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Multiple choice question for engineering

Set 1

1. What is the consideration for the determination of the diameter of shaft?
a) stiffness
b) voltage
c) current
d) rigidity

View Answer

Answer: c [Reason:] The main aspect for the design of the diameter of the shaft is the stiffness. The diameter of the shaft depends on the stiffness of the machine.

2. What is the meaning of stiffness?
a) ability to transmit the power
b) ability to withstand the weight of the rotor
c) ability to withstand unbalanced magnetic pull
d) ability to withstand the weight of rotor and unbalanced magnetic pull

View Answer

Answer: d [Reason:] The diameter of shaft for an electrical machine is determined by considerations of stiffness. The stiffness is the ability to withstand the weight of rotor and unbalanced magnetic pull.

3. What should be the first property of the shaft design?
a) the shaft design should be such that the shaft must have enough corrosion resistance
b) the shaft design should be such that the shaft must have enough mechanical strength
c) the shaft design should be such that the shaft has enough tensile strength
d) the shaft design should be able to withstand the voltage fluctuations

View Answer

Answer: b [Reason:] The shaft design should be such that the shaft must have enough mechanical strength. The strength should be such that it should withstand all loads without causing much residual strain.

4. What is the second property of the shaft design?
a) the shaft design should be such that it has high rigidity
b) the shaft design should be such that it should have high tensile strength
c) the shaft design should be such that it should have high corrosion resistance
d) the shaft design should be such that it should withstand voltage fluctuations

View Answer

Answer: a [Reason:] The second property of the shaft design such that it should have high rigidity. The rigidity should be such that the deflection of shaft under operation of machine does not reach such a dangerous value as to cause the rotor to touch the stator.

5. The critical speeds of rotation should be different from running speed of machine?
a) true
b) false

View Answer

Answer: a [Reason:] The critical speed relation is the third property of the shaft design. The critical speeds of rotation should be different from the running speed of the machine.

6. What is the formula of the diameter of the shaft?
a) diameter of the shaft = 5.5 + (output in watt/rps)1/3 mm
b) diameter of the shaft = 5.5 – (output in watt/rps)1/3 mm
c) diameter of the shaft = 5.5 * (output in watt/rps)1/3 mm
d) diameter of the shaft = 5.5 / (output in watt/rps)1/3 mm

View Answer

Answer: c [Reason:] The output is first calculated from the operation of the machine. Next the tachogenerator is used to calculate the speed of the machine and on the substitution of the values gives the diameter of the shaft.

7. What is the relation of the diameter of the shaft in the bearings to the diameter under the armature?
a) diameter of the shaft is very much greater than the diameter under the armature
b) diameter of the shaft is greater than the diameter under the armature
c) diameter of the shaft is equal to the diameter under the armature
d) diameter of the shaft is lesser than the diameter under the armature

View Answer

Answer: d [Reason:] There are certain rules in the design of the shaft. The diameter of the shaft in the bearings is less than the diameter under the armature.

8. What happens when the diameter under armature is 150 mm or above?
a) diameter of the shaft in bearing is 100 mm smaller than the maximum diameter
b) diameter of the shaft in bearing is 90 mm smaller than the maximum diameter.
c) diameter of the shaft in bearing is 70 mm smaller than the maximum diameter.
d) diameter of the shaft in bearing is 50 mm smaller than the maximum diameter.

View Answer

Answer: d [Reason:] The diameter of the shaft in the bearings is less than the diameter under the armature. The diameter of the shaft in bearing is 50 mm smaller than the maximum diameter.

9. What happens in the case of the small shafts?
a) the diameter in the bearings should be about 1/3 of the maximum diameter
b) the diameter in the bearing should be about 2/3 of the maximum diameter
c) the diameter in the bearing should be about 2/5 of the maximum diameter
d) the diameter in the bearing should be about 1/5 of the maximum diameter

View Answer

Answer: b [Reason:] The diameter of the shaft in the bearings is less than the diameter under the armature. The diameter in the bearing should be 2/3 of the maximum diameter.

Set 2

1. How is he reluctance motor with respect to synchronous motor and are the field windings?
a) small synchronous motor with field windings
b) small synchronous motor without field windings
c) large synchronous motor with field windings
d) large synchronous motor without field windings

View Answer

Answer: b [Reason:] Reluctance motor is nothing but a simple small synchronous motor with salient pole rotor. They are without field windings in which the field flux is produced.

2. Why is the three phase reluctance motor preferred over single phase reluctance motor?
a) single phase reluctance motors have the phenomenon of hunting
b) single phase reluctance motors have the phenomenon of over voltage
c) single phase reluctance motors have high losses
d) single phase reluctance motors have low output

View Answer

Answer: a [Reason:] The reluctance motor is a small synchronous motor with salient pole rotor. The single phase reluctance motors have the phenomenon of hunting.

3. What is the relation of the input voltage with the magnetic flux?
a) if the input voltage is constant, the magnetic flux increases
b) if the input voltage is constant, the magnetic flux decreases
c) if the input voltage is constant, the magnetic flux is constant
d) if the input voltage is constant, the magnetic flux is zero

View Answer

Answer: c [Reason:] The input voltage is given constant, which results in the constant magnetic flux. The magnetic flux is independent of the excitation.

4.What is the power factor in the reluctance motor and the range of efficiency?
a) leading power factor, 60-75%
b) lagging power factor, 50-75%
c) zero power factor, 55-80%
d) lagging power factor, 55-75%

View Answer

Answer: d [Reason:] The power factor in the reluctance motor is lagging power factor. The efficiency of the machine is about 55-75%.

5. What is the angle at which the electromagnetic torque is maximum?
a) 300
b) 450
c) 600
d) 900

View Answer

Answer: b [Reason:] The electromagnetic torque is maximum at the angle of 450. The range of operation of the reluctance motor lies in the range of 0-450.

6. What is the range of the ratio of the direct axis reactance to the quadrature axis reactance?
a) 1.5-2.3
b) 1.6-2.7
c) 1.6-2.2
d) 1.2-2.0

View Answer

Answer: c [Reason:] The minimum value of the ratio of the direct axis reactance to the quadrature axis reactance is 1.6. The maximum value of the ratio of the direct axis reactance to the quadrature axis reactance is 2.2.

7. How many design dimension are present in the design of the small reluctance motor?
a) 3
b) 4
c) 5
d) 6

View Answer

Answer: c [Reason:] There are 5 design dimensions present in the design of the small reluctance motors. They are the design of the main dimensions, design of stator windings, design of the rotor of the reluctance motor, design of performance parameters, design of losses and efficiency.

8. What is the range of the constant used in the calculation of the active power of reluctance motor?
a) 0.3-0.4
b) 0.35-0.55
c) 0.40-0.50
d) 0.35-0.60

View Answer

Answer: b [Reason:] The minimum value of the range of the constant used in the calculation of the active power of reluctance motor is 0.35. The maximum value of the range of the constant used in the calculation of the active power of reluctance motor is 0.55.

9. How many steps are present in the calculation of the determination of main dimensions?
a) 5
b) 4
c) 3
d) 2

View Answer

Answer: a [Reason:] There are 5 steps present in the calculation of the determination of main dimensions. They are electromagnetic power of reluctance motor, output coefficient, pole pitch, pole arc, peripheral velocity.

10. How many steps are present in the calculation of the design of stator windings?
a) 10
b) 11
c) 9
d) 12

View Answer

Answer: b [Reason:] There are 11 steps involved in the calculation of the design of stator windings. They are input current to motor, number of stator slots, stator winding pitch, winding factor, useful flux, number of turns per stator winding, cross sectional area of the stator winding, slot area, mean length for conductor, active resistance of stator winding, specific permeance of leakage flux.

11. How many steps are present in the calculation of the design of rotor of reluctance motors?
a) 4
b) 5
c) 3
d) 2

View Answer

Answer: a [Reason:] There are 4 steps involved in the design of rotor of reluctance motor. They are rotor diameter calculation, height of rotor core, mmf for magnetic circuit, saturation coefficient of motor.

12. How many steps are involved in the design of performance parameters?
a) 6
b) 5
c) 7
d) 8

View Answer

Answer: c [Reason:] There are 7 steps involved in the design of the performance parameters. They are no load current, height of steel stator teeth, weight of steel in the stator core, copper loss in the stator winding under no load, active resistance and leakage reactance, active component of no load current, starting torque of 3 phase reluctance motor.

13. How many design steps are involved in the determination of the losses and efficiency?
a) 2
b) 3
c) 4
d) 5

View Answer

Answer: b [Reason:] There are 3 steps involved in the determination of the losses and efficiency. They are copper loss in stator winding, iron loss in stator steel, mechanical loss in the motor.

14. What is the formula for the slot pitch factor in design of rotors?
a) slot pitch factor = 3.14*rotor diameter*number of rotor slots
b) slot pitch factor = 3.14/rotor diameter*number of rotor slots
c) slot pitch factor = 3.14*rotor diameter/number of rotor slots
d) slot pitch factor = 1/3.14*rotor diameter*number of rotor slots

View Answer

Answer: c [Reason:] First the rotor diameter and the number of rotor slots are first calculated. On substitution the slot pitch factor can be obtained.

15. The active resistance of the stator winding is calculated at the temperature of 450 C?
a) true
b) false

View Answer

Answer: b [Reason:] The active resistance of the stator winding determination is one of the steps in the design of stator windings. The value is calculated at the temperature of 450 C.

Set 3

1. What type is the stator windings of the single phase induction motor?
a) hollow
b) cylindrical
c) concentric
d) rectangular

View Answer

Answer: c [Reason:] The stator windings are also known as the running winding or the main winding. The type of stator winding used is concentric type

2. How many coils are present in the stator windings?
a) 2
b) 3
c) 2 or more
d) 3 or more

View Answer

Answer: d [Reason:] The stator windings of single phase induction motors are concentric type. There are usually 3 or more coils per pole each having same or different number of turns.

3. How much of the total slots are used for the reduction of the mmf wave harmonics?
a) 60%
b) 65%
c) 70%
d) 80%

View Answer

Answer: c [Reason:] 70% of the total slots are used for the reduction of the mmf wave harmonics. The remaining 30% are used for accommodating the starting windings.

4.How can the small single phase motor reduce the harmonics still much further?
a) removing the winding
b) insulating the winding
c) grading the winding
d) shading the winding

View Answer

Answer: c [Reason:] 70% of the total slots are used for the reduction of the mmf wave harmonics. The mmf wave harmonics can be still further reduced by grading the winding.

5. What is the formula for the mean pitch factor?
a) mean pitch factor = pitch factor of each coil per pole group + turns in the coil / total number of turns
b) mean pitch factor = pitch factor of each coil per pole group / turns in the coil * total number of turns
c) mean pitch factor = pitch factor of each coil per pole group * turns in the coil * total number of turns
d) mean pitch factor = pitch factor of each coil per pole group * turns in the coil / total number of turns

View Answer

Answer: d [Reason:] The pitch factor of each coil per pole group, turns in the coil and total number of turns are obtained. On substitution it gives the mean pitch factor.

6. What is the range of the winding factor for the usual windings distribution?
a) 0.70-0.80
b) 0.75-0.85
c) 0.70-0.85
d) 0.70-0.75

View Answer

Answer: b [Reason:] The minimum value of the winding factor of the usual winding distribution is 0.75. The maximum value of the winding factor of the usual winding distribution is 0.85.

7. What is the formula of the maximum flux in the running winding?
a) maximum flux = flux * pole
b) maximum flux = flux/pole
c) maximum flux = flux / turns
d) maximum flux = flux * turns

View Answer

Answer: b [Reason:] First the flux is calculated along with the number of poles used. On substituting the values the maximum flux value is obtained.

8. What is the value of the stator induced voltage with respect to the supply voltage?
a) stator induced voltage = 95% of supply voltage
b) stator induced voltage = 90% of supply voltage
c) stator induced voltage = 85% of supply voltage
d) stator induced voltage = 80% of supply voltage

View Answer

Answer: a [Reason:] The winding factor is assumed to be 0.75-0.85 for the running winding. The stator induced voltage is 95% of the supply voltage.

9. How many design data are present in the design of the stator?
a) 6
b) 7
c) 8
d) 9

View Answer

Answer: c [Reason:] There are 8 design data available in the design of the stator. The design data are running winding, number of turns In running winding, running winding conductors, number of stator slots, size of stator slot, stator teeth, stator core, length of mean turn.

10. What is the range of the current density for the open type motors split phase, capacitor and repulsion start motors?
a) 4-5 A per mm2
b) 3-4 A per mm2
c) 2-4 A per mm2
d) 1-4 A per mm2

View Answer

Answer: b [Reason:] The minimum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 3 A per mm2. The maximum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 4 A per mm2.

11. What is the relation of the number of slots with the leakage reactance?
a) small number of slots, high leakage reactance
b) large number of slots, high leakage reactance
c) large number of slots, small leakage reactance
d) small number of slots, small leakage reactance

View Answer

Answer: c [Reason:] The number of slots is indirectly proportional to the leakage reactance. The larger the number of slots, the lower will be the leakage reactance.

12. What is the formula for the area required for the insulated conductors?
a) area required for the insulated conductors = total number of conductors per slot * 0.785 / diameter of insulated conductor2
b) area required for the insulated conductors = total number of conductors per slot / 0.785 * diameter of insulated conductor2
c) area required for the insulated conductors = total number of conductors per slot * 0.785 * diameter of insulated conductor2
d) area required for the insulated conductors = 1/total number of conductors per slot * 0.785 * diameter of insulated conductor2

View Answer

Answer: c [Reason:] The total number of conductors per slot and the diameter of insulated conductors are calculated. On substitution the area required for the insulated conductors are calculated.

13. The flux density of the high torque machines is 1.8 weber per m2?
a) true
b) false

View Answer

Answer: a [Reason:] The flux density of the general purpose machine is 1.45 weber per m2. The flux density of the high torque machines is 1.8 weber per m2.

14. The flux density of the stator core should not exceed 1.3 weber per m2?
a) true
b) false

View Answer

Answer: b [Reason:] The flux density of the stator core should not exceed 1.5 weber per m2. The range lies between 0.9 – 1.4 weber per m2.

15. What is the formula for the flux density in stator core?
a) flux density in stator core = maximum flux / length of the iron * depth of stator core
b) flux density in stator core = maximum flux * length of the iron * depth of stator core
c) flux density in stator core = maximum flux / 2 *length of the iron * depth of stator core
d) flux density in stator core = maximum flux * length of the iron / depth of stator core

View Answer

Answer: c [Reason:] The maximum flux, length of iron and depth of stator core is calculated. On substitution it provides the flux density in stator core.

Set 4

1. How many design steps are present in the design of PMDC motors?
a) 8
b) 9
c) 10
d) 11

View Answer

Answer: d [Reason:] There are 11 steps involves in the design of the PMDC motors. They are minimum sum of air gap volume and magnet volume, ratio of magnetic to electric loading, area of magnet, length of magnet, value of flux, number of turns per coil, running armature resistance, armature diameter, axial dimensions, wire cross section and radial thickness.

2. What happens to the armature diameter and the volume of air gap and magnet when the angle is lower in value?
a) volume of air gap and magnet increases, armature diameter increases
b) volume of air gap and magnet increases, armature diameter decreases
c) volume of air gap and magnet decreases, armature diameter decreases
d) volume of air gap and magnet decreases, armature diameter increases

View Answer

Answer: d [Reason:] The lower values of angle, reduces the volume of air gap and magnet. The reduction of volume of air gap and magnet, increases the armature diameter.

3. What should be the range of the product of the magnetic field and magnetic flux density?
a) 4-4.5 * 106
b) 4-4.3 * 106
c) 4.3-4.6 * 106
d) 4.2-4.5 * 106

View Answer

Answer: c [Reason:] The product of the magnetic field and magnetic flux density has a minimum value of 4.3 * 106. The product of the magnetic field and magnetic flux density has a minimum value of 4.6 * 106.

4.What should be the minimum value of the ratio of the magnetic to electric loading?
a) 40
b) 30
c) 50
d) 60

View Answer

Answer: c [Reason:] The calculation of the ratio of the magnetic to electric loading is the second step in the design of the PMDC motors. It should have a minimum value of 50.

5. What is the formula for the area of the magnet in the design of PMDC motors?
a) area of magnet = flux * 4.95 * residual flux density
b) area of magnet = flux / 4.95 * residual flux density
c) area of magnet = flux * 4.95 / residual flux density
d) area of magnet = 1/flux * 4.95 * residual flux density

View Answer

Answer: b [Reason:] First the residual flux density is calculated. Next the flux is calculated and substitution in the formula gives the area of magnet.

6. What is the range of length of the magnet in the PMDC motors?
a) 2.5-4 cm
b) 2-3 cm
c) 2.5-3 cm
d) 1.5-4 cm

View Answer

Answer: a [Reason:] The minimum value of the length of the magnet in the PMDC motor is 2.5 cm. The maximum value of the length of the magnet in the PMDC motor is 4 cm.

7. What is the formula of the length of the magnet?
a) length of the magnet = sum of the volume of air gap and magnet * Area of the magnet + 0.06
b) length of the magnet = sum of the volume of air gap and magnet / Area of the magnet + 0.06
c) length of the magnet = sum of the volume of air gap and magnet / Area of the magnet – 0.06
d) length of the magnet = sum of the volume of air gap and magnet * Area of the magnet – 0.06

View Answer

Answer: c [Reason:] The sum of the volume of the air gap and magnet is first calculated. Next the area of the magnet is calculated from its formula and on substitution gives the length of the magnet.

8. What is the relation between the flux and the no local speed?
a) flux is directly proportional to the no local speed
b) flux is indirectly proportional to the no local speed
c) flux is directly proportional to the square of the no local speed
d) flux is indirectly proportional to the square of the no local speed

View Answer

Answer: b [Reason:] The calculation of the flux value is one of the design steps. The flux is indirectly proportional to the no local speed calculated.

9.What is the formula of the number of turns per coil?
a) number of turns per coil = number of conductors/2*coils/slot*number of armature teeth
b) number of turns per coil = number of conductors*2*coils/slot*number of armature teeth
c) number of turns per coil = number of conductors*2*coils/slot/number of armature teeth
d) number of turns per coil = number of conductors/2*coils/slot/number of armature teeth

View Answer

Answer: a [Reason:] The number of conductors is calculated along with the coils per slot is calculated. Next the number of armature teeth is calculated, and on substitution gives the number of turns per coil.

10. What is the formula for the armature resistance?
a) armature resistance = running armature resistance / 1.0 to 1.0
b) armature resistance = running armature resistance * 1.3 to 1.5
c) armature resistance = running armature resistance * 1.4 to 1.5
d) armature resistance = running armature resistance / 1.3 to 1.3

View Answer

Answer: d [Reason:] The running armature resistance is first calculated in the PMDC motor. It is divided by 1.3 and that gives the armature resistance of the machine.

11. What is the relation between axial dimension and the area of the magnet?
a) area of the magnet is directly proportional to the axial dimension
b) area of the magnet is indirectly proportional to the axial dimension
c) area of the magnet is directly proportional to the square of the axial dimension
d) area of the magnet is indirectly proportional to the square of the axial dimension

View Answer

Answer: a [Reason:] The calculation of the axial dimension is one of the steps in the PMDC motors. The axial dimension is directly proportional to area of the magnet.

12. What is the relation of the wire cross-section with respect to the armature resistance?
a) wire section is directly proportional to the armature resistance
b) wire section is indirectly proportional to the armature resistance
c) wire section is directly proportional to the square of the armature resistance
d) wire section is indirectly proportional to the square of the armature resistance

View Answer

Answer: a [Reason:] The 10th design step of the PMDC motor is the calculation of the wire cross section. The wire cross section is directly proportional to the armature resistance.

13. The radial thickness of the joke directly proportional to the flux?
a) true
b) false

View Answer

Answer: a [Reason:] The last design step in the PMDC motor is the calculation of the radial thickness of the joke. The flux value is directly proportional to the radial thickness of the joke.

14.The radial thickness of the joke is directly proportional to the length of the stator slots?
a) true
b) false

View Answer

Answer: b [Reason:] The last design step in the PMDC motor is the calculation of the radial thickness of the joke. The radial thickness of the joke is indirectly proportional to the length of the stator slots.

15. What is the formula of the length of the stator slots?
a) length of the stator slots = 2 * perimeter of one magnet
b) length of the stator slots = 1/2 * perimeter of one magnet
c) length of the stator slots = 1/3 * perimeter of one magnet
d) length of the stator slots = 3 * perimeter of one magnet

View Answer

Answer: b [Reason:] The length of the stator slots is required in the calculation of the radial thickness of the joke. The length of the stator slots is equal to half the perimeter of one magnet.

Set 5

1. What is the usage of the tanks with tubes?
a) if the temperature rise with plain tank is very low
b) if the temperature rise with plain tank is very high
c) if the temperature rise is zero
d) if the temperature rise with plain tank exceeds the specific limits

View Answer

Answer: d [Reason:] Temperature rise in transformers is calculated with plain walled tanks. If the limits is exceeded then the plain walled tank is replaced by tank with tubes.

2. What is the relation of the provision of tubes with respect to dissipation of heat?
a) the provision of tubes is directly proportional to the dissipation of heat
b) the provision of tubes is indirectly proportional to the dissipation of heat
c) the provision of tubes is directly proportional to square of the dissipation of heat
d) the provision of tubes is indirectly proportional to square of the dissipation of heat

View Answer

Answer: b [Reason:] The provision of tubes increases the dissipating area. The increase in dissipation of heat is not proportional to area because tube screen some of the tank surface preventing radiation from there.

3. What is the relation of the transformer surface with respect to dissipation of heat?
a) transformer surface has no relation with respect to dissipation of heat
b) transformer surface has minor changes with respect to dissipation of heat
c) transformer surface has major changes with respect to dissipation of heat
d) transformer surface has no change with respect to dissipation of heat

View Answer

Answer: d [Reason:] When the tanks with tubes are provided, the dissipation of heat increases. The dissipation of heat has no effect on the transformer surface.

4.How is the circulation of oil improved in tanks with tubes?
a) it can be improved by using dissipating heat
b) it can be improved by using more effective air circulation
c) it can be improved by using more effect power flow
d) it can be improved by using more effective heads of pressure

View Answer

Answer: d [Reason:] The circulation of oil is improved in tanks with tubes. It takes place with the help of using more effective heads of pressure.

5. An addition of 35 per cent should be made to tube area of the transformers?
a) true
b) false

View Answer

Answer: a [Reason:] An addition of 35 per cent should be made to tube area of the transformer. This should be done in order to take into account this improvement in dissipation of loss by convection.

6. What is the loss dissipated by tubes by convection, given area of the tubes = 3.5?
a) 12.3 W per 0c
b) 2.51 W per 0c
c) 5.3 W per 0c
d) 30.8 W per 0c

View Answer

Answer: d [Reason:] Loss dissipated by tubes by convection = 8.8 * Area of tubes Loss = 8.8 * 3.5 = 30.8 W per 0c.

7. What is the formula for temperature rise with tubes?
a) temperature rise with tubes = total loss / dissipating surface*(12.5 + 8.8x)
b) temperature rise with tubes = total loss * dissipating surface*(12.5 + 8.8x)
c) temperature rise with tubes = total loss / dissipating surface / (12.5 + 8.8x)
d) temperature rise with tubes = total loss + dissipating surface*(12.5 + 8.8x)

View Answer

Answer: a [Reason:] The total losses in the transformers are obtained firstly the iron loss and copper loss. Next the dissipating surface temperature is obtained and substituting in the above formula gives the temperature rise.

8. What is the formula for number of tubes?
a) number of tubes = (1/ 8 * area of each tube) * (total loss / temperature rise with tubes – 12.5 * dissipating surface)
b) number of tubes = (1* 8 * area of each tube) * (total loss / temperature rise with tubes – 12.5 * dissipating surface)
c) number of tubes = (1/ 8 * area of each tube) / (total loss / temperature rise with tubes – 12.5 * dissipating surface)
d) number of tubes = (1/ 8 * area of each tube) + (total loss / temperature rise with tubes – 12.5 * dissipating surface)

View Answer

Answer: a [Reason:] First the temperature rise with tubes is obtained. Then the iron loss and copper loss are obtained and added. Area of each tube is also obtained. Substituting all the values in the above formula provides the number of tubes.

9. What is the range of the diameter of the tubes used?
a) 50-60 mm
b) 60-70 mm
c) 70-80 mm
d) 50-70 mm

View Answer

Answer: d [Reason:] The minimum value of the diameter of tubes is derived to be around 50 mm. The maximum value of the diameter of tubes should be less than 70 mm.

10. Elliptical tubes with pressed radiators are increasingly been used?
a) true
b) false

View Answer

Answer: a [Reason:] Elliptical tubes with pressed radiators are on high demand now a days. This is because they give a greater dissipating surface for the small volume of oil.

11. What is the formula for width of the tank for single phase transformers used?
a) width of tank = 2*distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank
b) width of tank = distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank
c) width of tank = 2*distance between adjacent limbs * external diameter of h.v windings + 2*clearance between h.v windings and tank
d) width of tank = distance between adjacent limbs * external diameter of h.v windings + 2*clearance between h.v windings and tank

View Answer

Answer: b [Reason:] Width of tank = 2*distance between adjacent limbs + external diameter of h.v windings + 2*clearance between h.v windings and tank is the formula for three phase transformer. For single phase transformers, the distance between adjacent limbs is not multiplied.

12. What is the formula for the length of the tank?
a) length of the tank = external diameter of h.v winding + clearance on each side between the winding and tank along the width
b) length of the tank = external diameter of h.v winding * clearance on each side between the winding and tank along the width
c) length of the tank = external diameter of h.v winding + 2*clearance on each side between the winding and tank along the width
d) length of the tank = external diameter of h.v winding / 2*clearance on each side between the winding and tank along the width

View Answer

Answer: c [Reason:] The external diameter of h.v winding is obtained. Next the clearance on each side between the winding and tank along the width is calculated and is substituted in the above formula.

13. What is the formula for height of transformer tank?
a) height of transformer tank = Height of transformer frame + clearance height between the assembled transformer and tank
b) height of transformer tank = Height of transformer frame * clearance height between the assembled transformer and tank
c) height of transformer tank = Height of transformer frame / clearance height between the assembled transformer and tank
d) height of transformer tank = Height of transformer frame – clearance height between the assembled transformer and tank

View Answer

Answer: a [Reason:] Firstly, the height of the transformer frame is calculated. Next, the clearance height between the assembled transformer and tank is also calculated. Substitute the values to obtain the height of transformer tank.

14. What is the rating of the transformer for the voltage of about 11 kV?
a) 1000-2000 kVA
b) 100-3000 kVA
c) 1000-5000 kVA
d) 100-500 kVA

View Answer

Answer: c [Reason:] The minimum value of the rating of the transformer for a voltage of about 11 kV should be 1000 kVA. The maximum value of the rating of the transformer for a voltage of about 11 kV should be about 5000 kVA.

15. What is the rating of the transformer for the voltage of above 11 kV upto 33 kV?
a) 1000-5000 kVA
b) less than 1000 kVA
c) above 1000 kVA
d) 100-500 kVA

View Answer

Answer: b [Reason:] 1000-5000 kVA is the rating of the transformer for the voltage of about 11 kV. When the voltage rating is about 11-33 kV, then the rating of the transformer is less than 1000 kVA.