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Multiple choice question for engineering

Set 1

1. What bearing is made use of in the horizontal shaft machines?
a) plain bearing
b) thrust bearing
c) push bearing
d) throw bearing

View Answer

Answer: a [Reason:] The plain bearing is made use of in the horizontal shaft machine. The thrust bearing are used for vertical shaft machine.

2.What is the plain bearing used?
a) sleeve bearings
b) anti friction bearing
c) sleeve or anti friction bearing
d) sleeve and anti friction bearing

View Answer

Answer: c [Reason:] The plain bearing can be the sleeve bearings made use of. It can also be friction bearings used which is either ball or roller bearings.

3. In horizontal shaft machines, the forces acting in which direction is prominent?
a) circular
b) vertical
c) horizontal
d) radial

View Answer

Answer: d [Reason:] Plain bearings are made use of for the horizontal shaft machines. The forces acting in the radial direction are most prominent.

4.In vertical shaft machines, which load is taken up by the thrust bearings?
a) perpendicular load acting upwards
b) perpendicular load acting downwards
c) axial load acting upwards
d) axial load acting downwards

View Answer

Answer: d [Reason:] The thrust bearings are made use of for the vertical shaft machines. In vertical shaft machines, the axial load acting downwards is taken up by the thrust bearings.

5. How are the radial loads caused?
a) dynamic unbalance of rotor
b) unbalanced magnetic pull of rotor
c) dynamic unbalance of rotor or unbalanced magnetic pull of rotor
d) dynamic unbalance of rotor and unbalanced magnetic pull of rotor

View Answer

Answer: c [Reason:] The radial loads are caused by the dynamic unbalance of rotor. It can also be caused by the unbalanced magnetic pull of rotor.

6. What is the additional setup provided to the simple thrust bearing when it is not able to take up radial loads?
a) ball bearing
b) gear bearing
c) steel bearing
d) guide bearing

View Answer

Answer: d [Reason:] Sometimes the simple thrust bearing wont be able to pull the radial loads. Therefore an additional bearing called guide bearing is provided.

7. How many guide bearings are used along with the simple thrust bearings to pick up radial loads?
a) 2
b) 3
c) 2 or 3
d) 4

View Answer

Answer: c [Reason:] The simple thrust bearing cannot pull the radial load and hence guide bearings are used in addition to it. Usually 2-3 guide bearings are used in vertical shaft machines depending upon the load.

8. Where are the bearings for the horizontal shaft placed ?
a) outside the machine
b) in the end shields of the machine
c) outside the machine or in the end shields of the machine
d) outside the machine and in the end shields of the machine

View Answer

Answer: c [Reason:] The bearings for the horizontal shaft machines are being placed outside the machine. It can also be placed along the end shields of the machine.

9. What is the other name of the bearings outside the machine?
a) ball bearing
b) pedestal bearing
c) guide bearing
d) gear bearing

View Answer

Answer: b [Reason:] The bearings for the horizontal shaft machines are placed outside the machine or in the end shields of the machine. The other name for the bearings outside the machine is pedestal bearing.

10. The phosphor bronze sleeve bearings are used for the small electrical machines ?
a) true
b) false

View Answer

Answer: a [Reason:] The phosphor bronze sleeve bearings are used for the small electrical machines. The diameter of the machines are between 50-60 mm.

11. Anti-friction bearings are lubricated by charcoal ?
a) true
b) false

View Answer

Answer: b [Reason:] Anti-friction bearings are one type of bearing used to take radial loads. They are always lubricated by grease.

Set 2

1. What is the other name for the iron loss?
a) field loss
b) armature loss
c) winding loss
d) core loss

View Answer

Answer: d [Reason:] When ferromagnetic materials are subjected to a flux in a fixed direction in space and having a magnitude varying in time, losses are produced in the machine. This is called as iron loss or core loss.

2. How many types of iron losses are present?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] There are basically 2 losses present under the core loss or iron loss. They are hysteresis loss and the eddy current loss.

3. What is the formula to obtain the hysteresis loss devised by Steinmetz?
a) hysteresis loss = hysteresis coefficient / frequency of magnetization * (maximum flux density)steinmetz coefficient
b) hysteresis loss = hysteresis coefficient * frequency of magnetization / (maximum flux density)steinmetz coefficient
c) hysteresis loss = hysteresis coefficient * frequency of magnetization * (maximum flux density)steinmetz coefficient
d) hysteresis loss = 1/hysteresis coefficient * frequency of magnetization * (maximum flux density)steinmetz coefficient

View Answer

Answer: c [Reason:] The hysteresis coefficient along with the frequency of magnetization and maximum flux density is calculated first. Next the Steinmetz coefficient is calculated and on substitution it gives the hysteresis loss.

4.How are the eddy current losses in the machine reduced?
a) by using conducting materials
b) by using magnetic materials
c) by using insulating materials
d) by laminating the core

View Answer

Answer: d [Reason:] Eddy current loss is one type of loss present under the iron or core loss. It can be reduced by laminating the core.

5. What is the relation between resistivity, magnetizing mmf and magnetizing current?
a) high resistivity, low magnetizing mmf, high magnetizing current
b) high resistivity, high magnetizing mmf, high magnetizing current
c) low resistivity, high magnetizing mmf, high magnetizing current
d) low resistivity, high magnetizing mmf, low magnetizing current

View Answer

Answer: b [Reason:] The high resistivity materials are made use of to reduce the eddy current loss. The high resistivity materials have high magnetizing mmf which in turn leads to high magnetizing current.

6. What must be done in order to take additional iron losses into account in dc machines?
a) iron loss obtained from iron loss curve is multiplied by 1.2-1.4
b) iron loss obtained from iron loss curve is multiplied by 1.4-1.6
c) iron loss obtained from iron loss curve is multiplied by 1.3-1.5
d) iron loss obtained from iron loss curve is multiplied by 1.15-1.25

View Answer

Answer: b [Reason:] In order to take additional losses into account the iron loss obtained from the iron loss curves is multiplied into 1.4-1.6 in dc machines and synchronous machines. The iron loss obtained from the iron loss curves is multiplied into 1.2-1.4 in induction motors.

7. What is the value of constant ‘a’ in the core part of the ac machines?
a) 4.7
b) 6.5
c) 6.7
d) 2.3

View Answer

Answer: a [Reason:] The value of constant ‘a’ in the core part of the ac machines is 4.7 and that in the teeth part is 6.5. The value of constant ‘a’ in the core part of the dc machines is 6.5 and that in the teeth part is 2.3.

8.What are the equations that are to be satisfied by flux patterns?
a) Poisson equation
b) Laplace equation
c) Laplace and Poisson equation
d) Gauss equation

View Answer

Answer: c [Reason:] The flux patterns must satisfy the Poisson equation within the section of the conductors. The flux patterns must satisfy the Laplace equation in the other parts.

9. How many assumptions can be used for the slot leakage calculation?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] There are 3 assumption made in the slot leakage calculation. They are the current in the slot conductors is uniformly distributed, the leakage path is straight across the slot and around the iron at the bottom and the permeance of air paths is only considered.

10. What are the factors the slot leakage permeance will depend upon?
a) shape of the slot
b) arrangement of winding in the slot
c) number of windings
d) shape of the slot and arrangement of winding in the slot

View Answer

Answer: d [Reason:] The slot leakage permeance depends upon the shape of the slots. The slot leakafe permeance also depends upon the arrangement of winding in the slot.

11.What is the formula of the permeance of the strip in the conductor portion?
a) permeance of the strip = permeability in air * area of the flux path * length of flux path
b) permeance of the strip = permeability in air / area of the flux path * length of flux path
c) permeance of the strip = permeability in air * area of the flux path / length of flux path
d) permeance of the strip =1 / permeability in air * area of the flux path * length of flux path

View Answer

Answer: c [Reason:] The permeability in air, area of the flux path and the length of flux path is first calculated. On substitution the permeance of the strip is obtained.

12. What is the formula of the effective permeance of conductor portion?
a) effective permeance of conductor portion = 1/total flux linkages * total turns * total mmf
b) effective permeance of conductor portion = total flux linkages / total turns * total mmf
c) effective permeance of conductor portion = total flux linkages * total turns * total mmf
d) effective permeance of conductor portion = total flux linkages * total turns / total mmf

View Answer

Answer: b [Reason:] The total flux linkages, total turns and total mmf is first calculated. On substitution the effective permeance of conductor portion is obtained.

13.Which machine incorporates the usage of the closed slots?
a) dc motors
b) synchronous motors
c) induction motors
d) special motors

View Answer

Answer: c [Reason:] The closed slots are being made use often in the small induction motors. The closed slots are used to increase the leakage reactance which in turn decreases the starting current.

14. The leakage flux on the top of the slot is through iron, which is called ‘bridge’?
a) true
b) false

View Answer

Answer: a [Reason:] The leakage flux on the top of the slot is through iron, which is called ‘bridge’. Therefore the specific permeance of this path depends upon the permeance of iron which in turn depends upon the degree of saturation and hence upon the relative permeability of iron.

Set 3

1. What type of core does the electromagnetic consist of?
a) paramagnetic
b) diamagnetic
c) ferromagnetic
d) paramagnetic and diamagnetic

View Answer

Answer: c [Reason:] Electromagnets consists of a ferromagnetic core. It carries the flux and a winding which produces a flux when excited by an external source.

2. What material is used for the construction of core of electromagnets?
a) soft magnetic materials
b) hard magnetic materials
c) non-magnetic materials
d) anti-ferromagnetic materials

View Answer

Answer: a [Reason:] The electromagnets consist of ferromagnetic core. The soft magnetic materials are made use of in the construction of core of electromagnets.

3. What are the ferromagnetic elements used in the electromagnets?
a) iron
b) nickel
c) cobalt
d) iron, nickel, cobalt

View Answer

Answer: d [Reason:] The electromagnets consist of ferromagnetic core. The ferromagnetic materials include iron. nickel and cobalt.

4. What are the non-magnetic materials being used in the electromagnets?
a) silicon
b) molybdenum
c) silicon, chromium, molybdenum
d) chromium

View Answer

Answer: c [Reason:] The electromagnets consists of the ferromagnetic core. Some times the non-ferro-magnetic materials are being made use of like silicon, chromium and molybdenum.

5. Coils are being made use of in electromagnets as an exciting source for production of magnetic field?
a) true
b) false

View Answer

Answer: a [Reason:] The coils are being made use of in electromagnets. They are used as an exciting source for the production of magnetic field.

6. What is the insulation material being used in the electromagnets?
a) paper
b) wood
c) brass
d) copper

View Answer

Answer: a [Reason:] Insulation material is being used in between the coils of the electromagnet to provide insulation. The material used in the electromagnet is paper.

7. What is the conductor material being used in the electromagnet?
a) copper
b) zinc
c) bronze
d) aluminum

View Answer

Answer: a [Reason:] Conductor materials are being used in the electromagnet to conduct the current in the electromagnet. Copper is the material used in the electromagnet.

8. What type of conductors are being used in the coils made of heavy wire?
a) circular
b) rounded
c) conical
d) rectangular

View Answer

Answer: d [Reason:] The cross-section of coils is generally rectangular and the cross-section of conductors is usually rounded. The coils made of heavy wires, rectangular conductors with rounded corners are used.

9. The coil insulation used in the electromagnets is of sheet form?
a) true
b) false

View Answer

Answer: a [Reason:] Insulation material used in the machine is usually paper. The insulation is arranged in the form of sheets.

10. What materials are used along with paper for insulation?
a) varnish
b) glass
c) synthetic resin
d) varnish, glass, synthetic resin

View Answer

Answer: d [Reason:] The insulation used in the electromagnets is paper. It is being insulated along with the varnish, glass and synthetic resin and treated into form of sheets to form proper insulation.

Set 4

1. How many factors are involved in the construction of hydro-generators?
a) 11
b) 10
c) 9
d) 8

View Answer

Answer: b [Reason:] The hydro-generators are the synchronous generators which are driven by the water turbines. They are chosen based on 10 different categories.

2. Which factor does the constructional feature of the hydro-generators depend on?
a) speed
b) voltage
c) power
d) current

View Answer

Answer: a [Reason:] The constructional feature of hydro-generators are basically dependent upon the mechanical considerations. The main mechanical consideration is speed of the machine.

3. What factors does the speed of the machines depend upon?
a) head
b) blades
c) type of turbine used
d) head and type of turbine used

View Answer

Answer: d [Reason:] The hydro-generators are generally low speed machines. The speed depends upon the head and the type of turbines used.

4. Why is the stator core built up of laminations?
a) to reduce core loss
b) to reduce copper loss
c) to reduce iron loss
d) to reduce eddy current loss

View Answer

Answer: d [Reason:] The stator core is built up of laminations in order to reduce the eddy current loss. The loss in the laminated core is usually the single largest loss and hence the choice of type and grade of steel is of utmost importance.

5. The modern synchronous machines make use of non-directional cold rolled steel?
a) true
b) false

View Answer

Answer: a [Reason:] The modern synchronous machines make use of the non-directional cold rolled steel which has electrical characteristics similar to that of the hot rolled steel. But the non-directional cold rolled steel has a much improved mechanical characteristics.

6. What is the thickness of the most commonly used grade for stator laminations?
a) 0.5 mm
b) 1 mm
c) 1.5 mm
d) 2 mm

View Answer

Answer: a [Reason:] The most commonly used grade for the stator laminations is grade 230. The thickness of this most commonly used grade for the stator laminations is 0.5 mm.

7. What is the range of the outside diameter of the stator frame of the large hydro-generator?
a) 3-18 m
b) 2-18 m
c) 3.5-18 m
d) 4-18 m

View Answer

Answer: c [Reason:] The minimum value for the outside diameter of the stator frame of the large hydro-generators is 3.5 m. The maximum value for the outside diameter of the stator frame of the large hydro-generators is 18 m.

8. How are the stator windings of all synchronous generator connected ?
a) star-delta connection
b) star connection
c) star connection with neutral earthed
d) delta connected

View Answer

Answer: c [Reason:] The stator windings of all the synchronous generator are connected in the star connection with neutral earthing. The main advantage that the winding has to be insulated to earth for the phase voltage and not the line voltage.

9. What among the following is the advantages of the star connection?
a) eliminates single frequency harmonics
b) eliminates double frequency harmonics
c) eliminates triple frequency harmonics
d) eliminates sinusoidal harmonics

View Answer

Answer: c [Reason:] The hydro-generators stator windings are connected in the star connected with the neutral earthed. It eliminates the triple frequency harmonics from the line voltage.

10. The capacity of the pull out machines used for making the coils limits the pole pitch to less than 0.8 m?
a) true
b) false

View Answer

Answer: a [Reason:] The capacity of the pull out machines used for making the coils limits the pole pitch to less than 0.8 m. The capacity of the pull out machines used for making coils limits the length of slot portion to about 3 m.

11. What is the main advantage of a winding with multi-turns coils?
a) reduce the choosing of the value of stator slots
b) allows greater flexibility in selecting the value of stator slots
c) increases the flexibility in selecting the number of stator slots
d) has no effect on the number of stator slots

View Answer

Answer: b [Reason:] The main advantage of a winding with multi-turns coils is that it allows a greater flexibility in selecting the value of stator slots. It in turn helps in choosing the required number of turns per phase.

12. What happens to the current in the windings during the sudden short circuits at the line terminals?
a) the current reduces to 15 times the full load current
b) the current increases to 15 times the full load current
c) the current reduces to 10 times the full load current
d) the current increases to 10 times the full load current

View Answer

Answer: b [Reason:] The current in the windings during short circuit at the line terminals increases to about 15 times the full load current. It can also increase to higher level depending on the direct axis sub-transient reactance.

13. What happens to the electromagnetic forces during the sudden short circuits at the line terminals?
a) the electromagnetic forces get increased by 250 times the force under normal full load condition
b) the electromagnetic forces get decreased by 250 times the force under normal full load condition
c) the electromagnetic forces get increased by 200 times the force under normal full load condition
d) the electromagnetic forces get decreased by 200 times the force under normal full load condition

View Answer

Answer: a [Reason:] The electromagnetic forces are directly proportional to the square of the current. It increases by 250 times the force under normal full load condition.

14. What should be done to the conductors in the overhang of the stator?
a) bracing
b) shaving
c) punching
d) compressing

View Answer

Answer: a [Reason:] The conductors in the overhang of the stator must be braced. Bracing is the process of raising the mechanical strength of the conductors.

15. How many steel brackets are used along with the support to steel rings?
a) 5
b) 7
c) 4-6
d) 5-9

View Answer

Answer: c [Reason:] During the process of bracing one or two circular steel rings are used to support the overhang. Along with the steel rings 4-6 steel brackets are also used.

Set 5

1. How many factors does the construction of the turbo alternators depend upon?
a) 2
b) 4
c) 3
d) 6

View Answer

Answer: c [Reason:] There are 3 factors which decide the construction of the turbo-alternators. They are i) stator core ii) stator winding iii) rotor.

2.How many poles does the turbo-alternators have and what is the speed of the turbo alternators?
a) 4 poles, 3000 rpm
b) 3 poles, 6000 rpm
c) 2 poles, 5000 rpm
d) 2 poles, 3000 rpm

View Answer

Answer: d [Reason:] The turbo-alternators are made up of 2 poles. The speed with which the turbo alternators operate are 3000 rpm.

3. What is the relation of the lengths and diameters with the turbo-alternators?
a) long length, long diameters
b) long length, short diameters
c) short lengths, short diameters
d) short lengths, long diameters

View Answer

Answer: b [Reason:] The turbo-alternators are characterized by the long lengths. The turbo-alternators are also characterized by short diameters.

4.What is the core length and the shaft length of a 500 MW turbo alternator?
a) 5 m , 12 m
b) 6 m, 15 m
c) 3 m, 10 m
d) 4 m, 13 m

View Answer

Answer: a [Reason:] The core length of a 500 MW turbo alternator is 5 m. The shaft length of the 500 MW turbo alternator is 12 m.

5. What is the outer diameter of the stator core and outer casing of 500 MW turbo alternator?
a) 5 m , 2 m
b) 6 m, 5 m
c) 3 m, 4 m
d) 4 m, 7 m

View Answer

Answer: c [Reason:] For a 500 MW turbo alternator the outer diameter of the stator core is 3 m. The diameter of the outer casing is 4 m.

6. What type of lamination is used for the stator core of the turbo alternators?
a) stepped
b) smooth
c) interleaved
d) segmental

View Answer

Answer: d [Reason:] The stator core is made up of segmental laminations. The grain oriented steel laminations are another type of stator laminations made use of.

7. What is the advantage of the grain oriented steel laminations?
a) it lowers the iron loss
b) it lowers the core loss
c) it lowers the heating effects
d) it lowers the harmonics

View Answer

Answer: b [Reason:] The grain oriented steel laminations are also one type of laminations used for the stator core. They result in the lowering of the core loss.

8. What is the pulsational force produced for 500 MW machine?
a) 70 kN per m
b) 60 kN per m
c) 80 kN per m
d) 90 kN per m

View Answer

Answer: c [Reason:] The generator designed with low voltage gives high currents which produce high pulsational forces. The pulsational forces can be as high as 80 kN per m.

9. What is the use of the laminated and transposed conductors in turbo alternators?
a) to decrease the harmonics
b) to decrease the heating effects
c) to decrease the iron and core loss
d) to decrease the eddy current loss

View Answer

Answer: d [Reason:] The presence of large currents requires the use of multi circuit windings. The use of the laminated and transposed conductors in turbo alternators is to reduce the eddy current loss.

10. What is the voltage range for large turbo-alternators?
a) 15-20 kV
b) 18-23 kV
c) 20-23 kV
d) 20-25 kV

View Answer

Answer: d [Reason:] The generation voltage normally used are 15 kV for 100-200 MW machines. The voltage range for the large turbo-alternators are 20-25 kV.

11. The overhang has to be highly reinforced in turbo alternators?
a) true
b) false

View Answer

Answer: a [Reason:] The overhang has to be highly reinforced in turbo alternators. The overhang is distributed over a large number of sections which eliminates the concentration of conductors in the overhang.

12. What is the use of the slot in the rotor?
a) for inserting the field windings
b) for inserting the armature windings
c) for securing the field windings
d) for inserting and securing the field windings

View Answer

Answer: d [Reason:] The rotors slots are used for inserting the field windings. The rotor slots are also used for securing the field windings also.

13. How many types are the rotor slots distinguished into?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: a [Reason:] There are 2 types of rotor slots in the turbo-alternators. They are i) radial sort ii) parallel slot rotors.

14. The rotor is slotted for one-third of its periphery?
a) true
b) false

View Answer

Answer: b [Reason:] The rotor is slotted for only two-thirds of its periphery. It is because to reduce the flux pulsations and the cost factors.

15. What is the mechanical strength of the end bells used?
a) 1120 MN per m2
b) 1130 MN per m2
c) 1150 MN per m2
d) 1140 MN per m2

View Answer

Answer: c [Reason:] The end bells are made of a non-magnetic austenitic steel in order to reduce the leakage flux. The end bells have high mechanical strength of about 1150 MN per m2.

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