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Multiple choice question for engineering

Set 1

1.How many types are the current transformers classified into?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] The current transformers are classified into 2 types. They are wound type and bar type.

2. What is the wound type current transformer?
a) primary winding having one full turn wound on core
b) primary winding having more than one full turn wound on core
c) secondary winding having one full turn wound on core
d) secondary winding having more than one full turn wound on core

View Answer

Answer: b [Reason:] The wound type current transformer is one of the classifications of the current transformers. The primary winding has more than one full turn wound on core.

3. What is the bar type current transformer?
a) primary winding consists of a rod of suitable size and material
b) primary winding consists of a bar of suitable size and material
c) secondary winding consists of a rod of suitable size and material
d) secondary winding consists of a bar of suitable size and material

View Answer

Answer: b [Reason:] The bar type current transformer is one of the classifications of the current transformers. In bar type winding, primary winding consists of a bar of suitable size and material.

4.How many commonly used shapes of current transformer are present?
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: c [Reason:] The current transformers consists of 3 commonly used shapes. They are stadium, circular, rectangular orifices.

5. What material is made use of for the lamination in the current transformer?
a) cold rolled steels
b) hot rolled steels
c) copper
d) hot iron

View Answer

Answer: b [Reason:] The current transformer consists of stacks of laminations. The lamination used in the current transformer is hot rolled steel.

6. What is the insulation material used in the current transformer?
a) elephantide
b) presspahn
c) elephantide and presspahn
d) elephantide or presspahn

View Answer

Answer: d [Reason:] The insulation in current transformer is by means of end collars and circumferential wraps. The insulation material used in elephantide or presspahn.

7. What is the additional usage of the presspahn material used as insulation material?
a) lamination
b) to reduce the losses
c) to protect secondary winding conductor from mechanical damage
d) to protect secondary winding conductor from electrical damage

View Answer

Answer: c [Reason:] The presspahn is used as insulating material in the current transformer. In addition to that the presspahn is also used to protect the secondary winding conductor from mechanical damage.

8. What is the other name of the ring type current transformer?
a) brush transformer
b) cloud transformer
c) circular transformer
d) bushing transformer

View Answer

Answer: d [Reason:] The ring type current transformer is one type of current transformer. It is also known as the bushing transformer.

9.How many faces are present in the split core current transformer?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] The split core transformer consists of a split core. The split half consists of 2 finely grounded or lapped gap faces.

10. The current transformers are assembled on to the secondary conductors “on site” for either permanent or temporary duty?
a) true
b) false

View Answer

Answer: b [Reason:] The current transformers are assembled on to the primary conductors. They are assembled “on site” for the permanent or temporary duty.

11. What is the insulation material on the primary conductor?
a) bakelized paper tube
b) resin
c) bakelized paper tube and resin
d) bakelized paper tube or resin

View Answer

Answer: d [Reason:] The insulation material on the primary conductors is generally made up of the bakelized paper tube. It can also be made use of resin directly moulded on the bar.

12. How is the reluctance of the interleaved corner related with the magnetizing current?
a) reluctance of the interleaved corner is directly proportional to the magnetizing current
b) reluctance of the interleaved corner is indirectly proportional to the magnetizing current
c) reluctance of the interleaved corner is directly proportional to the square of the magnetizing current
d) reluctance of the interleaved corner is indirectly proportional to the square of the magnetizing current

View Answer

Answer: a [Reason:] The reluctance of the interleaved corner is directly proportional to the magnetizing current. As the reluctance is being reduced it in turn reduces the magnetizing current.

13. To reduce the peak voltage between layers, the secondary winding is being sectionalized?
a) true
b) false

View Answer

Answer: a [Reason:] The large number of secondary turns requiring more than 1 winding layer, the secondary winding is sectionalized. This is because to reduce the peak voltage between layers.

Set 2

1. How many type of armature windings are present in the DC machine armature?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] There are basically two types of armature windings present. They are known as lap winding and wave winding.

2. Which factor determines the difference between the types of armature windings?
a) brush connection
b) slip ring connection
c) commutator connection
d) pole connection

View Answer

Answer: c [Reason:] The armature windings are all connected to the commutator in the case of DC machines. Commutator is nothing but device which converts dc voltage to ac voltage.

3. What is the meaning of pole pitch?
a) type of armature slot
b) number of armature slots/pole
c) number of poles/armature slot
d) number of poles/number of armature slots

View Answer

Answer: b [Reason:] Pole pitch is the concept which is used in the armature slot design. It is nothing but the ratio between the number of armature slots present to the number of poles used in the machine design.

4. A 4 pole DC machine has 36 number of armature conductors. What is the pole pitch ?
a) 9
b) 1/9
c) 92
d) 1/92

View Answer

Answer: a [Reason:] Pole pitch = Number of armature slots/pole Pole Pitch = 36/4 =9.

5. The choosing of the slot values for armature depends on the type of windings?
a) true
b) false

View Answer

Answer: a [Reason:] The slot values are chosen based on the type of windings. If wave winding is used, then multiples of pole pair is chosen as slot values and if lap windings are used the slot values are continuous and not multiples of pole pair.

6. What is the condition for choosing the armature current/parallel path in armature design?
a) > 200 ampere for both lap and wave windings
b) >200 ampere for lap winding, <200 ampere for wave winding
c) < 200 ampere for both lap and wave windings
d) <200 ampere for lap winding, >200 ampere for wave winding

View Answer

Answer: c [Reason:] While designing the armature slots, the armature current should be less than 200 ampere. The armature current should also never cross 200 ampere for the lap winding.

7. What is the range of armature slot pitch in the armature slot design?
a) 20mm – 25mm
b) 25mm – 35mm
c) 30mm – 35mm
d) > 35mm

View Answer

Answer: b [Reason:] For the armature design, the lowest value of slot pitch is generally chosen as 25mm. The highest value of slot pitch is generally chosen as 35mm.

8. For a DC machine, the armature slot pitch is 35mm and the diameter is 0.2m. What is the number of armature slots for the machine?
a) 17
b) 18
c) 19
d) 20

View Answer

Answer: b [Reason:] Number of armature slots = (3.14*D)/Number of armature slot pitch Number of armature slots= (3.14*0.2)/35*10-3 Number of armature slots= 17.94 = 18(approx).

9. What is the formula to reduce flux pulsations?
a) armature slot/number of poles = integer
b) armature slot/number of poles = integer + 0.5
c) armature slot/number of poles = integer – 0.5
d) armature slot/number of poles = integer +-0.5

View Answer

Answer: d [Reason:] First the number of armature slots is calculated. Then the ratio of the number of armature slots to the number of poles is approximately equal to integer+-0.5.

10. The number of coils chosen should be minimum in number?
a) true
b) false

View Answer

Answer: a [Reason:] The number of coils chosen for the armature slot design should always be minimum in number. This is because the machine cost reduces and it becomes cost efficient.

11. What should be the range of the integer value while calculating the formula to reduce the flux pulsations?
a) 8-14
b) 9-15
c) 9-16
d) 9-17

View Answer

Answer: c [Reason:] While calculating the formula to reduce the flux pulsations, the lowest value is generally chosen as 9. The highest value of integer chosen is generally 16.

12. What is ‘Z/Sa’ calculation during design of armatures?
a) armature poles/slots
b) armature conductors/slots
c) armature slots/poles
d) armature slots/conductors

View Answer

Answer: b [Reason:] This is the second step in the armature design. Firstly, the number of armature conductors is found out. Then the number of slots used is taken and the ratio of both gives the value of ‘Z/Sa’.

13. What is the formula for calculating the minimum number of coils?
a) Cmin = Voltage
b) Cmin = Voltage/5
c) Cmin = Voltage/10
d) Cmin = Voltage/15

View Answer

Answer: d [Reason:] The voltage through the armature is first calculated from the data given. Then the value of voltage is divided by 15,to get the value of minimum number of coils.

14. Given Z=228 conductors, number of coils C=38 for a DC machine. What is the turns/coils ratio?
a) 4
b) 3
c) 7
d) 3

View Answer

Answer: d [Reason:] Turns/coils = Number of armature conductors/(2*Number of coils) Turns/coils= 228/38*2 = 3.

15. For a DC generator, given the load current is 510 ampere, field current is 1.4 ampere. What is the value of armature current?
a) 508.6 ampere
b) 714 ampere
c) 511.4 ampere
d) 364.28 ampere

View Answer

Answer: c [Reason:] For DC generator, Armature Current= Load Current + Field Current Armature Current= 510 + 1.4 = 511.4 ampere.

Set 3

1. What is a commutator in DC machines?
a) electrical device which reverses the current direction between the rotor and external circuit
b) mechanical device which reverses the current direction between the rotor and external circuit
c) electrical device which allows the current flow between the rotor and external circuit
d) mechanical device which allows the current flow between the rotor and external circuit

View Answer

Answer: a [Reason:] Commutator is an electrical device found only in DC machines. It is used to reverse the current direction between rotor and external circuit. It also changes dc voltage to alternating voltage.

2. What is the use of brushes in DC machines?
a) to connect the parts of the machine to the external circuit
b) to conduct current between moving parts
c) to conduct current between stationary wires and moving parts
d) used for smooth conduction of current

View Answer

Answer: c [Reason:] Brushes are another important part in the construction of DC machine. They are connected in the lower end of the machine to allow the current flow between the moving parts and stationary wires.

3. Which material is commonly used in brushes?
a) copper
b) carbon
c) silicon
d) steel

View Answer

Answer: b [Reason:] Carbon is the most commonly used material in the manufacture of brushes. It is because carbon has high melting point, and is also less prone to high temperatures.

4. What is the total number of design steps available for the commutators in DC machines?
a) 4
b) 3
c) 2
d) 5

View Answer

Answer: a [Reason:] There are basically 4 design steps available for the commutators. They include the finding of the number of commutator segments, voltage across the commutator, width of the commutator and length of the commutator.

5. What is the total number of design steps for the brushes in DC machines?
a) 4
b) 3
c) 5
d) 6

View Answer

Answer: c [Reason:] There are basically 5 steps in the brush design. They include the calculation of the brush current, number of brushes, thickness of the brush, width of the brush, total commutator losses.

6. What factor does the diameter of the commutator depends on?
a) length of the commutator
b) speed of the commutator
c) peripheral speed of the commutator
d) opening of the commutator

View Answer

Answer: c [Reason:] Peripheral speed is a term which is used in the design of the commutators of DC machines. If the peripheral speed of the machine gets crossed, then the diameter should be reduced.

7. For a DC machine, given Diameter of the commutator= 0.48 m, Speed = 600 rpm. What is the voltage across the commutator?
a) 15 V
b) 15.5 V
c) 15.2 V
d) 15.1 V

View Answer

Answer: d [Reason:] Voltage across the commutator = 3.14*(Diameter of the commutator)*Speed Voltage = 3.14*0.48*600 = 15.1 V.

8. What is the other name for commutator segment pitch of DC machines?
a) width of the commutator
b) length of the commutator
c) breadth of the commutator
d) height of the commutator

View Answer

Answer: a [Reason:] Commutator segment pitch is otherwise known as the width of the commutator. It is one of the commutator design steps.

9. What is the formula for finding out the width of the commutator of the DC machines?
a) width of the commutator = 3.14*(Diameter of the commutator)
b) width of the commutator = 3.14*(Diameter of the commutator)*(Number of armature coils)
c) width of the commutator = 3.14*(Diameter of the commutator) / (Number of armature coils)
d) width of the commutator = Number of armature coils / 3.14*(Diameter of the commutator)

View Answer

Answer: c [Reason:] First by the design of the armature, the number of armature coils is found out. Then the diameter of the commutator is measured.

10. The diameter of the commutator should be 0.2-0.4 times the main diameter for a good design?
a) true
b) false

View Answer

Answer: b [Reason:] For a good design of the commutator, the diameter of the commutator should be in the range of 0.6-0.8 times of the main diameter. If the value goes above or below this range, we should not choose that value.

11. What should be the range for the width of the commutator in a good design?
a) < 4 mm
b) > 4 mm
c) 3-4 mm
d) < 3 mm

View Answer

Answer: b [Reason:] For a good design of the commutator, the width of the commutator should be greater than 4 mm. If the value goes below 4 mm, we should not choose that value.

12. The design of commutator and the brushes of DC machines are interconnected?
a) true
b) false

View Answer

Answer: a [Reason:] The design of brushes and commutators are interconnected, because in the calculation of the length of the commutator, the width of the brush, number of brushes are used. In the same way, brush values are also used in calculation of commutator loss.

13. What is the formula for calculation of brush current of DC machine for wave winding?
a) brush Current = 2*(Armature Current) / P
b) brush Current = (Armature Current) / P
c) brush Current = Armature Current
d) brush Current = P/2*(Armature Current)

View Answer

Answer: c [Reason:] Brush Current = 2*(Armature Current) / P is the formula for the calculation of brush current of DC machine for lap winding.

14. What is the formula for brush contact loss of DC machines?
a) brush contact loss = armature current + brush contact voltage
b) brush contact loss = armature current – brush contact voltage
c) brush contact loss = armature current * brush contact voltage
d) brush contact loss = (armature current + brush contact voltage) / 2

View Answer

Answer: c [Reason:] For calculation of the brush contact loss, first the armature current is obtained. Then the voltage through the brush contacts is calculated and the product gives the brush contact loss.

15. What is the formula for total commutator loss for DC machine?
a) brush contact loss + brush friction loss
b) brush contact loss – brush friction loss
c) brush contact loss * brush friction loss
d) brush contact loss / brush friction loss

View Answer

Answer: a [Reason:] Brush contact loss = brush contact loss = armature current * brush contact voltage Brush friction loss = (Coefficient f friction)*Brush Pressure*Area of the brush*Commutator voltage.

Set 4

1. What is stacking factor?
a) the allowance made for the power loss
b) the allowance made for the space loss between laminations
c) the allowance made for the heat loss between laminations
d) the allowance made for the power loss between laminations

View Answer

Answer: b [Reason:] The net cross sectional area is obtained from the dimensions of various packets and an allowance is made for the space lost between laminations. This allowance is called stacking factor.

2. What is utilization factor?
a) utilization factor= cross sectional area + gross area of the core
b) utilization factor= cross sectional area – gross area of the core
c) utilization factor= cross sectional area * gross area of the core
d) utilization factor= cross sectional area / gross area of the core

View Answer

Answer: d [Reason:] The utilization factor is equal to the ratio of the cross sectional area to the gross area of the core. The cross sectional area and the gross area of the core are first found out, and the ratio gives utilization factor.

3. What is the relationship between utilization factor and the number of core steps?
a) utilization factor is directly proportional to the number of core steps
b) utilization factor is indirectly proportional to the number of core steps
c) utilization factor is indirectly proportional to the square of number of core steps
d) utilization factor is directly proportional to the square of number of core steps

View Answer

Answer: a [Reason:] The utilization factor increases with the increase in the number of core steps used. This eventually increases the manufacturing cost.

4. What is the optimum number of steps for small and large transformers?
a) 5,10
b) 10,15
c) 6,15
d) 1,10

View Answer

Answer: c [Reason:] The optimum number of steps used for the large transformers is maximum of 15. The optimum number of steps for the small transformers is maximum of 6.

5. What happens if the utilization factor gets improved?
a) core area increases and the volt/turns decreases
b) core area increases and the volt/turns increases
c) core area decreases and the volt/turn decreases
d) core area decreases and the volt/turn increases

View Answer

Answer: b [Reason:] When the utilization factor increases the core area gets increased. This leads to the increase in the volt/turn for any particular core diameter and specified flux density.

6. How many types of cores are available for core type of transformer?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] There are basically 3 types of core section available for core type of transformer. They are rectangular, square or stepped type of core sections.

7. What type of core section is used for shell type transformer?
a) rectangular
b) square
c) stepped
d) cruciform

View Answer

Answer: a [Reason:] Shell type transformers prefer only rectangular core section. Shell type transformer are moderate and low voltage transformer which use only rectangular core section.

8. What is the range of the ratio of depth to width of core in rectangular core?
a) 1-2
b) 1.5-2.5
c) 1.4-2
d) 1.5-2

View Answer

Answer: c [Reason:] In rectangular core, the ratio of the depth to core should be minimum 1.4. The maximum value of ratio of depth to core is 2.

9. When is square and stepped cores used?
a) when circular coils are required for low voltage distribution
b) when rectangular coils are required for low voltage distribution
c) when circular coils are required for high voltage distribution
d) when rectangular coils are required for high voltage distribution

View Answer

Answer: c [Reason:] Circular coils are required for high voltage distribution and power transformer. When circular coils are required square and stepped cores are used.

10. Circular coils are preferred because of their electrical characteristics?
a) true
b) false

View Answer

Answer: b [Reason:] Circular coils are preferred because of their high mechanical strength. Their high mechanical strength allows them to be used in high voltage distribution and power transformer.

11. What is the ratio of the net core area to the area of the circumscribing circle in square cores?
a) 0.58
b) 0.64
c) 0.70
d) 0.80

View Answer

Answer: a [Reason:] 0.64 is the ratio of the gross core area to the area of the circumscribing circle. Net core area is the product of stacking factor and gross iron area.

12. The laminations are manufactured in standard size to minimize the wastage of steel during punching of laminations?
a) true
b) false

View Answer

Answer: a [Reason:] The laminations are manufactured in the standard size of width, 0.75m to 1 m. This is used to avoid excessively wide assortment of laminations and to minimize wastage of steel during punching of laminations.

13. What is the value of ratio of gross core area to the area of circumscribing circle in stepped cores?
a) 0.71
b) 0.79
c) 0.89
d) 0.91

View Answer

Answer: b [Reason:] 0.71 is the ratio of net core area to the area of circumscribing circle in stepped cores. The gross core area for stepped cores is 0.618 * d2.

14. What is the net core area for three stepped transformers?
a) 0.45
b) 0.56
c) 0.6
d) 0.62

View Answer

Answer: c [Reason:] 0.45 is the net core area for the square core transformers. 0.56 is the core area for cruciform or stepped core transformers.

15. What is the relationship between the number of steps to the area of circumscribing circle?
a) number of steps is directly proportional to the area of the circumscribing circle
b) number of steps is indirectly proportional to the area of the circumscribing circle
c) number of steps is directly proportional to square of the area of the circumscribing circle
d) number of steps is indirectly proportional to square of the area of the circumscribing circle

View Answer

Answer: a [Reason:] As the number of steps increase, the area of the circumscribing circle also increases. But as the area of the circumscribing circle increases, the ratio of the net core area and gross core area to the area of circumscribing circle decreases.

Set 5

1. How many design factors are involved in the CAD design of DC motors?
a) 5
b) 6
c) 7
d) 4

View Answer

Answer: b [Reason:] There are 6 types of design factors involved in the CAD design of DC motors. They are main dimension, armature winding, design of field winding, design of commutator, design of interpoles, losses and efficiency.

2. What is the symbol used for the terminal voltage in dc motor design?
a) V
b) Vs
c) Vt
d) Tv

View Answer

Answer: c [Reason:] Computer aided design is one of the design algorithms made use of in the design of various machines. The symbol used for the terminal voltage is Vt.

3. What is the symbol used for the slot per pole arc in dc motor design?
a) sppa
b) spa
c) ssa
d) sp

View Answer

Answer: b [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for slot per pole arc in dc motor design is spa.

4. What is the symbol used for the flux density produced in the pole body of dc motor design?
a) fp
b) fdp
c) fyp
d) fypd

View Answer

Answer: c [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for flux density produced in the pole body of dc motor design is fyp.

5. What is the symbol used for the total mmf required for the teeth?
a) AT
b) ATt
c) Tm
d) Tmt

View Answer

Answer: b [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for total mmf required for the teeth is ATt.

6. What is the symbol used for the pitch of commutator segments in the dc motor?
a) Pc
b) Pcs
c) BETAc
d) Ret

View Answer

Answer: c [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for pitch of commutator segments is BETAc.

7. How many design steps are involved in the design of main dimensions of synchronous machine?
a) 10
b) 9
c) 7
d) 8

View Answer

Answer: a [Reason:] There are 10 steps in the flowchart of design of the main dimensions of synchronous machines. There are 8 design data in the design of the synchronous machine using CAD.

8. What is the number of design steps involved in the length of air gap?
a) 7
b) 8
c) 9
d) 10

View Answer

Answer: d [Reason:] There are 8 design data involved in the design of synchronous machine using CAD. There are 10 steps in the flowchart of the length of air gap in the CAD design of synchronous machine.

9. What is the number of design steps involved in the stator?
a) 6
b) 7
c) 8
d) 9

View Answer

Answer: b [Reason:] There are 8 design data involved in the design of synchronous machine using CAD. There are 7 steps in the flowchart of the stator design in the CAD design of synchronous machine.

10. What is the number of design steps involved in the number of slots?
a) 4
b) 5
c) 6
d) 7

View Answer

Answer: c [Reason:] There are 8 design data involved in the design of synchronous machine using CAD. There are 6 steps in the flowchart of the number of slots in the CAD design of synchronous machine.

11. What is the symbol used for the armature mmf per pole?
a) AT
b) ATM
c) Amp
d) ATa

View Answer

Answer: d [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for the armature mmf per pole is Ata.

12. What is the symbol used for the width of the ventilating duct?
a) Wv
b) Nw
c) Wvd
d) Wvds

View Answer

Answer: b [Reason:] Computer aided design in one of the design algorithms made use of to design various devices. The symbol used for width of the ventilating ducts is Nw.