous reactance of an alternator _________ as the iron is saturated A. decreases B. remains the same C. increases D. becomes doubled
A
The temperature rise of a transformer is directly proportional to A. apparent power B. leakage reactance C. reactive power D. true power
A
The terminal voltage of a __________ generator vary widely with changes in load current A. series B. flat compounded C. shunt D. over compounded
A
The torque developed by a dc motor is directly proportional to A. flux per pole x armature current B. armature resistance x applied voltage C. armature resistance x armature current D. flux per pole x applied voltage
A
The voltage of the bus bar to which several alternators are paralleled may be raised by simultaneously ____________ of all alternators A. increasing field excitation B. decreasing field excitation C. increasing input to prime movers D. decreasing input to prime movers
A
The voltage output of a cell depends on A. its elements B. electromotive series C. its electrodes D. electrochemical series
A
The voltage regulation of an alternator with a power factor of 0.8 lagging is ____________ at unity power factor A. greater than B. the same as C. smaller than D. 100%
A
The winding of the transformer with greater number of turns will be A. high voltage winding B. low voltage winding C. either high or low voltage winding D. high power
A
Three cells connected in series from a A. battery B. voltage divider C. voltage multiplier D. hybrid
A
To increase current capacity, cells are connected in A. parallel B. series C. series- parallel D. parallel- series
A
Two essential parts in rotating generators A. electro/permanent magnets and armature winding B. electromagnets or permanent magnets and commutator C. commutator and armature winding D. brushes and commutator
A
Two things which are same for primary and secondary of transformer are A. ampere turns and voltage per turn B. resistance and leakage reactance C. current and inducted voltage D. number of turns and power
A
Volt is a unit of ____________. A. electromotive force B. energy C. force D. magneto motive force
A
What cell is used to detect infrared radiation, either its generated voltage or its change of résistance may be used as a measure of the intensity of the radiation? A. lead sulfide cell B. Faure storage cell C. infrared cell D. Leclanche cell
A
What is the nominal output of an automotive battery having six lead acid cells in series? A. 12 V B. 24 V C. 6 V D. 3 V
A
What is the output of a lead acid cell? A. 2.1 V B. 1.5 V C. 1.35 V D. 1.25 V
A
What is the purpose of laminating the field poles and armature of a dc machine? A. to reduce eddy current B. to avoid contaminants C. to provide isolation D. to beautify the machine
A
What is true about field poles in electric machines? A. there are always even number of them (exist by pair) B. there are always an odd number of them C. there are an even or an odd number of them D. none of the above
A
When the secondary of a transformer is short circuited, the primary inductance A. is decreased B. remains the same C. is increased D. becomes zero
A
Which dc motors whose speed is greatly affected by a change in load? It will even run away if the load is removed. A. series B. shunt C. cumulatively compounded D. differentially compounded
A
Which motor is used to start heavy loads? A. series B. differentially compounded C. shunt D. commulatively compounded
A
Which motor never use belt connected loads? A. Series B. Commulatively compounded C. Shunt D. Differentially compounded
A
Which of the following is the main function of a battery? A. To provide a source of steady DC voltage to fixed polarity B. To provide a source of steady dc voltage of variable polarity C. To provide a source of variable dc voltage of fixed polarity D. To provide a source of variable dc voltage of variable polarity
A
Which statement is true regarding alternators? A. high-speed alternators are smaller than low-speed B. low-speed alternators are smaller than high-speed C. high-power alternators are smaller than low-power D. high-voltage alternators are smaller than low-voltage
A
With alternators connected in parallel, the voltage of the system can be changed by A. changing the field excitation B. increasing the speed of the prime movers C. changing the rpm of the prime movers D. synchronizing the prime movers
A
the primary leakage flux links A. primary winding only B. secondary winding only C. both primary and secondary windings D. neither primary nor secondary windings
A
A 4 pole dc machine has magnetic circuits A. 2 B. 4 C. 8 D. 6
B
A dc compound generator having full load terminal voltage equal to the no load generator voltage is called __________ generator A. under compounded B. flat compounded C. over compounded D. un compounded
B
A dc motor is still used in industrial applications because it A. is cheap B. provides fine speed control C. is simple in construction D. has no replacement
B
A device that transforms chemical energy into electrical energy A. secondary battery B. cell C. battery D. primary battery
B
A machine with field excitation by both shunt and series windings A. complex machine B. compound machine C. universal machine D. shunt/ series machine
B
A motor takes a large current at starting because A. the armature resistance is high B. back emf is low C. back emf is high D. shunt field is producing weak field
B
A separately excited dc generator is not used because A. it is costly B. a separate dc source is required for field circuit C. voltage drops considerably with load D. it is bulky
B
A small 9V battery might be used to provide power to A. an electric stove B. an electronic calculator C. a personal computer D. a radio transmitter
B
A standalone solar power system A. relies on the electric utility at night B. uses solar panels and batteries C. requires the use of dry cells D. need a full wave rectifier
B
A transformer is so designed that primary and secondary windings have A. loose magnetic coupling B. tight magnetic coupling C. critical magnetic coupling D. good electric coupling
B
Calculate the voltage regulation of a generator having a no-load voltage of 220 V and a full load voltage of 180 V. A. 18% B. 22% C. 28% D. 32%
B
Considered as the main types of battery A. Lithium cell and alkaline B. Carbon-zinc dry cell and lead sulphuric wet cell C. Leclanche cell and carbon zinc D. Voltaic cell and lithium cell
B
DC machines which are subjected to abrupt changes of load are provided with A. interpole windings B. compensating winding C. equalizers D. copper brushes
B
Electrical machines that convert electrical energy to mechanical energy. A. generators B. motors C. rotary converters D. frequency converters
B
Find the output of a four (4) lead acid cells. A. 3.2 V B. 8.4 V C. 5.8 V D. 12 V
B
In a dc machine the number of commutator segments is equal to A. number of conductors B. number of coils C. twice the number of poles D. twice the number of coils
B
In a dc motor, the brushes are shifted from the mechanical neutral panel in a direction opposite to the rotation to A. decreased speed B. reduced sparking C. increase speed D. produce flat characteristics
B
In a dry cell, what will happen to the internal resistance as it aged? A. decreases B. increases C. remains constant D. decreases or increases, depends on the chemical composition
B
In a simplex wave winding, the number of parallel paths is equal to A. number of poles in the machine B. 2 C. number of pair poles D. 1
B
In a vacuum cleaner, ___________ motor is generally used A. shunt B. series C. commutatively compounded D. differentially compounded
B
In dc generator, what converts the alternating emf to DC? A. armature B. commutator C. diode D. alternator
B
In electrical machines, what do you call the set of conductors wound on laminated cores of good magnetic permeability? A. armature core B. armature winding C. rotary winding D. rotary core
B
In electrical power Generating/distribution Company, which do you think is their highest expenses? A. generation of power B. distribution of power to the consumers C. power transmission D. substations
B
In the short circuit test in a transformer, __________ winding is generally short circuited A. high voltage B. low voltage C. either low or high voltage D. neither low nor high voltage
B
One of the following is a false statement A. storage cell has a reversible chemical reaction B. carbon zinc cell has unlimited shelf life C. lead acid cell is rechargeable D. primary cell is not rechargeable
B
Output of automotive battery with six lead-acid cells in series A. 6 V B. 12 V C. 24 V D. 48 V
B
Overheating of a dc motor is often due to A. insufficient end play B. overloads C. loose parts D. rough commutator
B
Small Dc machines generally have __________ poles A. 4 B. 2 C. 6 D. 8
B
Substance, which generates a voltage when exposed to light. A. generating substance B. photovoltaic material C. thermoelectric generator D. hydroelectric generator
B
The ac armature winding of an alternator operates at __________ the field of winding A. the same voltage as B. much higher voltage than C. much lesser voltage than D. half the voltage than
B
The alternators driven by ____________ do not have a tendency to hunt A. diesel engines B. steam engines C. water turbines D. prime movers
B
The amount of back emf of shunt motor will increase when A. the load is increased B. the field is strengthen C. the field is weakened D. the load is decreased
B
The armature winding of a dc Machine is ____________ winding A. an open circuit B. a closed circuit C. partly open circuit and partly closed circuit D. lap
B
The armature winding of a dc machine is placed on the rotor to A. save iron B. facilitate commutation C. reduce losses D. reduce armature reaction
B
The brush voltage drop in a dc machine is about A. 0.1 V B. 2 V C. 10 V D. 20 V
B
The commutator pitch for a simplex lap winding is equal to A. number of poles of the machines B. 1 C. poles pairs D. 2
B
The current in armature conductors of a dc machine is A. pure dc B. ac C. pulsating dc D. pure dc plus pulsating dc
B
The open circuit test on a transformer gives A. copper losses B. iron losses C. friction losses D. total losses
B
The rating of an alternator is expressed in A. kW B. kVA C. HP D. KVAR
B
The real working Part of a dc machine is the A. commutator B. armature winding C. field winding D. stator
B
The rotor of a turbo alternator is made cylindrical in order to reduce A. eddy current loss B. wind age loss C. hysteresis loss D. copper loss
B
The running speed of a dc series motor is greatly affected by what factor? A. field excitation B. load C. armature resistance D. supply voltage
B
The salient pole construction for field structure of an alternator is generally used for _________ machine A. 2 pole B. 8 pole C. 4 pole D. 6 pole
B
The shaft torque in a dc motor is less than total armature torque because of _________ in the motor A. copper losses B. iron and friction losses C. field losses D. hysteresis loss
B
The speed of a dc motor is A. directly proportional to flux per pole B. inversely proportional to flux per pole C. inversely proportional to applied voltage D. inversely proportional to armature current
B
The stator of n alternator is wound for ____________ on the rotor A. a more number of poles than B. the same number of poles as C. less number of poles than D. twice the number of poles
B
The voltage per turn of the primary of a transformer is _________ the voltage per turn of the secondary A. more than B. the same as C. less than D. twice
B
This synchronous reactance of an alternator is generally ____________ armature resistance A. 5 times smaller than B. 10 - 100 times greater than C. 5 times greater than D. 10 times smaller than
B
To produce an output of 7.5v, how many carbon zinc cells are connected in series? A. 4 B. 5 C. 6 D. 3
B
What refers to a method in which the charger and the battery are always connected to each other for supplying current to the load A. Continuous charging B. Float charging C. Infinite charging D. On line charging
B
When can we get a maximum mechanical power from a dc motor? A. Eb = 0 B. Eb = ½V C. Eb = 1V D. Eb = 2V
B
When the load on an alternator is increased, the terminal voltage increases if the load power factor is A. unity B. leading C. lagging D. zero
B
Which motor has the best speed regulation? A. Series B. Shunt C. Commutatively compounded D. Differentially compounded
B
Why are the field poles and the armature of a dc machine laminated? A. to reduce the weight of the machine B. to reduce eddy current C. to decrease the speed D. to reduce armature reaction
B
A dc generator whose excitation is produced by a winding connected to its own positive and negative terminals. A. series generator B. separately excited shunt generator C. self-excited shunt generator D. compound generator
C
A galvanic cell resulting from difference in potential between adjacent on the surface of a metal immersed in an electrolyte A. NiCd cell B. lead acid cell C. local cell D. lithium cell
C
A junction between two conductors that exhibits electrical characteristics under condition of changing temperature A. pn junction B. photojunction C. thermoelectric junction D. hydroelectric junction
C
A method of converting chemical energy into electric energy by dissolving two different conducting materials in an electrolyte A. Battery B. Cell C. Voltaic cell D. Charging
C
A secondary cell whose active positive plate consists of nickel hydroxide, and active negative-plate material is powdered iron oxide mixed with cadmium. Its typical output when fully charged is VO = 1.2 V A. Leclanche cell B. dry cell C. Edison cell D. lead-acid cell
C
A series motor designed to operate on dc or ac A. Shunt motor B. Series motor C. Universal motor D. Compound motor
C
A storage battery in which the electrodes are grids of lead containing lead oxides that changes in composition during charging and discharging and the electrolyte is dilute sulfuric acid A. Leclanche battery B. Nickel cadmium battery C. Lead acid battery D. Faure storage battery
C
A transformer will have zero efficiency at A. full load B. half full load C. no load D. twice the load
C
A voltage source in a single container made from one or more cells combines in series, parallel, or series-parallel. A. photoelectric B. thermocouple C. battery D. piezo-electric
C
An alternator with a lagging power factor of 0.8 will have a ________ voltage regulation at unity power factor. A. 0% B. less than C. greater than D. 100%
C
Cumulatively compounded motors are used in applications where ____________ is required A. variable speed B. poor speed regulation C. sudden heavy loads for a short duration D. constant speed
C
DC shunt motors are used in those applications where ___________ is required A. high starting torque B. high no load speed C. practically constant speed D. variable speed
C
Dc motor that has the most stable speed. A. differentially compounded B. compound C. shunt D. series
C
Description used for generators trying to self-adjust its parameters before paralleling with on line generators. A. synchronizing B. sequencing C. jogging D. alighning
C
Difference between the speed of a rotating magnetic field and the associated rotor A. split B. salient pole C. slip D. pull out torque
C
Electrical machine that converts ac voltage to dc voltage, or vice versa. A. generator B. motor C. rotary converter D. frequency converter
C
Excessive motor vibration is caused by A. too much brush tension B. open armature coil C. worn bearings D. bent shaft
C
For the same rating, a dc machine has _________ an ac machine A. the same weight as B. less weight than C. more weight than D. half the weight than
C
For the same rating, the size of low speed alternator is ____________ that of high speed alternator A. about the same as B. less than C. more than D. twice
C
Generally in ac generators A. The armature winding is rotated by a stationary magnetic field produced by electromagnets or permanent magnets. B. Current is sent into the armature winding; or the armature winding is usually placed in a stationary laminated iron core and the rotating element may or may not be a set of magnet poles, it depends on the type of motor. C. The electromagnets or permanent magnets (magnetic fields) are rotated with respect to the stationary armature winding. D. The armature winding is supplied with current; or the armature is placed inside a set of radially supported magnetic poles.
C
Generation of voltage in a generator can only happen when? A. there is a rotary conductor B. there is a magnetic field in a conductor C. there is a relative motion between conducting wires and magnetic lines of force D. there is a relative motion between a conductor and electric field
C
If a power transformer is operated at very high frequencies then A. primary reactance is too much increased B. primary will draw large power C. core losses will be excessive D. core loss is negligible
C
If a transformer core has air gaps then A. reluctance of magnetic path is decreased B. hysteresis loss is decreased C. magnetizing current is greatly increased D. eddy current is increased
C
In a practical transformer, copper losses account for how many percent of the total losses? A. 75% B. 25% C. 85% D. 95%
C
In a wave winding, the commutator pitch is approximately equal to A. pole pitch B. thrice the pole pitch C. twice the pole pitch D. half the pole pitch
C
In alternators, what is the purpose of damper windings? A. it prevents over speeding B. it maintain constant speed C. it prevents hunting D. it protects overloading
C
In applications where sudden heavy loads happen for short duration, a _______ motor is the best choice. A. dc shunt B. dc series C. cumulatively compounded D. differentially compounded
C
In electrical machines, what type of voltage is generated at the armature winding? A. dc B. pulsating dc C. ac D. ac or dc depending on the type of machine
C
In paralleling ac generators, ________ is very important. A. voltage level B. current level C. phase angle D. internal resistance
C
Is usually used to drive high-speed alternators A. diesel engines B. pneumatic engines C. steam turbines D. hydraulic turbines
C
Leclanche cell is the other name of A. lead acid cell B. zinc chloride C. carbon zinc cell D. mercuric cell
C
Majority of alternators in use have A. revolving ac armature winding B. stationary field type construction C. revolving field type construction D. stationary ac armature winding View Answer:
C
The air gap in an alternator is __________ in an induction machine A. much shorter than B. about the same as C. much longer than D. one-half than
C
The common 9v flat battery for transistor radio has _____________ cells connected in series A. 12 B. 3 C. 6 D. 9
C
The core type transformer provides A. much longer magnetic pattern B. lesser average length per turn C. shorter magnetic path D. longer magnetic path
C
The coupling field between electrical and the mechanical systems of a dc machine is A. electric field B. both electric and magnetic fields C. magnetic field D. electromagnetic field
C
The demand for a large increase in torque of a dc series motor is met by a A. large decrease in current B. large increase in speed C. large decrease in speed D. small decrease in speed
C
The disadvantage of a short pitched coil is that A. harmonics are introduced B. waveform becomes non-sinusoidal C. voltage round the coil is reduced D. voltage round coil is increases
C
The distribution of load between two alternators operating in parallel can be changed by changing A. phase sequence B. field excitation of alternators C. driving torques of prime movers D. current direction
C
The effect of leakage flux in a transformer is to A. increase copper losses B. decrease copper losses C. cause voltage drop in the windings D. reduce eddy current losses
C
The efficiency of a transformer will be at maximum when A. leakage reactance of the two windings are equal B. resistance of the two windings are equal C. copper loss is equal to constant loss D. copper loss is zero
C
The efficiency of the turbo-alternator _____________ with increase in speed A. decreases B. remains the same C. increases D. becomes 100%
C
The frequency of emf generated in an 8 pole alternator at 900 rpm is A. 50 hz B. 120 hz C. 60 hz D. 240 hz
C
The frequency of the system with which several alternators are parallel can be increased by simultaneously __________ of all generators A. increasing the field excitation B. decreasing the field excitation C. increasing the speed of prime movers D. decreasing the speed of prime movers
C
The greatest percentage of power loss in a dc motor is due to A. wind age loss B. core loss C. copper loss D. friction loss
C
The iron losses in a dc motor depend upon A. flux only B. speed only C. both flux and speed D. temperature
C
The mechanical power developed in a dc motor is maximum when back emf is equal to _____ the applied voltage A. twice B. one third C. one half D. one fourth
C
The nature of armature winding of a dc machine is decided by A. front pitch B. back pitch C. commutator path D. number of coils
C
The running speed of a dc series motor is basically determined by A. field excitation B. armature resistance C. load D. applied voltage
C
The source of mechanical power to turn the rotors of alternators, large and small, A.C. and D.C. A. prime contactor B. primer C. prime mover D. prime user
C
The speed at which a 6 pole alternator should be drive to generate 50 cycles per second is A. 1500 rpm B. 500 rpm C. 1000 rpm D. 1200 rpm
C
The stator of an alternator is identical to that of a A. dc generator B. 1 phase induction motor C. 3 phase induction motor D. Rosenberg generator
C
The voltage regulation of an alternator is larger than of a dc generator because of A. large armature resistance B. large leakage reactance C. complex effects of armature reaction D. small armature resistance
C
The yoke of a dc machine carries _____ poke flux A. one third of B. two times of C. one half of D. one fourth of
C
To minimize arcing during starting of dc motors, a resistance should be added to limit the current in the ________. A. series field winding B. shunt field winding C. armature winding D. all of these
C
Transformers having ratings less than 5kva are generally A. oil cooled B. water cooled C. natural air cooled D. self cooled
C
What important characteristic you should consider in choosing a dc-generator? A. voltage capacity B. current capacity C. voltage vs. load D. power rating
C
What is the primary reason why carbon brushes are preferred over copper brushes in dc motors? A. they have low loss B. they are more strong C. they produce less arcing D. all of the above
C
What should be the speed of a 6-pole ac generator in order to have a frequency of 50 Hz? A. 100 rpm B. 500 rpm C. 1000 rpm D. 1500 rpm
C
What type of cell that cannot be recharged which cannot restore chemical reaction? A. nickel-cadmium cell B. secondary cell C. primary cell D. lead-acid wet cell
C
When a dc motor has no load, what will happen to the back emf? A. reduces B. increases C. becomes maximum D. becomes zero
C
When load is removed, the motor that will run at the highest speed is the _________ motor A. shunt B. commulatively compounded C. series D. differentially compounded
C
When the speed of a dc motor increases, its armature current A. increases B. remains the same C. decreases D. becomes infinite
C
Which DC machines are the most common? A. 2 pole B. 6 pole C. 4 pole D. 8 pole
C
Which of the following is not a primary cell? A. Carbon-zinc B. Zinc-chloride C. Edison cell D. Mercuric oxide
C
Which of the following is not a secondary cell? A. Silver-zinc B. Nickel-iron C. Silver-oxide D. Lead-acid
C
Which of the following is the main function of a dc motor? A. to generate power B. to change mechanical energy to electrical energy C. to change electrical energy to mechanical energy D. to change chemical energy to mechanical energy
C
Which winding in a dc-compound generator that is relatively made of fine wires? A. armature winding B. excitation winding C. shunt field winding D. series field winding
C
With alternators connected in parallel, the frequency of the system can be changed by A. increasing the field excitation B. decreasing the field excitation C. changing the rpm of the prime movers D. synchronizing the prime movers
C
With respect to the direction of rotation, interpoles on a dc motor must have the same polarity as the main poles A. ahead of them B. in parallel with them C. behind them D. beside them
C
Generally in dc motors A. the armature winding is rotated by a stationary magnetic field produced by electromagnets or permanent magnets. B. current is sent into the armature winding; or the armature winding is usually placed in a stationary laminated iron core and the rotating element may or may not be a set of magnet poles, it depends on the type of motor. C. the electromagnets or permanent magnets (magnetic fields) are rotated with respect to the stationary armature winding. D. the armature winding is supplied with current; or the armature is placed inside a set of radially supported magnetic poles.
D
Hot bearings of a dc motor may be caused by A. poor ventilation B. loose coupling C. incorrect voltage D. lack of dirty lubricant
D
How alternators rated? A. in Watts B. in kW C. in kVar D. in kVA
D
If a cell can be charged after it is depleted, it is considered as A. a secondary cell B. a storage cell C. an accumulator D. all of the above
D
In an alternator, the effect of armature reaction is minimum at power factor of A. 0.866 lagging B. 0.5 lagging C. 0.866 leading D. Unity
D
In batteries, the material used to insulate the positive plates from negative plates are technically called A. insulator B. break-point C. coupler D. separator
D
In dc motors, the emf developed which opposes to the supplied voltage. A. residual emf B. induced emf C. coercive emf D. counter emf or back emf
D
In electrical power distributions, what insulator is generally used? A. rubber B. wood C. plastic D. porcelain
D
It consist of a single coil rotated in a magnetic field and produces an A.C. voltage. A. field winding B. armature C. commutator D. elementary generator
D
Nickel-iron cells is a secondary cell with a nominal open- circuit voltage output of 1.2 and is otherwise known as A. Leclanche cell B. Galvanic cell C. Voltaic cell D. Edison cell
D
One causes why the shaft torque is less than the developed armature torque of a dc motor. A. eddy current B. field loss C. brushes loss D. friction loss
D
Output of six carbon-zinc cells connected in series A. 3 V B. 6 V C. 6.6 V D. 9 V
D
Substance used in photovoltaic cells A. Silicon B. Selenium C. Germanium D. All of these
D
The greatest eddy current loss occurs in the __________ of a dc machine A. field poles B. commutating process C. yoke D. armature
D
The lines which carry the energy from the transformer to a customer's services are called ________. A. main transmission lines B. primary distribution lines C. sub transmission lines D. secondary distribution lines
D
The size of a dc generator can be reduced by using A. lap winding B. high resistance winding material C. iron commutator D. magnetic material of high permeability
D
The speed of a __________ motor is practically constant A. commutatively compounded B. differentially compounded C. series D. shunt
D
What is the voltage regulation when the full load voltage is the same as no-load voltage assuming a perfect voltage source? A. 100% B. 1% C. 10% D. 0%
D
What term applies to the use of two or more generators to supply a common load? A. on-line operation B. series operation C. cascaded operation D. parallel operation
D
What will happen to a dc series motor when its load is removed? A. the motor will stop B. the motor speed remains the same C. the torque remains the same D. the motor will overspeed
D
What will happen to the dc shunt motor if the load torque greatly increases? A. the speed will decrease B. there will be a great increase in current C. the speed almost remains constant D. B and C are correct
D
When the primary of a transformer is connected to a dc supply A. a primary draw small current B. primary leakage reactance is increased C. core losses are increased D. primary may burned out
D
Which is the most suitable for punch presses? A. shunt motor B. differentially compounded motor C. series motor D. commutatively compounded motor
D
Which of the following is a dry storage cell? A. Leclanche cell B. Edison cell C. Mercury cell D. Nickel cadmium cell
D
Which of the most suitable motor fro elevator A. Series B. Differentially compounded C. Shunt D. Commutatively compounded
D
Why are carbon brushes preferable compared to copper brushes? A. they have longer life B. they have lower resistance C. they are cheaper D. they reduce sparking
D
a constant voltage source has A. High internal resistance B. minimum efficiency C. minimum current capacity D. low internal resistance
D
For what reason, why carbon brushes are widely used dc machines? A. it is abundant B. it is cheap C. it has a high voltage drop D. it lubricates and polishes the contacts
D
A 12 V battery is rated at 48 ah. If it must deliver an average of 2.0 A, how long will the battery last before it needs recharging A. 48 hrs B. 4 hrs C. 96 hrs D. 24 hrs
D
A battery is rated 20 A-hr and is delivering a current of 2 A. How long does it last? A. 1 hr B. 5 hrs C. 8 hrs D. 10 hrs
D
A battery means A. cells connected in series B. cells connected in parallel C. cells connected in series-parallel D. all of the above
D
A device that is capable of converting chemical energy into electrical energy A. generator B. battery C. converter D. cell
D
A graphical relation between the generated emf and the field current of a machine A. current generation curve B. voltage generation curve C. voltage current curve D. magnetization curve
D
A motor whose speed increases as the load is increased. A. series dc B. dc shunt C. cumulatively compounded D. differentially compounded
D
A series motor will over speed when A. the load is increased B. the armature circuit is open C. the field id opened D. load is removed
D
A storage battery in which the plates consist if lead antimony supporting grids covered with a lead oxide paste immersed in weak sulfuric acid A. Leclanche cell B. primary battery C. secondary battery D. Faure storage battery
D
AC machine in which the torque is produced by the interaction of currents in the stator and currents induced in the motor by transformer action A. squirrel cage motor B. stepper motor C. synchronous motor D. induction motor
D
An 8 pole duplex lap winding will have ____________ parallel paths A. 8 B. 32 C. 4 D. 16
D
An example of rechargeable dc source is an/a A. lithium battery B. photovoltaic cell C. optoisolator D. lead acid battery
D
As the load increases a, ____________ motor will speed up A. series B. commutatively compounded C. shunt D. differentially compounded
D
Connecting batteries of equal voltage in parallel A. multiplies the voltage available B. increases the internal resistance C. reduces the power available D. multiplies the current available
D
Considered as a variable speed motor A. compounded B. differentially compounded C. shunt D. series
D
Electrical machine that changes ac voltage at one frequency to another ac voltage at another frequency. A. generator B. motor C. rotary converter D. frequency converter
D
Electricity that is generated due to heat, as in thermocouple. A. thermodynamics B. thermojunction C. electric heater D. thermoelectricity
D
Factor(s) that affect iron losses in a dc motor. A. flux B. speed C. armature resistance and flux D. A and B are correct
D
Find the frequency in kilocycles per second in the armature of a 10 pole, 1,200 rpm generator. A. 100 B. 1000 C. 10 D. 0.1
D
For heavy-duty dc motor, how does the effect of armature reaction be corrected? A. using interpoles & brush shifting B. using interpoles C. using compensatory winding D. B & C are correct
D
For the same rating _____________ motor has the highest staring torque A. shunt B. differentially compounded C. commutatively compound D. series
D
