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WorksheetsEE PART 9 - GERALDINO REVIEWER
Total questions: 200
Worksheet time: 2hrs 40mins
Which of the following is true about the power drawn by a pure reactance?
A. It is a true power
B. It is a radiated power
C. It is an apparent power
D. It is an imaginary power
For the same peak value of voltage, which of the following waves has the lowest rms value?
A. Sine wave
B. Square wave
C. Triangular wave
D. Full-wave rectified wave
How does the inductive reactance of a circuit related to the frequency of the source voltage?
A. Directly proportional to frequency
B. Inversely proportional to frequency
C. Directly proportional to the square of frequency
D. Inversely proportional the the square of frequency
What are the currents flowing in L and C during parallel resonance?
A. They are both zero
B. They are equal in magnitudes and in-phase
C. They are equal in magnitudes and out of phase by 900
D. They are equal in magnitudes and out of phase by 180°
What is the reason why "three-wattmeter method" is not normally used to measure power in a three- phase circuit?
A. It is a complicated connection
B. It requires three wattmeters
C. The neutral is not available
D. The load is unbalanced
In a two-wattmeter method of measuring power in a three-phase system, if the reading of the two wattmeters are identical, what is the load power factor?
A. Zero pf
B. Unity pf
C. Less than 0.5 lagging pf
D. Less than 0.5 leading pf
What is the circuit behavior of a series RLC circuit above the self resonant frequency?
A. Inductive
B. Capacitive
C. Resistive
D. Either A or B, depending on the value of R
Power factor is defined as the ratio of which of the following?
A. Volt-ampere to watt
B. Watts to reactive volt-ampere
C. Volt-ampere reactive to volt-ampere
D. Watt to volt-ampere
What is the net reactance of a series RLC circuit?
A. Zero
B. XL-XC
C. XC-XL
D. XL+XC
What is real power drawn of a circuit if the current and voltage are out of phase by 90°?
A. Maximum
B. Minimum
C. Zero
D. Unity
The conductance and susceptance components in the admittance are what type of elements?
A. Series elements
B. Parallel elements
C. Either series or parallel, depending on values
D. Series-parallel elements
At series resonance what is the value of the voltage drop across L or C in relation to the supply voltage?
A. It is less than the supply voltage
B. It is equal to the supply voltage
C. It is more than the supply voltage
D. It is either less than or more than depending on the vaue of the resistance R
How can the power factor of an inductive circuit be improve?
A. Connect a series inductor
B. Connect a parallel inductor
C. Connect a series capacitor
D. Connect a parallel inductor
A transformer will work on what type of voltage?
A. dc only
B. ac only
C. Both do and ac
D. Any kind of supply voltage
For successful parallel operation of two single phase transformers, which one is the most essential condition required?
A. Percentage impedance are equal
B. Turn ratios are equal
C. KVA ratings are equal
D. Polarities are properly connected
Which one is true about an ideal transformer?
A. The windings has no resistances
B. The core has no losses
C. The core has infinite permeability
D. All of these
Which of the following are the same for both primary and secondary windings in a transformer?
A. Currents and induced emfs
B . Ampere-turns and voltage per turn
C. Resistances and leakage reactances
D. None of these
The magnetic coupling between the primary and secondary windings of a transformer can be increased by which of the following methods?
A. By changing the turns ratio of the transformer
B. By using a magnetic core material of low reactance
C. By increasing the number of laminations in the core
D. None of these since the magnetic coupling is always constant
In a transformer, what is the purpose of placing the primary on top of the secondary windings or vice-versa?
A. To reduce the copper loss
B. To reduce the iron loss
C. To reduce the winding resistance
D. To reduce the leakage reactance
The regulation of a transformer is least affected by changes in frequency at which loading?
A. Unity power factor
B. Leading power factor
C. Lagging power factor
D. All of these
Which of the following transformer banks is best suited for 3-phase, 4-wire service?
A. △-△
B. △-Y
C. Y-Y
D. Y-△
Which of the following transformer should never have its secondary windings open-circuited when its primary is energized?
A. Current transformer
B. Autotransformer
C. Step-up transformer
D. Potential transformer
What is the reason why transformers are rated in KVA instead of kW?
A. Load pf is normally not known
B. The KVA is fixed while the kW is dependent on load pf
C. Total transformer loss depends on volt-ampere
D. It is already customary that the rating is KVA, based on early transformers
What is the reason why the KVA rating of ann ordinary two-winding transformer is increased when connected as an autotransformer?
A. Transformation ratio is increased
B. Secondary voltage is increased
C. Secondary current is increased
D. Energy is transferred both inductively and conductively
At what load is the efficiency of a transformer be zero?
A. No load
B. Near full load at unity pf
C. Overload at leading pf
D. Underload at lagging pf
When an V-V bank is converted to a A-A bank, what is percentage increase in each capacity?
A. 66.7%
B. 73.2%
C. 173.2%
D. 141.4%
Which of the following cannot be change by a transformer?
A. Voltage
B. Current
C. Impedance
D. Power
Which one is the main cause of the noise in transformer?
A. Magnetic flux
B. Alternating current in the windings
C. Cooling oil which is heating up
At what loading condition on a power transformer is efficiency maximum?
A. No load
B. Half load
C. Near full load
D. A little more than full load
How does the voltage per turn in the primary windings related to the voltage per turn in the secondary windings?
A. Equal
B. Less than
C. Greater than
D. Either B or C depending on step-up or step down applications
The eddy current loss in a transformer are reduced by laminating the core, the laminations being insulated from each other by which of the following?
A. Thick paper
B. Thin sheets of mica
C. Light coat of core plate varnish
D. Thin sheets of copper
Which of the following transformer connections of a transformer will give the highest secondary voltage?
A. Delta primary, delta secondary
B. Delta primary, star secondary
C. Star primary, star secondary
D. Star primary, delta secondary
The heat in a transformer core is dissipated by which of the following?
A. Insulating the jacket
B. Varnishing the windings
C. Covering the core with insulating coating
D. Steel punchings
Which one is true about an autotransformer?
A. It has two separate windings connected in series
B. It has no secondary windings
C. It is best suited in stepping up the voltage only
D. It has only one winding
Which of the following is true in a distribution transformer?
A. The all-day efficiency is more than the commercial efficiency
B. The all-day efficiency is less than the commercial efficiency
C. The all-day efficiency is equal to the commercial efficiency
D. None of these
What is the purpose of putting the transformer windings and cool the windings under oil?
A. To lubricate
B. To insulate and lubricate the windings
C . To insulate and cool the windings
D. To insulate, cool and lubricate the windings
Which of the following is true about a transformer?
A. The per unit resistance, reactance and impedance are the same, whether its referred to primary or secondary side
B. If the power factor is leading the regulation of a good transformer is higher than when it has a lagging power factor
C. The efficiency of a transformer is maximum when it is underload and operating at unity pf
D. A good transformer must have regulation as high as as possible
Which one dictates the primary current in a CT?
A. The core of the transformer
B. The load current
C. The secondary burden
D. All of these
Out of the following transformer bank connections which one is best to apply for three to two phase conversions?
A. Scott
B. Double Scott
C. Star/star
D. Star/double-delta
The no load input power of a transformer is practically equal to which of the following?
A. Copper loss at no load
B. Friction and windage loss
C. Stray power loss
D. Iron loss
What is the reason why the cores of large transformer are built up to nearly circular cross section?
A. To reduce leakage reactance
B. To reduce eddy current loss
C. To reduce iron loss
D. To reduce copper loss
What principle is used in transformer?
A. Static induction
B. Dynamic induction
C. Self induction
D. Mutual induction
What is the purpose of connecting sometimes a "reactor" in series to a transformer?
A. To deliver more KVA
B. To control the fault current
C. To correct its operating power factor
D. To improve its voltage regulation
In a transformer the energy from the primary of the transformer is transferred to the secondary due to which of the following?
A. Due to the flux linkage between the two windings
B. Due to the electrical connection between the two windings
C. Due to the difference in the number of turns in the primary and secondary windings
D. Due to changes the current in the two windings
What is the reason why a transformer is an efficient device?
A. It is a static device
B. It uses both inductive & capacitive coupling
C. Its winding has less resistance
D. Its friction and windage loss is small
The increased in the KVA capacity produced by connecting a two winding transformer as an autotransformer is due to which of the following?
A. Increased in the secondary voltage
B. Increased in the transformer efficiency
C. Increased in turns ratio
D. Establishment of conductive link between primary and secondary
In the transformer equivalent circuit, the core loss is represented by which of the following circuit element?
A. A series resistance
B. A series inductance
C. A shunt resistance
D. A shunt inductance
Which of the following is not important with transformers?
A. Casing
B. Primary windings
C. Secondary windings
D. Contacts
What is the purpose of stampings in transformers?
A. To reduce the hysteresis loss
B. To reduce the eddy current loss
C. To reduce the copper loss
D. All of these
The cores of transformers is normally made from which of the following materials?
A. Silicone steel
B. Seasoned wod
C. Annealed copper
D. Aluminum
In a power transformer, which winding is nearer to the iron core?
A. High voltage winding
B. Low voltage winding
C. Either high or low voltage winding
D. None of these
Which of the following is true about the primary and secondary induced emfs in a transformer?
A. They are always equal in magnitude
B. They are always anti-phase with each other
C. They are always in-phase with each other
D. They are always dependent on the load connected on the secondary side
In a transformer, what does the ratio 20:1 means?
A. There are 20 turns on primary, one turn on the secondary
B. The secondary voltage is 1/20th of primary voltage
C. The primary current is 20 times greater than the secondary current
D. For every 20 turns on primary, there is one turn on the secondary
What is the purpose of a tap changing transformer?
A. To supply low voltage for instruments
B. To step the voltage
C. To step down the voltage
D. To step up as well as step down the voltage
Which one is an essential feature of an autotransformer?
A. It uses only one winding
B. It is more suited for single-phase supply
C. It is completely automatic in its operation
Which of the following is a not a basic element of a transformer?
A. Core
B. Primary winding
C. Secondary winding
D. Mutual flux
The core of a transformer must posses which of the following characteristics?
A. Low permeability and high hysteresis
B. Low permeability and low hysteresis
C. High permeability and low hysteresis
D. High permeability and high hysteresis
At what condition will the efficiency of a tum transformer be maximum?
A. Resistance of both windings are equal
B. Copper loss is equal to core loss
C. Per unit impedance of both windings are equal
D. Load served is a unity of load
Which of the following cannot be done by a transformer?
A. Increase the output power
B. Increase the output impedance
C. Increase the output voltage
D. Increase the output current
What is the cause of the humming sound in a transformer?
A. Transformer winding
B. Transformer oil
C. Magnetostriction
D. Size of transformer tanks
The all day efficiency of a transformer is ( ) electrical efficiency of the same transformer.
A. equal to
B. less than the
C. greater than the
D. either less than or greater than the
Which loss will decrease when the load of the transformer will decrease?
A. Copper loss
B. Eddy current loss
C. Hysteresis loss
D. All of these
What is the purpose of using a higher flux density in a transformer?
A. To decrease the weight per KVA
B. To increase the weight per kVA
C. To decrease the weight per kW
D. To increase the weight per kW
The temperature rise in a transformer is directly proportional to which of the following?
A. Leakage reactance
B. Supply frequency
C. Apparent power
D. Reactive power
In general, what is the most important point to monitor during the operation of a transformer?
A. Primary voltage
B. Core loss
C. Exciting current
D. Temperature
What is the percentage equivalent of the no load current in comparison to the full load current of a transformer?
A. About 1 to 2%
B. About 2 to 5%
C. About 5 to 10%
D. About 10 to 20%
What is the purpose of a "breather" in a transformer?
A. It is used to blast air to the transformer tank
B. It is used to supply oil to the transformer tank
C. It is used to prevent the transformer windings inside the transformer tank from overheating
D. It is used to extract moisture of the air that enters the transformer tank
Which of the following will happen when a transformer is plugged into a DC circuit?
A. It would blow a fuse
B. The secondary will burn out
C. The primary will overload and the secondary will be dead
D. All of these
Which of the following tests is used to determine the relative polarity of the windings of a transformer?
A. Short circuit test
B. Phasing out test
C. Back to back test
D. Open circuit test
When a closed A bank is converted into an open bank, each of the two remaining transformers supplies what percent of the original load?
A. 50%
B. 57.7%
C. 73.2%
D. 66.7%
What is the purpose of the no-load test in a transformer?
A. To determine copper loss at no load
B. To determine the smallest current it can carry
C. To determine the efficiency of the transformer
D. To determine the magnetizing current and no load losses
What is the purpose of the iron core in a transformer?
A. To provide tight magnetic coupling
B. To electrically connect the primary and secondary windings
C . To mechanically balanced the transformer
D. To reduce the core loss
Two transformers when operating in parallel will share the load depending on which of the following?
A. Leakage reactance
B. Efficiency
C. Per unit impedance
D. Magnetizing current
At what power factor does the transformer operates?
A. Always unity pf
B. Always lagging pf
C. Always leading pf
D. At a pf depending on load pf
Buchholz relay is used in transformers. Which one is true about a Buchholz relay?
A. It is an oil actuated relay
B. It is a gas actuated relay
C. It is a current actuated relay
D. It is an oil-temperature actuated relay
What is the purpose of the open circuit test in a transformer?
A. To determine full load copper loss
B. To determine total losses
C. To determine the iron loss
D. To determine the power output at no load
Transformer actions require which of the following fluxes?
A. Constant magnetic flux
B. Alternating magnetic flux
C. Pulsating magnetic flux
D. No flux is needed
What is being increased in a step up transformer?
A. Voltage
B. Current
C. Power
D. All of these
What will happen if a power transformer is supplied at very high frequency in the primary?
A. Transformer will draw more kw
B. Voltage in the secondary side will be high
C. Primary side will drawn more current
D. Core loss will be very high
What is the resistance of the low voltage winding in comparison to the high voltage winding in a transformer?
A. It is equal
B. It is less than
C. It is greater than
D. It can be less or greater, depending on usage of the transformer
When a transformer winding suffers a short circuit, what type of force will be experienced by the adjoining turns of the same winding?
A. An attractive force
B. A repulsive force
D. Any of these
In a transformer, the primary leakage flux links which of the following windings?
A. Primary windings only
B. Secondary windings only
C. Both primary and secondary windings
D. Not in the primary nor in the secondary windings
Instrument transformers are used on AC circuits for extending the range of which of the following instruments?
A. Ammeter
B. Voltmeter
C. Wattmeter
D. All of these
What is being "transform" in a transformer?
A. Power
B. Current
C. Voltage
D. Frequency
The eddy current losses in a transformer varies ( ) the supply voltage.
A. inversely with
B. directly with
C. inversely to the square of
D. directly to the square of
What will happen to the transformer if the primary is connected to a dc supply?
A. The core loss will increase
B. The primary may get burn out
C. The primary will draw less current
D. Nothing serious will happen
The eddy current loss in a transformer is directly proportional to which of the following?
A. Thickness of core laminations
B. The supply frequency
C. The square of thickness of core laminations
D. The flux density of the core
Which part of the transformer is most subjected to damage due to overheating?
A. Iron core
B. Frame or casing
C. Winding insulation
D. Copper windings
What is a conservator in a transformer?
A. It is an air-tight metal drum located at the top of a transformer tank
B. It is the metal tank of a transformer that housed the core and the windings
C. It is a protective device that protects the transformer from overloading
D. It is a protective device that protects the transformer from lightning surges
In a transformer, at every instant the direction of the secondary current must be such as to oppose any change in flux. This is under which of the following principles?
A. Coulomb's law
B. Faraday's law
C. Joule's law
D. Lenz' law
What is the purpose of an autotransformer in the motor starting circuit?
A. To limit the current
B. To reduce the voltage
C. To keep constant amperage
D. To provide reliable voltage
Before removing the ammeter from a current transformer, its secondary must be short circuited 191 in order to avoid which of the following?
A. Excessive heating of the core
B. High secondary emf
C. Increase in the iron loss
D. All of these
Which winding in a transformer has more turns?
A. Primary windings
B. Secondary windings
C. High-voltage windings
D. Low-voltage windings
Which one is the most common cause of contamination of water in the oil used in transformer located indoors?
A. Leaky bushings
B. Condensation of moisture from air in the tank
C. Decomposition of foreign matters in the oil
D. None of these
Transformers are rated in what unit?
A. KVA
B. KW
C. kV
D. KVAR
What is the main function of the iron core in a transformer?
A. To provide mechanical strength to the windings
B. To reduce the eddy current loss
C. To provide electrical linkage to the two windings
D. To reduce the reluctance of the magnetic path
What is the relationship between the induced emf and the core flux in a transformer?
A. The induced emf lags the core flux by 90°
B. The induced emf leads the core flux by 90°
C. The induced emf is in-phase with the core flux
D. The induced emf is independent of the core flux
What is the typical usage of an autotransformer?
A. Current transformer
B. Variable transformer
C. Isolating transformer
D. Control transformer
As compared to A-A transformer bank, what is the percentage capacity of the V-V bank?
A. 66.7%
B. 86.6%
C. 57.7%
D. 73.3%
What is the reason why transformers operate poorly at very low frequencies?
A. Magenetizing current is high
B. Permeability of the core will increase
C. Primary reactance is too much increased
D. Copper loss is high
At relatively light loads, the efficiency of a transformer is low. Why?
A. Secondary output is low
B. Transformer losses are high
C. Copper loss is small
D. Fixed loss is high in proportion to the output
What is the main purpose of having a core in a transformer?
A. To decrease the iron losses
B. To prevent the eddy current loss to happen
C. To eliminate the magnetic hysteresis
D. To decrease the reluctance of the common magnetic circuit
What type of coupling is used in the primary and secondary windings of a transformer?
A. Electrical
B. Mechanical
C. Magnetic
D. All of these
Which one is a method of cooling used in a transformer rated 5 KVA or less?
A. Oil cooled
B. Natural air cooled
C. Hydrogen cooled
D. Water cooled
What is the reason why open circuit test is performed on the low voltage winding of the transformer?
A. It draws sufficiently large current on load current for convenient reading
B. It requires lesser voltage to perform the test
C. It needs only minimum power input to perform the test
D. It involves only lesser core loss, which means more efficient results
Tappings in a transformer are provided where?
A. At the phase end of the high voltage side
B. At the middle of the high voltage side
C. At the neutral end of the high voltage side
D. At the phase end of the low voltage side
Which of the following is defined as the "voltage transformation ratio"of a transformer?
A. Ratio of secondary induced emf to primary induced emf
B. Ratio of secondary terminal voltage to primary applied voltage
C. Ratio of primary turns to secondary turns
D. Ratio of secondary current to primary current
At no load, the primary input is approximately equal to the iron loss. Why?
A. The primary current is small
B. The secondary current is small
C. Both the primary and secondary currents are small
D. The transformer has no output
If the impedance triangle of two transformers operating in parallel are not identical in shape and size, which of the following is true?
A. The two transformers will share the load equally
B. The two transformers will get overheated
C. The two transformers will run with different pf
D. The two transformers will have a circulating current even when unloaded
Which of the following is called the "voltage transformer ratio"?
A. E1/E2
B. E2/E1
C. N1/N2
D. N2/N1
What will happen if the flux density in a transformer will be increased?
A. The size of the transformer will be reduced
B. Both hysteresis and eddy current losses will be reduced
C. The distortion of the voltage wave shape will be reduced
D. All of these
What is an ideal transformer?
A. A transformer that does not work
B. A transformer that has only one winding
C. A transformer whose primary and secondary windings are equal in turns
D. A transformer that has no losses and leakage reactance
Which of the following is true about a step-up transformer?
A. It will decrease the voltage and increase amperage
B. It will decrease both voltage and amperage
C. It will increase the voltage and decrease amperage
D. It will increase both voltage and amperage
What is the normal range of the efficiency of a transformer?
A. 90 to 98%
B. 80 to 90%
C. 70 to 80%
D. 60 to 70%
Which one is a purpose of cooling transformers?
A. To reduce the humming sound
B. To reduce the losses
C. To increase the efficiency
D. To dissipate the heat generated in the windings
During the short circuit test, which winding is short circuited?
A. Primary windings
B. Low voltage windings
C. Secondary windings
D. High voltage windings
What is the reason why leakage flux occurs in a transformer?
A. Transformer is not an efficient machine
B. The core has a very high permeability
C. There is no electrical linkage between windings
D. Air is not a good magnetic insulator
Under what type load pf will a transformer has a negative voltage regulation?
A. Unity pf
B. Lagging pf
C. Leading pf
D. Zero pf
Which one will reduce the eddy current loss in a transformer?
A. By increasing the thickness of core laminations
B. By decreasing the thickness of core laminations
C. By using higher gage wires in the windings
D. By decreasing the air gap in the magnetic circuit
What is the reason why at no-load the power factor of the transformer is low?
A. Exciting current Io is negligible at no-load
B. The magnetizing component of the exciting current Io is too small
C. The magnetizing component of the exciting current I, is large
D. None of these
What is the usual secondary current rating of a current transformer used for meters and relays?
A. 5 A
B. 10 A
C. 1 A
D. 100 A or more
The following statements are the requirement in the parallel operation of two transformers. Which one is not correct?
A. Transformers must have equal voltage ratio
B. Transformers must have the same ratio of transformation
C. Transformers must be operated at the same frequency
D. Transformers must have equal KVA ratings
What is common to the two windings in a transformer?
A. Magnetic circuit
B. Number of turns
C. Electric current
D. Voltage induced
During the short circuit test, the iron loss of a transformer is negligible. Why?
A. The entire input power is just enough to meet the copper losses
B. The iron losses becomes totally sat
C. Supply frequency is held constant action of the normal flux
D. The flux produced is only a small fr
Which of the following is an essential condition for parallel operation of two single phase transformers?
A. They should have the same voltage ratio
B. They should have the same per unit impedance
C. They should have the same polarity
D. They should have the same kVA rating
Which one is a reason why dust particles should never be allowed to accumulate on the windings and core on a dry-type transformer?
A. It will tend to corrode the metal surface
B. It will reduce dissipation of heat
C. It will absorb oil and grease
D. It may short circuit the windings
What type of core is used for a high frequency transformer?
A. Air core type
B. Silicon core type
C. Closed iron core type
D. Open iron core type
The all-day efficiency of a transformer is dependent on which of the following?
A. Its copper loss
B. The amount of load
C. The duration of load
D. Both B and C
Oil is invariably used in a large transformer for which of the following reasons?
A. To insulate the coils
B. To insulate the core
C. To lubricate the core
D. To lubricate the coils
In an autotransformer, how does the primary and secondary windings coupled?
A. Magnetically coupled only
B. Electrically coupled only
C. Both magnetically and electrically coupled
D. No coupling necessary
If the secondary of a transformer is stepped down, the primary will have ( ).
A. fewer turns
B. more turns
C. twice as many turns
D. half as many turns
What will happen to the eddy current loss of a transformer when its load is increased?
A. It will increase
B. It will decrease
C. It will remain the same
D. None of these
Which of the following can be altered by a transformer?
A. Frequency
B. Power
C. Demand factor
D. Voltage
What is the most common method of cooling a power transformer?
A. Natural air cooling
B. Forced-air cooling
C. Oil cooling
D. Special gas cooling
The core of a transformer are made from laminations of which of the following metal sheets?
A. Low carbon steel
B. Silicon steel
C. Chrome steel
D. Medium carbon steel
What is the reason why the transformer cores are laminated?
A. To simplify its construction
B. To minimize eddy current loss
C. To reduce the cost
D. To reduce the hysteresis loss
Which one is considered a main advantage of an autotransformer over a conventional two winding transformer?
A. Continuously varying voltage is available
B. Considerable saving in the winding materials
C. Copper losses are considerably reduced
D. Both A and B
In a three-phase Y-Y transformer connection, the neutral is fundamental to the ( ).
A. suppression of harmonics
B. provision of dual electric service
C. balancing of phase voltages with respect to line voltages
D. passage of unbalanced currents due to unbalanced loads
Which of the following can be determined with the open circuit test in a transformer?
A. Full load copper loss
B. Turns ratio
C. Rated power output at no load
D. Total equivalent impedance of the transformers
The savings in copper achieved by converting a two-winding transformer into an autotransformer is determined from which of the following?
A. Voltage transformation ratio
B. Load connected on the secondary
C. Size of the transformer core
D. Type of material used as the core
Which one is the biggest advantage of connection over the V-V connection for 3-phase power transformation?
A. It provides a set of balanced voltages under load
B. It provides a true 3-phase, 4-wire system
C. It provides a higher ratio of utilization
D. It provides more voltages
Which of the following is a determining factor for the reactance of the transformer?
A. Leakage flux
B. Mutual flux
C. Size of the core
D. Permeability of the core
What is the reason why the secondary of a current transformer is always short-circuited under operating conditions?
A. To protect the primary circuit
B. For safety purposes of the electricians
C. To avoid core saturation and high voltage induction
D. All of these
In a transformer, what is reason why the leakage flux of each winding is proportional to the current in that winding?
A. The leakage paths do not saturate
B. The two windings are electrically isolated
C. The mutual flux is confined in the core
D. Ohm's law applies to magnetic circuits
What is the reason why transformers have good all day efficiency?
A. Its copper loss is low
B. Its core loss is low
C. Its copper and core losses are both low
D. It is only loaded few hours in a given day
What is the effect of leakage flux in a transformer?
A. It will increase the copper loss
B. It will cause voltage drop in the windings
C. It will increase the eddy current loss
D. It will cause the life of the core to shorten
In a practical transformer, the copper loss is about what percent of the total loss?
A. 50%
B. 5%x
C. 1%
D. 85%
What is the function of the damper windings in a large alternator?
A. It will reduce voltage fluctuations
B. It will reduce frequency fluctuations
C. It will increase stability
D. None of these
The distribution of load between two alternators in parallel operation is changed using one of the following methods?
A. Change the driving torque of the prime movers
B. Change the frequency of the alternators
C. Change the phase sequence of the alternators
D. Change the excitation of the alternators
The drop in the terminal voltage of an alternator due to armature reaction is countered by which of the following?
A. Effect of saliency
B. Damper windings
C. Automatic voltage regulator
D. Increased prime mover output
After wiring two alternators, you checked the their frequency and voltage and found them to be equal. Before connecting them in parallel, which of the following should be the next one to be check?
A. Prime mover speed
B. Phase rotation
C. Steam pressure
D. Lubrication of rotor
The load sharing between two steam driven alternators operating in parallel are adjusted using which of the following methods?
A. Adjust steam supply to their prime movers
B. Adjust the power factors of the alternators
C. Adjust the speed of the alternators
D. Adjust the field strength of the alternators
When an alternator is supplying a zero leading pf load, the armature reaction will produce which of the following conditions?
A. Demagnetization of the main field flux
B. Magnetization of the main field flux
C. Cross magnetization of the main field flux
D. All of these
Which of the following prime mover types are used to drive salient-pole type alternators?
A. High speed prime mover only
B. Low speed prime mover only
C. Medium speed prime mover only
D. Both low and medium speed prime movers
What is the purpose of hydrogen in a large alternator?
A. To strengthen the magnetic field
B. To cool the alternator
C. To reduce the eddy current loss
D. To reduce distortion of the waveform
What is the purpose of a "reverse power relay"?
A. To reverse the rotation of a generator
B. To reverse the rotation of a motor
C. To protect the generator from a power reversal
D. To change AC to DC or DC to AC
Which of the following is not required in the parallel operation of alternators?
A. They must have the same terminal voltage
B. They must have the same phase rotation
C. They must have the same frequency
D. They must have equal ratings
Which of the following coils is the generated emf be more, for a given flux and number of turns?
A. Full pitch coil
B. Short pitch coil
C. Over pitch coil
D. All of these will generate equal emf
What is the reason why hydrogen is used for cooling of large size generators?
A. It is light
B. It offers reduced fire risk
C. It has high thermal conductivity
D . All of these
Which of the following is the type of rotor used in turbo alternators?
A. Small diameter and long axial length
B. Large diameter and long axial length
C. Same diameter and axial length
D. Large diameter and short axial length
To operate two or more alternators in parallel which of the following parameters must be identical?
A. Voltage
B. Frequency
C. Phase sequence
D. All of these
Two alternators A and B are operating in parallel and sharing equally a unity pf load. If the excitation of A is increased, which of the following will happen?
A. A will become lagging while B will become leading
B.A will become leading while B will become lagging
C. Both A and B will operate on leading pf
D. Both A and B will operate on lagging pf
In a big alternator, which one is the moving part?
A. Yoke
B. Poles
C. Armature
D. Commutator
At leading power factor, what is the effect of the armature flux of the alternator to its rotor flux?
A. It will aid
B. It will distort
C. It will oppose
D. It does not have any affect
What type of voltage is being applied to the field windings of an alternator?
A. High dc voltage
B. Low dc voltage
C. High ac voltage
D. Low ac voltage
In an alternator, what relationship is being shown in a magnetization curve?
A. Magnetic flux vs excitation current
B. Reactive power vs real power
C. Excitation current vs terminal voltage
D. Load current vs excitation current
Which of the following methods are commonly used in synchronizing alternators?
A. Dark lamp method only
B. Bright lamp method only
C. Dark lamp method and a synchroscope
D. Bright lamp method and a synchroscope
Pitch factor is defined as the ratio of the voltage induced in a ( ).
A. Full pitch coil to a short pitch coil
B. Short pitch coil to a full pitch coil
C. Short pitch coil to a long pitch coil
D. Long pitch coil to a short pitch coil
What will happen if a high speed alternator uses salient poles?
A. Reduced windage loss but excessive noise
B. Reduced windage loss and lesser noise
C. Excessive windage loss and excessive noise
D. Excessive windage loss but reduced noise
When two or more alternators are in parallel operation, their kW load share is changed by changing which of the following?
A. Driving torque
B. Excitation
C. Either A or B
D. Both A and B simultaneously
Two alternators A and B are operating in parallel. What will the operator do to transfer if in case he wish to transfer some loads of alternator A to alternator B?
A. Field current of alternator B must be increased
B. Field current of alternator B must be decreased
C. Speed of alternator B must be decreased
D. Prime mover power input of alternator B must be increased
Under no-load condition, the power drawn by the prime mover of an alternator goes to ( ).
A. produce power in the armature
B. produce induced emf in the armature
C. meet the no-load losses
D. meet the copper losses in both armature and rotor
Low speed alternators are driven by which of the following prime movers?
A. Steam turbines
B. Hydraulic turbines
C. Steam engines
D. Any of these
What is the reason why it is not adivasable to connect a stationary alternator to a live bus bars?
A. It will get short circuited
B. It will likely to run as a synchronous motor
C. It will cause the bus bar voltage to increase
D. It will disturb the generated emf of the other alternators connected in the bus
If the prime mover of an alternator supplying a load to an infinite bus is suddenly shut down what will happen to the alternator?
A. It will stop running
B. It will continue to run as an alternator
C. It will continue to run as a synchronous motor in the reverse direction
D. It will continue to run as a synchronous motor in the same direction
Alternators uses normally what type of field?
A. Rotating field type
B. Stationary field type
C. Either A or B
D. None of these D. None of these
When an alternator is supplying a zero lagging pf load, the armature reaction will produce which of the following conditions?
A . Demagnetization of the main field flux
B. Magnetization of the main field flux
C. Cross magnetization of the main field flux
D. All of these
Which of the following alternator parts plays an important role in over speed protection?
A. Circuit breaker
B. Overload relay
C. Governor
D. Differential protection
Which of the following types of rotors is best suitable for turbo alternators?
A. Salient pole type
B. Non-salient pole type or cylindrical rotor
C. Either A or B
D. None of these
In an alternator, which of the following is affected by armature reaction?
A. Driving speed of armature
B. Generated voltage per phase
C. Armature copper loss
D. Operating power factor
What is the usual connection of the armature windings of a three-phase alternator?
A. Delta
B. Wye
C. Wye-delta
D. Delta-wye
What will happen if an alternator designed for 60 Hz is operated at 50 Hz?
A. Its operating voltage will be derated to (50/60) of its original value
B. Its operating voltage will be derated to (50/60)² of its orginal value
C. Its kVA rating is upgraded to (60/50) of its rated value
C. Its kVA rating is upgraded to (60/50)² of its rated value
Which statement is true about an alternator operating at unity pf?
A. Generated emf is equal to the terminal emf
B. Generated emf is less than the terminal emf
C. Generated emf is more than the terminal emf
D. Either B or C, depending on how big is the load
A 3-phase alternator is running with a phase sequence of ABC for its three output voltages. If the direction of rotation is reversed, the phase sequence will become which of the following?
A. The same phase sequence of ABC
B. ACB sequence
C. CBA sequence
D. None of these
When an alternator connected to a bus bar is shut down, what happens to the bus bar voltage?
A. The voltage will decrease
B. The voltage will increase
C. The voltage will remain the same
D. The voltage will fall down to zero
When running under steady state conditions, which one represents the air gap field of the alternator?
A. It is stationary with respect to the stator
B. It is rotating at synchronous speed against the direction of rotor rotation
C. It is rotating at synchronous speed with respect to rotor
D. It is rotating at synchronous speed in the direction of rotor rotation
What do you mean by the phrase "synchronization" of alternators?
A. Connecting alternators in parallel
B. Adjusting excitation on alternators
C. Adjusting input torque on alternators
D. Running alternators at their synchronous speed
What is the size of an alternator in comparison to a dc generator, assuming they have the same power ratings?
A. The alternator is bigger in size
B. The alternator is smaller in size
C. Both machines have the same sizes
D. Either A, or B or C
When two or more alternators are in parallel operation, their KVAR load share is changed by changing which of the following?
A. Driving torque
B. Excitation
C. Either A or B
D. Both A and B simultaneously
A synchronous generator is connected to a power station. What will happen if the excitation is increased?
A. The reactive power generated will decrease
B. The reactive power generated will increase
C. The active power generated will increase
D. The active power generated will decrease
Which of the following refers to the synchronous reactance of the alternator?
A. Armature reactance and leakage reactance
B. A reactance connected in series with the alternator to reduce the fault current
C. It is the reactance of the field winding
D. It is the reactance of the winding at synchronous speed
What is the reason why the voltage regulation of an alternator is larger than the voltage regulation of a dc generator?
A. Due to large armature resistance
B. Due to large leakage reactance
C. Due to complex effect of the armature reaction
D. All of these
Salient rotor type for alternators are used in which of the following applications?
A. High speed prime mover is available
B. Low speed prime mover is available
C. Medium speed prime mover is available
D. Either B or C
An AC generator is run at 10% overload. What will happen?
A. No danger will occur
B. The brushes will spark excessively
C. The circuit breaker will kick out
D. The generator power factor will increase
In alternators, which type of protection is provided to protect against stator insulation failure?
A. Overcurrent relay
B. Reverse power relay
C. Differential protection
D. Thermocouple triggered alarm
What is the purpose of the frame of an alternator?
A. It is used to verticate the armature
B. It is used as a return path for the field flux
C. It is used to hold the armature stampings
D. It is used protect the operator of the machine
What is the purpose of using damper windings in alternators?
A. To prevent hunting
B. To achieve synchronism
C. To reduce friction and windage losses
D. To prevent the alternator from power reversal
In an alternator, the magnitude of the various voltage drops depends on which of the following?
A. Load current
B. Power factor of the load
C. Square of the load current
D. Power factor x load current
If the driving power from the prime mover driving the alternator is lost but the alternator remains connected to the bus bars with its field still excited, what will happen?
A. The alternator will run as a synchronous motor and will rotate in the same direction
B. The alternator will run as a synchronous motor and will rotate in the opposite direction
C. The alternator will still run as a synchronous generator but with less efficiency
D. The alternator will overload and get burn
The voltage regulation of an alternator is negative when the alternator is serving what type of load pf?
A. Zero pf
B. Unity pf
C. Leading pf
D. Lagging pf
