AC MACHINES 17

1. A distribution transformer should be selected on the basis of
a) efficiency
b) all day efficiency
c) voltage regulation
d) none of these
ans. b

2. In a transformer the iron losses do not vary with load current because
a) iron losses are equal to copy losses
b) core flux remain constant
c) core area is constant
d) none of these
ans. b

3. It is economical to use auto-transformer when the transformation ratio is
a) low
b) high
c) neither too high nor too low
d) none of these
ans. a

4. The no load test on a transformer is usually carried out by exciting the low voltage winding because
a) the required power input is low
b) the no load current becomes significant and can be conveniently measured
c) it is not advisable to work on the high voltage side
d) none of these
ans. b

5. During a short circuit test, the iron losses are negligible because
a) the mutual flux is small
b) the power factor is low
c) the current is high
d) none of these
ans. a

6. The transformer principle is based on
a) self-induction
b) mutual-induction
c) electric induction
d) the Lenz law
ans. b

7. Hysteresis loss in a transformer depends upon the
a) applied voltage
b) the type of core material
c) number of laminations
d) reactance of the winding
ans. b

8. What is the efficiency of transformers when compared with that of electrical motors of the same power ?
a) much smaller
b) somewhat smaller
c) about the same
d) much higher
ans. d

9. If in a transformer we double the secondary turns and at the same time reduce the primary voltage by half , then the secondary voltage will
a) he halved
b) be four times as high
c) not change
d) be doubled
ans. c

10. What type of core is used for a high frequency transformer?
a) open iron core
b) closed iron core
c) shell type iron core
d) air core
ans. d

AC MACHINES 16

1. Which of the following does not change in an ordinary transformer?
a) voltage
b) current
c) frequency
d) phase angle
ans. c

2. The color of fresh dielectric oil for a transformer is
a) pale yellow
b) dark brown
c) while grey
d) colourless
ans. a

3. In a transformer if in place of sine wave, a peaked voltage is fed to the primary,
a) the iron losses will be less
b) the iron losses will be more
c) the copper losses will be less
d) the noise level will be low
ans. a

4. The path of the magnetic flux in a transformer should have
a) low reluctance
b) low resistance
c) high reluctance
d) high resistance
ans. a

5. The function of breather in a transformer is
a) to filter the transformer oil
b) to provide oxygen to the cooling oil
c) to provide cooling air
d) to arrest the flow of moisture when outside air enters the transformer
ans. d

6. Transformer works on
a) ac only
b) dc only
c) both ac and dc
d) pulsating dc
ans. c

7. Iron losses in a transformer occur in
a) core
b) winding
c) insulating
d) main body
ans. a

8. Transformers use laminated core
a) to reduce eddy current loss
b) to reduce eddy current and hysteresis loss
c) to reduce copper loss
d) none of these
ans. a

9. In a transformer with closed magnetic coupling between primary and secondary windings.
a) efficiency will he high
b) all day efficiency will be high
c) regulation will be good
d) none of these
ans. c

10. The number of turns in the primary winding of a transformer depends on
a) input voltage
b) input current
c) both input voltage and current
d) none of these
ans. a

AC MACHINES 15

1. Current transformers for meters and relays usually have
a) 10-A secondaries
b) 5-A secondaries
c) 10:1 ratio
d) 1:1 ratio
ans. b

2. The main purpose of using an inter-phase transformer with a multi-anode rectifier is to
a) permit only one anode to fire at a time.
b) cause the anodes to overlap in firing.
c) shorten the period of firing of each anode.
d) act as an insulating transformer between the power transformer and load
ans. b

3. Dust should never be allowed to accumulate on the windings and are of a dry-type transformer because
a) may short-circuit the windings
b) tends to corrode metal surface
c) reduces dissipation of heat
d) absorbs oil and grease
ans. c

4. The relative polarity of the windings of a tranformer may be determined by
a) short-circuit test
b) open-circuit test
c) phasing out
d) back-to-back test
ans. c

5. The most common cause of contamination by water of oil used in transformers located indoors is
a) condensation of moisture from air in the upper part of the tank
b) decomposition of organic matter in the oil.
c) leaky bushings
d) use of filter blotters that have absorbed moisture from the air
ans. b

6. Part of the transformer which is most subject to damage from overheating is
a) winding insulation
b) frame or case
c) iron core
d) copper winding
ans. a

7. In general , the most important point to keep under constant watch during the operation of a transformers is its
a) primary voltage
b) core loss
c) exciting current
d) temperature
ans. d

8. The most essential feature of an auto-transformer is that it
a) is more suited for single-phase supply
b) is completely automatic in its operation
c) uses only one winding
d) none of the above
ans. c

9. When secondary of the transformer is loaded , the primary current will
a) not be effected
b) draw more current
c) draw less current than the secondary current
d) be the vector sum of no load current and excessive current drawn due to the secondary current.
ans. d

10  shell type transformer is commonly used because
a) it has more magnetic flux leakage
b) it has less magnetic flux leakage
c) it has two magnetic paths
d) both b and c are correct
ans. d

AC MACHINES 14

1.With increase in supply frequency of a transformer, there is
a) decrease in rating
b) increase in rating
c) no change in rating
d) none of these
ans. b

2. The essential condition for parallel operation of two single phase transformers is that they should have same
a) polarity
b) phase sequence
c) voltage ratio
d) percentage impedances
ans. a

3. Two transformers operating in parallel will share the load depending upon their
a) rating
b) leakage reactance
c) efficiency
d) per-unit impedance
ans. a

4. Which of the following method is used for cooling of transformer up-to a capacity of 10 MVA ?
a) oil natural cooling
b) Air blast cooling
c) Forced oil cooling
d) none of these
ans. a

5. Out of the following choices for polyphase transformer connections which one will you select for 3 to 2 phase conversion?
a) scott
b) star/star
c) double scott
d) star/double-delta
ans. a

6. When two identical transformers are available , then the best method to find their efficiency under load condition is
a) short-circuit test
b) back to back test
c) open-circuit
d) phase sequence test
ans. b

7. The open-circuit test on a transformer is meant for measuring its
a) copper losses
b) iron losses
c) insulation resistance
d) equivalent resistance
ans. b

8. Oil is invariably used in large transformers in order to
a) insulate the coils
b) insulate the core
c) lubricate the core
d) lubricate the coils
ans. a

9. The secondary winding if a current transformer whose primary is carrying current should
a) not be open circuited
b) not be short circuited
c) always be open circuited
d) not be connected to the current coil of a wattmeter
ans. a

10. Before disconnecting an ammeter from an energised current transformer circuit, the current tranformer
a) primary should be opened
b) secondary should be opened
c) primary should be shorted
d) secondary should be shorted
ans. d

AC MACHINES 13

1. In a transformer
a) both oc and sc tests are conducted on lv side.
b) oc test is conducted on hv and sc test is conduted on lv.
c) oc test is conducted on lv and sc test is conducted on hv.
d) both oc and sc test are conducted on hv side.
ans. c

2. For successful parallel operation of two single phase transformers, the essential condition is that their
a)  percentage impedances should be equal
b) turns ratios should be exactly equal
c) polarities must be properly connected
d) KVA ratings should be equal.
ans. c

3. In a single phase induction regulator, the output voltage can be varied
a) both in magnitude and phase
b) in magnitude only
c) in phase only
d) in magnitude less than the supply voltage
ans. b

4. Transformer action requires a
a) constant magnetic flux
b) increasing magnetic flux
c) pulsating magnetic flux
d) alternating electric flux
ans. c

5. In an oil filled transformer, oil is provided for
a) cooling
b) insulation
c) lubrication
d) both cooling and insulation
ans. d

6. Transformer cores are laminated to reduce
a) eddy current loss
b) hysteresis loss
c) both a and b
d) ohmic loss
ans. a

7. CRGO laminations in a transformer are used to minimise

a) eddy current loss
b) hysteresis loss
c) both a and b
d) ohmic loss
ans. b

8. An Air-core transformer, as compared to iron core transformer, has
a) less magnetic core loss
b) more magnetic core loss
c) no magnetic core loss
d) less ohmic loss
ans. c

9. Transformer zero voltage regulation occurs at
a) unity pf
b) leading pf
c) lagging pf
d) zero pf leading
ans. b

10. Transformer maximum efficiency, for a constant load current, occurs at
a) 0.8 pf
b) zero pf leading
c) zero pf lagging
d) unity power factor
ans. d

AC MACHINES 12

1. Winding to earth faults may be caused by
a) sludging of the oil
b) surge voltage only
c) current chopping only
d) both surge voltages and current chopping
ans. d

2. The two windings of a transformer are designated as
a) primary and secondary windings
b) primary and hv windings
c) secondary and lv windings
d) hv and lv windings
ans. d

3. The flux involved in the emf equation of a transformer has
a) rms value
b) average value
c) total value
d) maximum value
ans. d

4. The leakage flux in a transformer depends upon
a) the applied voltage
b) the frequency
c) the load current
d) the mutual flux
ans. c

5. Good voltage regulation of a transformer means that the difference between its no-load  voltage and full-load voltage is
a) very high
b) low
c) very low
d) none of these
ans. d

6. Distribution transformers have core losses
a) greater than copper losses
b) equal to copper losses
c) less than copper losses
d) equal to 1/2 (copper losses)
ans. c

7. Eddy current loss in a transformer depends on
a) both voltage and frequency
b) voltage alone
c) load current alone
d) thickness of core
ans. d

8. Hysteresis loss in a transformer depends upon
a) frequency
b) supply voltage
c) square of the frequency alone
d) square of the voltage alone
ans. a

9. The open-circuit test on transformer is conducted to obtain
a) the leakage impedances
b) the ohmic loss
c) hysteresis loss only
d) core losses
ans. d

10. The short-circuit test on a transformer is conducted to obtain
a) core losses at any load
b) ohmic losses at any load
c) hysteresis losses
d) both core and ohmic losses
ans. b

AC MACHINES 11

1. A transformer may have two or more ratings depending on
a) the type of winding used
b) the type of cooling used
c) the type of core used
d) the type of insulation used
ans. b

2. Conservator is used
a) to take up the expansion of oil due to temperature rise.
b) to act as an oil storage
c) for better cooling of the transformer
d) none of these
ans. a

3. Buchholz relay is placed
a) in between the conservator and the breathe
b) in between the tank and the conservator
c) in between the h.v. winding and the bushing
d) in between the l.v.winding and the bushing
ans. b

4. Buchholz relay is a
a) voltage sensitive device
b) current sensitive device
c) frequency sensitive device
d) gas actuated device
ans. d

5. Buchholz relay causes
a) tripping for major fault and alarm for minor faults
b) alarm for major fault and tripping for minor faults
c) tripping for both major and minor faults
d) alarm for both major and minor faults
ans. a

6. Transformer oil is used as
a) insulant only
b) coolant only
c) both insulant and coolant
d) insert medium
ans. c

7. Sludging of transformer oil means
a) continuous expansion and contraction due to heating and cooling
b) formation of semi-solid hydro-carbon due to heat and oxidation
c) decomposition of transformer oil under the influence of power arcs
d) evaporation of transformer oil due to heating
ans. b

8. To avoid breakdown of transformers under surges any one of the following except one may be adopted
a) use of surge absorbers
b) use of surge diverters
c) use of metal shields
d) Reinforcement to end-turn insulation.
ans. d

9. Repeated switching of transformers located nearer the generating station may cause
a) surface flashover of the bushings
b) mechanical distortion of the windings and subsequent turn to turn insulation failure
c) excessive temperature rise
d) intense local eddy currents in the core
ans. b

10. If the drying out operation of a transformer is unduly shortened and normal voltage is applied, then there is possibility of
a) inter-turn failure
b) winding to earth failure
c) terminal to terminal flashover
d) excessive overheating of the transformer
ans. a

AC MACHINES 10

1. For cold rolled grain-oriented silicon steel metered overlap is preferable for the core-yoke joint as
a) it improves mechanical strength
b) it makes better use of core space
c) it reduces magnetostriction
d) it reduces magnetizing current and also the core-losses
ans. d

2. The direction of central phase winding of a three-phase shell type transformer is reversed with respect to the outer phases to
a) save considerable amount of core material
b) reduce leakage fluxes
c) reduce short circuit forces
d) minimise eddy current loss
ans. a

3. Low voltage windings are placed nearer to the core in the case of concentric windings because it reduces
a) hysteresis loss
b) eddy current loss
c) insulation requirement
d) leakage fluxes
ans. c

4. Spiral winding is suitable only for windings
a) carrying very low current
b) carrying very high current
c) rated for high voltage
d) rated for low voltage
ans. b

5. Helical winding is suitable for
a) low voltage winding of small transformers
b) high voltage winding of small transformers
c) low voltage winding of large transformers
d) high voltage winding of large transformers
ans. c

6. Cross over winding is suitable for
a) low voltage winding of small transformers
b) high voltage winding of small transformers
c) low voltage winding of large transformers
d) high voltage winding of large transformers
ans. c

7. Continuous disc winding is suitable for
a) low voltage winding of small transformers
b) high voltage winding of small transformers
c) low voltage winding of large transformers
d) high voltage winding of large transformers
ans.d

8. In general , for all sizes of distribution transformer, it is preferable to use
a) plain sheet steel tanks
b) tubed tanks
c) corrugated tanks
d) radiator tanks
ans. b

9. For small power transformers, it is preferable to use
a) tubed tanks
b) corrugated tanks
c) radiator tanks
d) tanks with separate coolers
ans. a

10. For large power transformer, it is preferable to use

a) tubed tanks
b) corrugated tanks
c) radiator tanks
d) tanks with separate coolers
ans. d

AC MACHINES 9

1. While conducting short-circuit test on a transformer the following side is short-circuited
a) HV side
b) LV side
c) Primary side
d) none of these
ans. b

2. The secondary of a current transformer is always short circuited under operating conditions because
a) it protects the primary circuits
b) it is safer to human beings
c) it avoids core saturation and high voltage induction
d) none of these
ans. c

3. Two transformers operating in parallel will share the load depending upon their
a) ratings
b) leakage reactance
c) efficiency
d) p.u. impedance
ans. a

4. Iron losses of a transformer can be calculated by knowing the weights of
a) cores only
b) yokes only
c) copper winding only
d) cores and yokes
ans. d

5. With the increase in supply frequency of a transformer there is
a) decrease in rating
b) increase in rating
c) no change in rating
d) none of these
ans. b

6. Silicon steel is preferred for transformer core because
a) it decrease the permeability of the core
b) it reduces both eddy current loss and hysteresis loss
c) it reduces resistivity of the core
d) it decreases the tensile strength
ans. b

7. The magnetic properties of silicon steel crystal are best
a) along the cube edges
b) along the surface diagonals
c) along the cubic diagonals
d) none of the above
ans. a

8. The magnetic properties of cold rolled grain oriented silicon steel are excellent
a) against the direction of rolling
b) at the right angles to the direction of rolling
c) along the direction of rolling
d) none of these
ans. c

9. For large power transformer the best utilisation of available core space can be made by using
a) rectangular core section
b) square core section
c) stepped core section
d) none of the these
ans. c

10. Five limb core construction has an advantage over the three limb core construction that
a) the eddy current loss is less
b) the magnetic reluctance of the three phases can be balanced
c) the hysteresis loss is less
d) the permeability is higher
ans. b

AC MACHINES 8

1. The main purpose of performing open circuit test at rated voltage is to measure
a) copper loss
b) core loss
c) total loss
d) insulation resistance
ans. b

2. The short-circuit test in a transformer is used to determine
a) iron loss at any load
b) copper loss at any load
c) hysteresis loss
d) eddy-current loss
ans. b

3. The commercial efficiency of a transformer while on open-circuit is
a) zero
b) maximum
c) either zero or 100 %
d) none of these
ans. a

4. An ideal power transformer will have maximum efficiency at a load such that
a) copper loss is less than iron loss
b) copper loss is equal to  iron loss
c) copper loss is higher than iron loss
d) none of these
ans. b

5. The iron-losses of a transformer can be calculated by knowing the weights of
a) core only
b) yokes only
c) copper winding only
d) cores and yokes
ans. d

6. With the increase in supply frequency of a transformer, there is
a) decrease in rating
b) increase in rating
c) no change in rating
d) none of these
ans. b

7. The ordinary efficiency of a given transformer is maximum when
a) it runs at half full-load
b) it runs at full-load
c) its copper loss equals iron loss
d) it runs overload
ans. c

8. In a transformer, the resistance between its primary and secondary  should be
a) infinity
b) zero
c) 500 ohms
d) nearly 1 k
ans. a

9. The main purpose of using core in a transformer is to
a) decrease iron losses
b) prevent eddy current loss
c) eliminate magnetic hysteresis
d) decrease reluctance of the common magnetic flux path
ans. d

10. The transformer cores are laminated in order to
a) simplify its construction
b) minimize eddy current loss
c) reduce cost
d) reduce hysteresis loss
ans. b

AC MACHINES 7

1. For a given application , the transformation ratio of a transformer
a) is fixed but not constant
b) is constant but not fixed
c) is dependent on secondary load
d) depends on which winding is used as primary
ans. a

2. Two transformers when operating in parallel will share the load depending upon their
a) magnetizing current
b) leakage current
c) per unit impedance
d) efficiency
ans. c

3. Ferrite cores are used in high frequency transformer because it has
a) low permeability
b) high hysteresis
c) low resistance
d) high resistance
ans. d

4. The size of transformer core will depend on
a) frequency
b) flux density of the core material
c) area of the core
d) both A and B current
ans. d

5. Two transformers operating in parallel will share the load depending upon their
a) efficiency also
b) ratings also
c) leakage reactance
d) none of these
ans. b

6. In a transformer the purpose of breather is to
a) extract moisture from the air
b) to take insulating oil form the conservator
c) to provide cooling to the winding
d) to provide insulation to the winding
ans. a

7. Conservator consists of
a) an air-tight metal drum fixed at the top of the tank
b) drum placed at the bottom of the tank
c) overload protection
d) none of these
ans. a

8. The nominal short-circuit voltage of the transformer is defined as the precentage of
a) the test voltage
b) the rated secondary voltage
c) the rated primary voltage
d) the nominal transformation ratio
ans. c

9. The efficiency in transformer is maximum at
a) full load
b) half the full load
c) one third the full load
d) no load
ans. a

10. No-load test on a transformer is carried out to determine
a) copper loss
b) full-load current
c) magnetizing current
d) efficiency of the transformer
ans. c

AC MACHINES 6

1. A transformer is working at its maximum efficiency. Its iron-loss is 500 W. Its copper-loss will be
a) 250 W
b) 300 W
c) 400 W
d) 500 W
ans. d

2. Distribution transformers are designed to have maximum efficiency nearly
a) at full load
b) at 50% of FL
c) at no load
d) none of these
ans. b

3. Distribution transformers have good all day efficiency due to
a) low copper-loss
b) low iron loss
c) low copper as well as iron losses
d) none of these
ans. b

4. The special silicon steel is used for lamination's because
a) eddy current losses are induced
b) hysteresis losses are reduced
c) both losses are reduced
d) none of these
ans. b

5. The yoke sections of transformers using hot-rolled lamination's is made 15% greater than that of the core so as to
a) to reduce the copper-loss
b) to increase the size of transformers
c) to reduce the iron loss in yoke and magnetizing current
d) to provide better cooling
ans. c

6. The concentric windings are used in core-type transformers with
a) HT winding placed next to core
b) LT winding placed next to core
c) LT winding on the outer side
d) HT winding on the outer side
ans. b

7. In power transformers the tapping's are provided on
a) high voltage side
b) low voltage side
c) in the middle of both windings
d) LV as well as on HV side
ans. a

8. The advantage of putting tappings at the phase ends of transformer is
a) to obtain fine variation of voltage
b) to operate with ease
c) to obtain better regulation
d) reduce the number of bushings
ans. d

9. Transformer transforms
a) frequency
b) voltage
c) current
d) power
ans. b

10. A step-up transformer increases
a) voltage
b) current
c) power
d) frequency
ans. a

AC MACHINES 5

1. Why there is an enamel layer coated over the lamination of the transformer core?
a) To decrease the hum
b) To attain adhesion between the lamination
c) To insulate the laminations against each other
d) To prevent the corrosion of the laminations.
ans. c

2. What is the efficiency of transformer compared with that of electrical motors of the same power?
a) Much smaller
b) Some what smaller
c) About the same
d) Much higher
ans. d

3. According to the name plate of a small transformer, the secondary normal voltage is 220 V. Which of the following statements about it is true?
a) The no-load voltage is more than 220V.
b) 220V is the no-load voltage.
c) At a load which draws the rated current, the voltage becomes less than 220 V
d) The secondary voltage increases with increasing load.
ans. a

4. Upon which factor does the short circuit voltage of a transformer mainly depend. It depends
a) on the ohmic resistance of the primary winding
b) on the ohmic resistance of the secondary winding
c) on the cross-sectional area of their core
d) on the magnitude of the leakage flux
ans. d

5. Which of the following statements about a transformer having a small short circuit voltage is true?
a) The transformation ratio of the transformer is small
b) During the operation the transformer has high iron losses
c) During operation the transformer has high copper losses
d) A high short circuit current flows through the transformer.
ans. d

6. What is the typical use of an auto-transformer?
a) Isolating transformer
b) Toy transformer
c) Control transformer
d) Variable transformer
ans.d

7. In any transformer, the voltage per turn in primary and secondary remains
a) always same
b) always in ratio of K
c) always different
d) sometimes same.
ans. a

8. In any single phase transformer, the primary and secondary induced voltages are
a) 180 degrees out of phase
b) 90 degrees out of phase
c) in phase
d) none of these
ans. c

9. The no load current taken by actual transformer lags the applied voltage by
a) 80 degrees
b) 60 degrees
c) 50 degrees
d) 30 degrees
ans. a

10. The full load copper-loss in a transformer is 400 W. At half load, the copper-loss will be
a) 400 W
b) 200 W
c) 100 W
d) 50 W
ans. c

AC MACHINES 4

1. What type of core is used for a high frequency transformer?
a) open iron core
b) air core
c) closed iron core
d) none of these
ans. b

2. Which of the statements given below is true for the auto transformer?
a) It has to separate windings connected in series externally
b) it has only one winding
c) it can only step down the voltage
d) it is most suitable for power transformation
ans.b

3. The self induced voltage of a coil depends upon
a) the voltage applied to the coil
b) the shape of the iron core
c) the shape of the bobbin
d) the number of turns of the coil
ans. d

4. Which of the following is a correct statement about eddy currents?
a) Eddy currents improve the efficiency of a motor
b) Eddy currents heat up the copper winding
c) Eddy currents heat up the metal parts
d) Eddy currents are used for arc welding.
ans. c

5. The use of higher flux density in transformer design
a) increases the weight per kVA
b) decreases the weight per kVA
c) increases the weight per kW
d) decreases the weight per kW
ans. b

6. The transformer oil used in transformers provides
a) insulation and cooling
b) cooling and lubrication
c) insulation and lubrication
d) insulation ,cooling and lubrication
ans. a

7. The induced emf in the secondary of a transformer will depend on
a) frequency of the supply only
b) number of turns in secondary only
c) maximum flux in the core only
d) frequency , flux and number of turns in the secondary .
ans. d

8. A transformer has a turns ratio of 1 to 10 and a resistance of 5000 ohms is connected across the secondary terminals, the resistance offered to a current flowing in the primary will be
a) 50 ohms
b) 500 ohms
c) 5000 ohms
d) 50 kilo ohms
ans. a

9. Two transformers are operating in parallel, they will share the load depending upon their
a) efficiency
b) ratings
c) leakage reactance
d) per-unit impedance
ans. d

10. Which of the following statements about a short-circuit power transformer is true?
a) There is a fuse in its primary circuit
b) There is a bimetallic switch in its primary circuit
c) There is a fast magnetic switch in its primary circuit
d) The short-circuit current can continuously flow through it without causing a damage
ans. d

AC MACHINES 3

1. Which of the following is a correct statement about eddy current?
a) Eddy currents improve the efficiency of a motor.
b) Eddy currents do not influence the movement.
c) Eddy current heat up the metal parts
d) Eddy currents are used for are welding.
ans. c

2. The steel for construction of transformer core is made to have
a) high permeability and low hysteresis loss
b) low permeability and high hysteresis loss
c) low permeability and low hysteresis loss
d) high permeability and high hysteresis loss
ans. a

3. As compared to an amplifier , a transformer cannot
a) increase the output voltage
b) increase the output current
c) increase output power
d) none of these
ans. c

4. In an ideal transformer on no-load, the primary applied voltage is balanced by
a) the secondary voltage
b) the drop across resistances and reactance
c) the secondary induced emf
d) the primary induced emf
ans. c

5. A sinusoidal emf
a) lags the flux inducing it by 180 degrees
a) lags the flux inducing it by 90 degrees
a) leads the flux inducing it by 90 degrees
a) leads the flux inducing it by 180 degrees
ans. b

6. The magnitude of mutual flux in a transformer is
a) low at low loads and high and high loads
b) high at low loads and low at high loads
c) same at all loads
d) varies at low loads and constant at high loads
ans. c

7. At every instant the direction of secondary current in a transformer must be such as to oppose any change in flux . This is in accordance with
a) Faraday's laws
b) Joule's law
c) Lenz's law
d) Coulomb's law
ans. c

8. If in a transformer the secondary turns are doubled at the same time the primary voltage is reduced by half, then the secondary voltage will
a) be halved
b) be four times as high
c) not change
d) be reduced to quarter
ans. c

9. Transformers are rated in
a) kw
b) kV
c) kWh
d) kVA
ans. d

10. Which is the common method of cooling a power transformer ?
a) Air-cooling
b) Air-blast cooling
c) Oil cooling
d) natural cooling
ans. c

AC MACHINES 2

1. If lower voltage is given to the primary and higher voltage is taken from the secondary of a transformer, it is called
a) step up
b) step down
c) current transformer
d) voltage stabilizer
ans. a

2. If the input voltage is 100 V and output voltage is 200 V, which side of the transformer winding's will be primary
a) 200 V side
b) 100 V side
c) Winding with more turns
d) Winding with less turns.
ans. d

3. Shell-type transformer is commonly used because
a) it has more magnetic flux leakage
b) it has less magnetic flux leakage
c) it has two magnetic paths
d) both b and c are correct
ans. d

4. The transformer is commonly used because
a) it has high efficiency
b) frequency remains constant
c) construction cost per kVA is less as compared to other machines
d) All of these
ans. d

5. The emf induced in the secondary winding depends upon
a) number of turns
b) flux
c) supply frequency
d) all of these
ans. d

6. When the secondary of the transformer is loaded , the flux in the transformer will
a) remain constant
b) directly proportional to secondary current
c) directly proportional to the current drawn by primary winding
d) none of these
ans. a

7. When secondary of the transformer is loaded , the current in the primary side will
a) not be effected
b) increase
c) decrease
d) be the sum of no-load current and excessive current drawn due to secondary current.
ans. d

8. Electric power is transferred from one coil to the other coil in a transformer
a) electrically
b) electromagnetically
c) magnetically
d) physically
ans. c

9. A transformer operates
a) always at unity power factor
b) has its own power factor
c) at a power factor below a particular value
d) at power factor depending on the power factor of the load
ans. d

10. The lamination's are made from
a) silicon sheet steel
b) nickel alloy steel stamping
c) low carbon steel
d) chrome steel sheets
ans. a

AC MACHINES

1. Transformer is used to change the values of
a) voltage
b) frequency
c) power
d) power factor
ans. a

2. The path of the magnetic flux in a transformer has
a) high reluctance
b) low resistance
c) high conductivity
d) low reluctance
ans. d

3. Transformer is a
a) Rotating device
b) Static device
c) Magnetic device
d) none of the above
ans. b

4. Transformer works on
a) a.c
b) d.c
c) a.c and d.c both
d) pulsating d.c
ans. a

5. Transformer works on the principle of
a) self-induction
b) mutual induction
c) Faraday's  law of electro magnetic induction
d) self and mutual induction both
ans. d

6. Transformer is device which transform the voltage
a) from higher level to lower level
b) from lower level to higher level
c) both a and b
d) none of these
ans. c

7. If d.c supply is given to a transformer it may
a) work
b) not work
c) give lower voltage than the rated voltage on secondary side
d) burn the winding
ans.d

8. Different types of transformers are
a) core type
b) shell type
c) berry type
d) All the these
ans. d

9. Rating of transformer is given in
a) kVA
b) kVAR
c) kW
d) Watts
ans. a

10. If a higher voltage is given to the primary and low voltage is taken from the secondary of transformer it is called
a) step-up
b) step-down
c) instrument transformer
d) stabilizer
ans. b