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Multiple choice question for engineering

Set 1

1. What are the applications of the small universal commutator motors?
a) industry
b) medicine
c) domestic sector
d) industry, medicine and domestic sector

View Answer

Answer: d [Reason:] Small universal commutator motors have power outputs varying from few watts to hundreds of watts. They have lots of application in industry, medicine, domestic sector.

2. What type of excitation is used in the small universal commutator motors and what type of supply is provided?
a) parallel excitation, dc supply
b) series excitation, dc or ac supply
c) series excitation, ac supply
d) parallel excitation, dc supply

View Answer

Answer: b [Reason:] The excitation which is provided is the series excitation in the small universal commutator motors. The type of supply provided is dc or ac supply.

3. What is the material used in the lamination of the magnetic poles of small universal commutator motor?
a) copper
b) aluminium
c) gold
d) sheet steel

View Answer

Answer: d [Reason:] Unlike dc motors universal commutator motors are having laminated poles. The laminated poles are laminated using the sheet steel.

4.What is the thickness of the laminations of magnetic poles?
a) 0.3-0.5 mm
b) 0.2-0.4 mm
c) 0.35-0.5 mm
d) 0.4-0.5 mm

View Answer

Answer: c [Reason:] The minimum value of the thickness of the laminations of magnetic poles is 0.35 mm. The maximum value of the thickness of the laminations of magnetic poles is 0.5 mm.

5. How many type of excitations does the universal commutator motors have?
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: b [Reason:] There are two kinds of excitation present for the universal commutator motors. One winding is intended to run the motor to ac supply voltage. The other winding is connected in series with the first winding when the motor is operated from dc supply voltage.

6. The number of turns of field winding in the motor must be considerably less than the number of turns in the armature winding?
a) true
b) false

View Answer

Answer: a [Reason:] The number of turns of field winding in the motor must be considerably less than the number of turns in the armature winding. The speed of the machine is irrespective of the supply.

7. What is the relation of the copper loss and brush contacts with the total loss in small dc motors?
a) copper loss and brush contacts = 2 * total loss
b) copper loss and brush contacts = 2/3 * total loss
c) copper loss and brush contacts = 1/3 * total loss
d) copper loss and brush contacts = total loss

View Answer

Answer: b [Reason:] The copper loss and brush contact loss is being compared with the total loss in order to deduce an equation. The copper loss and brush contact loss is 2/3 times the total loss.

8. What is the relation of the copper loss and brush contacts with the total loss in universal commutator motors?
a) copper loss and brush contacts = total loss
b) copper loss and brush contacts = total loss/2
c) copper loss and brush contacts = total loss * 2
d) copper loss and brush contacts = total loss *3

View Answer

Answer: b [Reason:] The copper loss and brush contact loss is being compared with the total loss in order to deduce equations. The copper loss and brush contact loss is half the total loss.

9. What is the range of the transformation ratio in the pole machines?
a) 0.05-0.1
b) 0.1-0.2
c) 0.1-0.25
d) 0.3-0.4

View Answer

Answer: c [Reason:] The transformation ratio in 2 pole motors is 0.1-0.25. The transformation ratio in the 4 pole motors is 0.05-0.1.

10. For what outputs are the 2 pole machines made use of?
a) output > 200 W
b) output < 200 W
c) output > 300 W
d) output < 300 W

View Answer

Answer: b [Reason:] The 2 pole machines are made use of when the output is below 200 W. The 4 pole machines are made use of when the output is above 200 W.

11. What is the range of the power factor for the 4 pole motors?
a) 0.6-0.85
b) 0.75-0.95
c) 0.6-0.8
d) 0.7-0.9

View Answer

Answer: a [Reason:] The power factor for the 4 pole motors is 0.6-0.85. The power factor for the 2 pole motors is 0.75-0.95.

12. What is the value of the specific electric loading for the continuous duty motor type?
a) 8000-11000 A per m
b) 6000-9000 A per m
c) 12000-20000 A per m
d) 15000-25000 A per m

View Answer

Answer: b [Reason:] The specific electric loading for continuous duty motor type is 6000-9000 A per m. The specific electric loading for power rating above 100 W but below 200 W is 8000-11000 A per m and the specific electric loading for power rating above 200 W but below 750 W is 12000-20000 A per m.

13. What is the specific magnetic loading for the motors having output less than 100 W?
a) 0.25-0.30 T
b) 0.3-0.4 T
c) 1.3-1.5 T
d) 0.25-0.35 T

View Answer

Answer: d [Reason:] The specific magnetic loading for the output below 100 W is 0.25-0.35 T and the specific magnetic loading for the continuous duty motors is 0.3-0.4 T and the specific magnetic loading for the short time duty motors is 1.3-1.5 T.

14. What is the formula for the pole pitch in the universal commutator motor?
a) pole pitch = 3.14 * diameter * 2 * no. of poles
b) pole pitch = 3.14 / diameter * 2 * no. of poles
c) pole pitch = 3.14 * diameter / 2 * no. of poles
d) pole pitch = 3.14 * diameter * 2 / no. of poles

View Answer

Answer: c [Reason:] The diameter and the number of poles are calculated. On substitution the pole pitch of the universal commutator motor is obtained.

15. What is the formula of the pole arc of the universal commutator motor?
a) pole arc = ratio of armature axial length to armature diameter * pole pitch
b) pole arc = ratio of armature axial length to armature diameter + pole pitch
c) pole arc = ratio of armature axial length to armature diameter – pole pitch
d) pole arc = ratio of armature axial length to armature diameter / pole pitch

View Answer

Answer: b [Reason:] Firstly the ratio of armature axial length to armature diameter is calculated. Next the pole pitch is calculated and on addition of both the terms the pole arc is obtained.

Set 2

1. What is the formula for the depth and height of the yoke for stepped core?
a) depth = width of largest stamping, height = 2* width of largest stamping
b) depth = 2*width of largest stamping, height = width of largest stamping
c) depth = width of largest stamping, height = width of largest stamping
d) depth = 2*width of largest stamping, height = 2* width of largest stamping

View Answer

Answer: c [Reason:] The depth of the yoke of stepped core is equal to the width of the largest stamping. The height of the yoke for the stepped core is also equal to the width of the largest stamping.

2.The height and the width of the single phase and three phase core type transformer equal?
a) true
b) false

View Answer

Answer: b [Reason:] The height of both the single phase and three phase core type transformers are equal. The width of the single phase and three phase core type are not same.

3. What is the formula for height and width of the single phase shell transformer?
a) width = 2*width of the window + 4*width of the largest stamping, height = height of the window + 2*width of the largest stamping
b) width = 2*width of the window – 4*width of the largest stamping, height = height of the window + 2*width of the largest stamping
c) width = 2*width of the window + 4*width of the largest stamping, height = height of the window – 2*width of the largest stamping
d) width = 2*width of the window – 4*width of the largest stamping, height = height of the window -2*width of the largest stamping

View Answer

Answer: a [Reason:] First the width of the window is obtained. Next the height of the window is obtained. Then, the width of the largest stamping is obtained and substituted in the above formula.

4.What is the formula to calculate the number of turns/phase?
a) number of turns = secondary voltage * voltage per turn
b) number of turns = secondary voltage / voltage per turn
c) number of turns = secondary voltage + voltage per turn
d) number of turns = secondary voltage – voltage per turn

View Answer

Answer: b [Reason:] First the voltage across the secondary winding of the transformer is obtained. Next, the voltage across each turn is obtained. On substituting we get the number of turns.

5. What is the formula for the cross sectional area of the secondary conductor of the transformer?
a) cross sectional area = secondary current * current density
b) cross sectional area = secondary current + current density
c) cross sectional area = secondary current / current density
d) cross sectional area = secondary current – current density

View Answer

Answer: c [Reason:] The current flowing through the secondary winding of the transformer is calculated. Next the current density is calculated and the ratio gives the cross sectional area of the secondary conductor.

6. What is the formula for the conductor dimensions in transformer?
a) conductor dimensions = conductor width * conductor thickness + 0.5 mm
b) conductor dimensions = conductor width / conductor thickness + 0.5 mm
c) conductor dimensions = conductor width + conductor thickness + 0.5 mm
d conductor dimensions = conductor width – conductor thickness + 0.5 mm

View Answer

Answer: a [Reason:] The width of the conductor is first calculated. Next the thickness of the conductor is calculated. On obtaining these data the conductor dimensions can be obtained.

7. What is the formula for axial depth of low voltage winding?
a) axial depth = number of secondary turns / width of the conductor
b) axial depth = number of secondary turns * width of the conductor
c) axial depth = number of secondary turns + width of the conductor
d) axial depth = number of secondary turns – width of the conductor

View Answer

Answer: b [Reason:] The number of secondary turns is calculated first. Then the width of the conductor is obtained. With the 2 data, the axial depth is obtained.

8. What is the formula for window clearance of the transformer?
a) window clearance = (height of the window + axial depth)/2
b) window clearance = (height of the window – axial depth)
c) window clearance = (height of the window – axial depth)/2
d) window clearance = (height of the window + axial depth)

View Answer

Answer: c [Reason:] First the height of the window is obtained. Then the axial depth is calculated using the formula axial depth = number of secondary turns * width of the conductor and substituting in the above formula provides the window clearance.

9. What is the formula to calculate the radial depth of low voltage windings?
a) radial depth of the lv windings = number of layers * radial depth of the conductors * insulation between layers
b) radial depth of the lv windings = number of layers * radial depth of the conductors – insulation between layers
c) radial depth of the lv windings = number of layers / radial depth of the conductors + insulation between layers
d) radial depth of the lv windings = number of layers * radial depth of the conductors + insulation between layers

View Answer

Answer: d [Reason:] The number of layers is first taken note of. Then the radial depth of the conductors is calculated along with the insulation between layers. On substituting the values in the above formula the radial depth of the low voltage windings is obtained.

10. What is the formula for the inside diameter of the low voltage windings?
a) inside diameter = diameter of the circumscribing circle + pressboard thickness insulation between l.v winding and core
b) inside diameter = diameter of the circumscribing circle – pressboard thickness insulation between l.v winding and core
c) inside diameter = diameter of the circumscribing circle + 2*pressboard thickness insulation between l.v winding and core
d) inside diameter = diameter of the circumscribing circle – 2* pressboard thickness insulation between l.v winding and core

View Answer

Answer: c [Reason:] For calculating the inner diameter, first the diameter of the circumscribing circle is obtained using the corresponding formula. Then the pressboard thickness insulation is calculated.

11. What is the assumption for width of the largest stamping for the stepped core transformer?
a) 0.9*d
b) 0.71*d
c) 0.85*d
d) 0.8*d

View Answer

Answer: a [Reason:] If the width of the largest stamping is not provided, then for stepped core a = 0.9*d. For the cruciform it is a = 0.85*d and for the square core it is a = 0.71*d.

12. What is the range for the current density at HT side for a distribution transformer?
a) 2.4-3.5 Amp per mm2
b) 2-2.5 Amp per mm2
c) 1-3.5 Amp per mm2
d) 2-3.5 Amp per mm2

View Answer

Answer: b [Reason:] 2.4-3.5 Amp per mm2 is the range for the current density at HT side for a power transformer. 2-2.5 Amp per mm2 is the range for the current density at HT side for a distribution transformer.

13. What is the relation of the height of the window with the winding height with respect to the rectangular conductors?
a) winding height = 60% * window height
b) winding height = 50% * window height
c) winding height = 80% * window height
d) winding height = 70% * window height

View Answer

Answer: d [Reason:] In case of selection of the rectangular conductors, first the window height is obtained. Next the 70% of the window height provides the winding height.

14. What is the formula for number of turns/coil axially?
a) number of turns/coil axially = axial length / diameter of the insulated conductor
b) number of turns/coil axially = axial length * diameter of the insulated conductor
c) number of turns/coil axially = axial length – diameter of the insulated conductor
d) number of turns/coil axially = axial length + diameter of the insulated conductor

View Answer

Answer: a [Reason:] First the axial length is calculated from its respective formula. Then the diameter of the insulated conductor is calculated, and the ratio gives the number of turns/coil axially.

15. The axial length of 16 coils = axial length of each coil * 16?
a) true
b) false

View Answer

Answer: a [Reason:] The axial length of each coil is calculated initially from its corresponding formula. Then the value is multiplied by the number of coils present.

Set 3

1. What is specific permeance?
a) specific permeance is product of permeance of unit length and depth of field
b) specific permeance is ratio of permeance of unit length and depth of field
c) specific permeance is the permeance per unit length
d) specific permeance is the permeance per unit pole

View Answer

Answer: c [Reason:] Specific permeance is defined as permeance per unit length. It is also known as the depth of field.

2. What is the formula of the specific permeance?
a) specific permeance = permeability in air * ∫small change in width + length
b) specific permeance = permeability in air * ∫small change in width/length
c) specific permeance = permeability in air * ∫small change in width * length
d) specific permeance = 1/permeability in air * ∫small change in width * length

View Answer

Answer: b [Reason:] The permeability in air, small change in width and length is calculated first. On substitution the specific permeance is calculated.

3. What is the assumption made in the calculation of the specific permeance?
a) voltage is kept constant
b) current is kept constant
c) mmf is kept constant
d) speed is kept constant

View Answer

Answer: c [Reason:] The mmf is kept constant over all the flux tubes. The mmf should be kept constant when the integration is carried out during the calculation of specific permeance.

4.What is the formula of the effective permeance?
a) effective permeance = effective flux/total mmf
b) effective permeance = effective flux/mmf of air gap
c) effective permeance = effective flux * total mmf
d) effective permeance = effective flux * mmf of air gap

View Answer

Answer: a [Reason:] The effective flux and the total mmf is first calculated. On substitution of the values the effective permeance is calculated.

5. What is the formula of the flux dividing into infinitesimal parts?
a) flux dividing into infinitesimal parts = mmf producing the flux / permeance of infinitesimal part
b) flux dividing into infinitesimal parts = mmf producing the flux * permeance of infinitesimal part
c) flux dividing into infinitesimal parts = mmf producing the flux + permeance of infinitesimal part
d) flux dividing into infinitesimal parts = mmf producing the flux – permeance of infinitesimal part

View Answer

Answer: b [Reason:] The mmf producing the flux and the permeance of infinitesimal part is calculated. On substitution the flux dividing into infinitesimal parts is calculated.

6.What is the relation between the specific permeance of a differential path and the length?
a) specific permeance of a differential path is directly proportional to the length
b) specific permeance of a differential path is indirectly proportional to the length
c) specific permeance of a differential path is directly proportional to the square of the length
d) specific permeance of a differential path is indirectly proportional to the square of the length

View Answer

Answer: b [Reason:] The specific permeance is defined as the permeance per unit length. It is indirectly proportional to the length.

7.How many factors does the value of the magnetizing current depends upon?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] There are 3 factors upon which the magnetizing current depends upon. They are total mmf required, number of turns in the exciting winding and upon the way in which the winding is distributed.

8. What is the formula for the magnetizing current?
a) magnetizing current = total mmf * number of turns
b) magnetizing current = total mmf / number of turns
c) magnetizing current = total mmf + number of turns
d) magnetizing current = total mmf – number of turns

View Answer

Answer: b [Reason:] First the total mmf is calculated along with the number of turns of the magnetizing winding. Then on substitution the magnetizing current is obtained.

9. What is the formula for the rms value of the magnetizing current?
a) rms value of the magnetizing current = maximum magnetizing current / peak factor
b) rms value of the magnetizing current = maximum magnetizing current * peak factor
c) rms value of the magnetizing current = maximum magnetizing current + peak factor
d) rms value of the magnetizing current = maximum magnetizing current – peak factor

View Answer

Answer: a [Reason:] The maximum value of the magnetizing current and the peak factor are calculated first. On substitution the rms value of the magnetizing current is obtained.

10. What is the relation of the type of winding with the flux linkage?
a) in distributed windings the flux does not link with all the turns
b) in distributed windings the flux links with all the turns
c) in concentrated windings the flux links with all the turns
d) in concentrated windings the flux does not link with all the turns

View Answer

Answer: a [Reason:] The magnetizing current is actually calculated for the concentrated windings and the distributed windings. In the distributed windings, the flux does not link with all the turns.

11. What is the relation of the magnetizing current with the turns per phase?
a) magnetizing current is directly proportional to the turns per phase
b) magnetizing current is directly proportional to the square of the turns per phase
c) magnetizing current is indirectly proportional to the turns per phase
d) magnetizing current is indirectly proportional to the turns per phase

View Answer

Answer: c [Reason:] The magnetizing current is actually calculated for the concentrated windings and the distributed windings. In the distributed windings, magnetizing current is indirectly proportional to the turns per phase.

12. The plot of the flux density distribution curve is between the interpolar axis consisting of the flux density and the angle difference between phases?
a) true
b) false

View Answer

Answer: a [Reason:] The flux density distribution curve is used to calculate the magnetizing current in the non sinusoidal flux distribution of the distributed windings. The curve is between the flux density and the phase angle.

Set 4

1. What is the use of the wire bands of rotor?
a) used for bracing the rotor windings
b) used for circulating the current in the rotor windings
c) used for the encircling of the rotor windings
d) used for the protecting the rotor windings

View Answer

Answer: a [Reason:] Bands used on the rotors of electrical machines are intended for bracing the rotor windings. This is done against their shift in the radial direction under action of centrifugal forces.

2. Where are the wire bands placed?
a) active portions of rotor conductors
b) inactive portions of rotor conductors
c) active or inactive portions of rotor conductors
d) active and inactive portions of the rotor conductors

View Answer

Answer: d [Reason:] The wire bands are placed on the active portions of the rotor conductors. They are also placed in the inactive portions of the rotor conductors.

3. What are the factors on which the sizes of bands placed on depend?
a) length of air gap
b) method of cooling of armatures
c) length of air gap and method of cooling of armatures
d) method of cooling of armatures or length of air gap

View Answer

Answer: c [Reason:] The sizes of bands placed on the active portions of the conductors depends upon the length of air gap. They also depend upon the method of cooling of armatures.

4.In what machines are the wire bands along the active length of windings placed?
a) dc or ac machines
b) dc and ac machines
c) dc machines
d) ac machines

View Answer

Answer: c [Reason:] Wire bands are generally placed on both the active and inactive portions of rotor conductors. The wire bands along the active length of windings are placed along the dc machines.

5. What is the range of the width of the each band that should not be exceeded?
a) 10-15 mm
b) 15-20 mm
c) 20-25 mm
d) 18-23 mm

View Answer

Answer: b [Reason:] Bands placed along the active length of windings are housed in the ring slots. The width of each band should not exceed 15 to 20 mm.

6. What is the maximum value above which the total width of the bands should not exceed?
a) 25-35% of the axial length of armature core
b) 30-35% of the axial length of armature core
c) 25-30% of the axial length of armature core
d) 35-40% of the axial length of armature core

View Answer

Answer: a [Reason:] The total width should not exceed 25% of the axial length of the armature core. The total width should not exceed maximum of 35% of the axial length of the armature core.

7. What is the formula for the breadth of the ring slot?
a) breadth of the ring slot = (number of turns in a band + 1)*diameter of band wire – 2*constant
b) breadth of the ring slot = (number of turns in a band + 1)*diameter of band wire + 2*constant
c) breadth of the ring slot = (number of turns in a band + 1)*diameter of band wire * 2*constant
d) breadth of the ring slot = (number of turns in a band + 1)*diameter of band wire / 2*constant

View Answer

Answer: b [Reason:] The number of turns in a band is first calculated along with the diameter of band wire. The value of constant is just fixed and on substitution gives the breadth of the ring slot.

8. What is the value of the constant used in the calculation of the breadth of the ring slot for the diameter of band wire < 1.5 mm?
a) 1 mm
b) 1.5 mm
c) 2 mm
d) 3 mm

View Answer

Answer: a [Reason:] The value of the constant used in the calculation of the breadth of the ring slot is 1 mm for the diameter of band wire < 1.5 mm. The value of the constant used in the calculation of the breadth of the ring slot is 1.5 mm for the diameter of band wire > 1.5 mm.

9. What is the maximum width of the bands placed on the end windings of induction machines and high speed dc machines?
a) 30 mm
b) 35 mm
c) 40 mm
d) 45 mm

View Answer

Answer: c [Reason:] The maximum width are obtained for the bands placed on the end windings of induction machines and high speed dc machines. The maximum width is 40 mm.

10. What is the diameter of the wire bands made of tin, steel or bronze wire?
a) 2 mm
b) 1 mm
c) 4 mm
d) 3 mm

View Answer

Answer: d [Reason:] The wire bands are generally made up of tin, steel or bronze wires. The diameter of those wire bands are 3 mm.

11. What is the function of the bands when it is placed on overhang?
a) used to reduce the centrifugal forces
b) used to increase the centrifugal forces
c) used to balance the centrifugal forces
d) used to withstand the centrifugal forces

View Answer

Answer: d [Reason:] The bands when placed on overhead only are used to withstand the centrifugal forces. The centrifugal forces are due to the weight of the overhang.

12. What is the function of the bands when they are distributed along the axial length of armature?
a) used to reduce the centrifugal forces
b) used to increase the centrifugal forces
c) used to decrease the centrifugal forces
d) used to withstand the centrifugal forces

View Answer

Answer: d [Reason:] The bands are distributed along the axial length of the armature and they withstand the centrifugal forces. The centrifugal forces are due to the weight of both the active and inactive parts of armature.

13. What is the formula of the mean diameter at the position of centre of gravity?
a) mean diameter at the position of centre of gravity = Inner diameter + diameter of stator wires
b) mean diameter at the position of centre of gravity = Inner diameter * diameter of stator wires
c) mean diameter at the position of centre of gravity = Inner diameter / diameter of stator wires
d) mean diameter at the position of centre of gravity = Inner diameter – diameter of stator wires

View Answer

Answer: d [Reason:] The inner diameter and the diameter of the stator wires is first calculated. Then on substitution gives the mean diameter at the position of centre of gravity.

14. What is the value of permissible stress for bronze wire for the diameter of branding wire of 1 mm?
a) 350 NM per m2
b) 250 NM per m2
c) 300 NM per m2
d) 450 NM per m2

View Answer

Answer: a [Reason:] The permissible stress for bronze wire for the diameter of branding wire of 1 mm is 350 NM per m2. The permissible stress for bronze wire for the diameter of branding wire of 1.5 mm is 300 NM per m2.

15. What is the value of permissible stress for steel wire for the diameter of branding wire of 0.5-1.2 mm?
a) 570 NM per m2
b) 600 NM per m2
c) 650 NM per m2
d) 700 NM per m2

View Answer

Answer: b [Reason:] The value of permissible stress for steel wire for the diameter of branding wire of 0.5-1.2 mm is 600 NM per m2. The value of permissible stress for steel wire for the diameter of branding wire of 1.5-2 mm is 570 NM per m2.

Set 5

1. How many factors does the design of armature of synchronous machines depend upon?
a) 2
b) 4
c) 3
d) 5

View Answer

Answer: d [Reason:] There are 5 factors which decide the design of the armature of synchronous machines. They are i) single or double layer winding, ii) number of armature slots, iii) coil span, iv) turns per phase, v) conductor section.

2. When are the double layer bar windings made use of during the armature design?
a) large values of flux per pole and small number of turns per phase
b) large values of flux per pole and large number of turns per phase
c) small values of flux per pole and small number of turns per phase
d) small values of flux per pole and large number of turns per phase

View Answer

Answer: a [Reason:] The double layer bar windings are made use of when there is large values of flux per poles. The double layer bar windings are made use of when there are small number of turns per phase.

3. Which type of machines have a large number of poles per phase?
a) high voltage machines and machines with high value of flux per pole
b) high voltage machines and machines with small value of flux per pole
c) small voltage machines and machines with high value of flux per pole
d) small voltage machines and machines with low value of flux per pole

View Answer

Answer: b [Reason:] The high voltage machines have a large number of poles per phase. The small value of flux per pole per phase also results in large number of poles per phase.

4. Which among the following makes double layer windings advantageous than the single layer windings?
a) ease in the manufacture of coils and lower cost of winding
b) less number of coils are required as spare in the case of winding repairs
c) fractional slot windings can be employed
d) ease in the manufacture of coils and lower cost of winding, fractional slot windings can be employed, less number of coils are required as spare in the case of winding repairs

View Answer

Answer: d [Reason:] The double layer windings have an advantage over single layer windings because of ease in the manufacture of coils and lower cost of winding, less number of coils are required as spare in the case of winding repairs, fractional slot windings can be employed.

5. The single layer windings have higher efficiency and quieter operation because of narrow slot openings?
a) true
b) false

View Answer

Answer: a [Reason:] The single layer winding has a high efficiency and quiet operation because of narrow slot openings. They also have higher space factor owing to the absence of inter layer separator.

6. When is the double layer bar or wave windings made use of?
a) when single turns coils are necessary as with turbo alternators and unipolar low voltage machines
b) when single turns coils are necessary as with turbo alternators and bipolar low voltage machines
c) when single turns coils are necessary as with turbo alternators and multipolar low voltage machines
d) when double turns coils are necessary as with turbo alternators and unipolar low voltage machines

View Answer

Answer: c [Reason:] The double layer bar or wave windings are used when the single turns coils are necessary. They are also made use of with the multipolar low voltage machines.

7. How many factors are related in the selection of the armature slots?
a) 5
b) 6
c) 7
d) 4

View Answer

Answer: b [Reason:] There are 6 factors associated in the selection of the armature slots. They are i) Balanced windings ii) Cost iii) Hot spot temperature iv) Leakage reactance v) Tooth ripples vi) flux density in iron.

8. How is the number of armature slots associated with the armature windings?
a) number of slots should be such that unbalanced winding is obtained
b) number of slots should be such that balanced winding is obtained
c) number of slots should be so low as possible
d) number of slots should be high as possible

View Answer

Answer: b [Reason:] The number of slots should be such that balanced winding is obtained. Balanced windings should be obtained because it may lead to losses and heating effects.

9. How is the number of armature slots associated with the cost factor?
a) small number of slots leads to less cost
b) small number of slots leads to high cost
c) large number of slots leads to high cost
d) large number of slots leads to low cost

View Answer

Answer: a [Reason:] The smaller the number of slots, the less will be the cost. This is because there are fewer coils to wind, form insulate, place into slots, and connect.

10. How is the number of armature slots associated with the hotspot temperature?
a) small number of slots leads to less hotspot temperature
b) small number of slots leads to high hotspot temperature
c) large number of slots leads to high hotspot temperature
d) large number of slots leads to low hotspot temperature

View Answer

Answer: b [Reason:] The small number of slots leads to increase in hotspot temperature. The small number of slots results in bunching of conductors leaving small space for circulation of air.

11. How is the number of armature slots associated with the leakage reactance?
a) small number of slots leads to less leakage reactance
b) small number of slots leads to high leakage reactance
c) large number of slots leads to high leakage reactance
d) large number of slots leads to low leakage reactance

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Answer: a [Reason:] When the number of slots is small the leakage flux is increased. As the leakage flux is increased, the leakage reactance is increased owing to conductors lying near each other.

12. How is the number of armature slots associated with the tooth ripples?
a) tooth ripples are increased, if the number of slots are increased
b) tooth ripples are decreased, if the number of slots are increased
c) tooth ripples are increased, if the number of slots are decreased
d) tooth ripples are decreased, if the number of slots are decreased

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Answer: b [Reason:] The tooth ripples in the field form and the consequent pulsation losses in pole face decrease if a large number of slots are used. Also the waveform of generated voltage is free from ripples.

13. How is the number of armature slots associated with the flux densities in iron?
a) tooth ripples are increased, if the number of slots are increased
b) tooth ripples are decreased, if the number of slots are increased
c) tooth ripples are increased, if the number of slots are decreased
d) tooth ripples are decreased, if the number of slots are decreased

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Answer: a [Reason:] The large number of slots a greater space is taken up by the insulation. This results in the narrower teeth giving flux densities which may go beyond acceptable limits.

14.The value of slot pitch depends upon the voltage of the machine?
a) true
b) false

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Answer: a [Reason:] The value of the slot pitch serves as a guide when choosing the number of armature slots. The value of the slot pitch depends upon the voltage of the machine.

15. What is the value of the slot pitch for the low voltage machines?
a) slot pitch < 25 mm
b) slot pitch = 25 mm
c) slot pitch less than equal to 25 mm
d) slot pitch greater than equal to 25 mm

View Answer

Answer: c [Reason:] The value of the slot pitch depends upon the voltage of the machine. The slot pitch is less than equal to 25 mm for low voltage machines.

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