2011 - content.kopykitab.com€¦ · v) compared to d.c. are welding on a.c. are welding has a)...

7341 [ Turn over

Name : ……………………………………………………………

Roll No. : ………………………………………………………...

Invigilator's Signature : ……………………………………….

CS/B.Tech(EEE)/SEM-7/EEE-704C/2011-12

2011

UTILIZATION OF ELECTRIC POWER

Time Allotted : 3 Hours Full Marks : 70

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own words

as far as practicable.

GROUP – A

( Multiple Choice Type Questions )

1. Choose the correct alternatives for any ten of the following :

10 × 1 = 10

i) For high frequency Eddy current heating, the depth of

penetration is

a) proportional to frequency

b) inversely proportional to frequency

c) proportional to square of frequency

d) inversely proportional to square root of frequency.

ii) Dielectric heating uses

a) high frequency b) low frequency

c) power frequency d) any of a, b, c.


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iii) Some applications of dielectric heating are

a) plywood industry

b) tobacco industry

c) both (a) and (b)

d) none of these.

iv) A direct care type induction motor is suitable for

a) intermittent use

b) continuous use

c) both (a) and (b)

d) none of these.

v) Compared to D.C. are welding on A.C. are welding has

a) lower power consumption but higher efficiency

b) lower power consumption and lower efficiency

c) higher power consumption and lower efficiency

d) higher power consumption and higher efficiency.

vi) Butt welding is a type of

a) resistance welding

b) arc welding

c) atomic hydrogen welding

d) none of these.


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vii) A lamp with a reflector is mounted 10 m above the

centre of a circular area of 20 m diameter. If the

combination of the lamp and the reflector gives a

uniform CP of 800 over the circular area, the minimum

illumination in the area is

a) 4·0 lux b) 2·8 lux

c) 6·0 lux d) None of these.

viii) Sodium vapour lamps use

a) high leakage reactance transformer

b) a capacitor

c) both (a) and (b)

d) none of these.

ix) Typical efficiency of High Pressure Mecury Vapour

lamps lie in the range

a) 80 – 100 lumens/watt

b) 0 – 10 lumens/watt

c) 30 – 40 lumens/watt

d) 100 – 200 lumens/watt.


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x) Types of traction sub-stations depend on

a) nature of the primary supply

b) system of electrification

c) both (a) and (b)

d) none of these.

xi) Smoothing chokes are used in

a) an a.c. locomotive

b) a d.c. locomotive

c) both (a) and (b)

d) none of these.

xii) Electrodiposition typically requires

a) high current and voltage

b) high current and low voltage

c) low current and high voltage

d) low current and low voltages.


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GROUP – B

( Short Answer Type Questions )

Answer any three of the following. 3 × 5 = 15

2. a) Define Luminous Intensity and Luminous Flux. 2

b) An office 25 m × 12 m is illuminated by 40 w in

candescent lamps of 2700 lumens. The average

illumination required at work place is 200 lux. Calculate

the number of lamps required to be fitted in the office.

Assume utilization and depreciation factors are 0·65

and 1·25 respectively. 3

3. Describe the working principle of a mercury vapour lamp. 5

4. Eddy current heating is used for hardening of a steel pulley

and the depth of penetration required is 1·4 mm. The relative

permeability is unity and f = 5 × 10 – 7 Ω m for steel.

Determine the frequency required. 5

5. Why is a d.c. series motor suited for traction ? With the help

of speed-torque characteristics explain how speed can bc

maintained for a d.c. series motor used for traction when the

load increases. 2 + 3

6. Write short notes on the following :

a) arc welding

b) spot welding.


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GROUP – C ( Long Answer Type Questions )


7. A piece of an insulating material is heated by di-electric

heating. The size of the piece is 12 cm ∞ 12 cm ∞ 3 cm. A

frequency of 20 MHz is used and the power obserbed is

450 W. If the material has a relative permitirity of 5 and a

power factor of 0·05 calculate the voltage necessary for

heating and the current that flows in the material. Deduce

any formula used.

8. A low frequency induction furnace operating at 12 V in

secondary circuit takes 480 kW at 0·5 pf when the hearth is

full. If the secondary voltage be maintained at 12 V, estimate

the power absorbed and the power factor when the hearth is

half full ( Assume that the resistance of the secondary halved

and the reactance remains constant ).

What are the disadvantages of vertical care type induction

furnace ? 12 + 3

9. a) What are the requirements of an ideal traction system. 4

b) What are the different systems of railway

electrification ? 3


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c) What are the disadvantages of 25 kV AC traction

system. 3

d) Compare D.C. and A.C. systems of railways

electrification from the point of view of main line and

suburban railway service. 5

10. With the help of circuit diagram explain the working principle

of a fluorescent lamp. What are the normal values of power

factor and power consumption for these lamps. Where are

they most suited ? 10 + 3 + 2

11. a) State Faraday's Laws of Electrolysis. 4

b) Define equivalent weight and valency. 4

c) A sheet having a surface area of 0·36 m 2 is to be

electroplated with copper of thickness 0·0254 mm.

Calculate the quantity of electricity required. ECE of

copper = 32·95 ∞ 10 – 8 kg/c and density of copper is

8900 kg/m 3 . 7

7341 [ Turn over

Name : …………………………………………….………………

Roll No. : …………………………………………...……………..

Invigilator’s Signature : ………………………………………..

CS/B.TECH (EEE)/SEM-7/EEE-704C/2012-13

2012

UTILIZATION OF ELECTRIC POWER Time Allotted : 3 Hours Full Marks : 70


Candidates are required to give their answers in their own words

as far as practicable.

GROUP – A ( Multiple Choice Type Questions )

1. Choose the correct alternatives for the following : 10 × 1 = 10 i) The load power factor using welding transformer

depends on a) arc length b) material to be welded c) type of electrode to be used d) all of these.

ii) Which of the following is not resistance welding ? a) Projection welding b) MIG welding c) Seam welding d) Spot welding.

iii) In induction heating a) heat is produced due to currents induced in the

charge by electromagnetic action b) the resistance of the charge must be low c) magnetic materials can be easily treated in

comparison to non-magnetic material d) all of these.


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iv) The specific energy consumption of an electric traction drive decreases with a) higher acceleration b) lower acceleration c) higher acceleration & retardation d) lower acceleration & retardation.

v) Low frequency operation of ac series motor for traction drive improves I. power factor II. line reactance III. commutation properties IV. starting torque. Which of the following is true ? a) (I) and (II) b) (II) and (III) c) (I) and (III) d) (II) and (IV).

vi) In case of urban series where two consecutive stops are less than 1 km, which of the following is absent ?

a) Braking period b) Coasting period

c) Speed curve running period d) Free running period.

vii) Series parallel control for traction drives is used for a) DC series motor b) DC shunt motor c) AC series motor d) 3-phase induction motor.

viii) Dielectric heating is used in a) plywood industry b) tobacco industry c) both (a) and (b) d) none of these.

ix) Suburban Railways use a) 1500 V dc b) 400 V, 3-ph ac c) 3300 V, 3-ph ac d) 25 kV, 1-ph ac.


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x) In underground traction, the supply system is

a) 500 V to 1000 V dc

b) 25 kV, 50 Hz ac

c) 25 kV, 25 Hz ac.

GROUP – B ( Short Answer Type Questions )

Answer any three of the following 3 × 5 = 15 2. Explain the process of induction heating. What are its

advantages & disadvantages ? 3. Explain the process of electro-deposition. State the factors

which affect the quality of the deposited surface. 4. Define radiation welding. State and explain the types of

radiation welding. 5. What is solid angle ? Define and explain space-height ratio

and depreciation factor. 6. Explain the factors affecting the specific energy consumption

of an electric traction drive. GROUP – C

( Long Answer Type Questions ) Answer any three of the following. 3 × 15 = 45 7. a) Draw the speed time curve and explain free running,

coasting and breaking for suburban lines. b) An electronic train has quadrilateral speed time curve

as follows : i) uniform acceleration from rest of 2 kmphps far. ii) coasting for 50 seconds.

The train moving a uniform gradient of 1%. Tractive resistance is 40 newton per ton rotational inertia effect 10% of dead weight, duration of station stop 15 seconds and overall efficiency of transmission gear and motor as 75%. Calculate for value of its schedule speed and specific energy conservation of run. 7 + 8


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8. a) What factors are required to be considered while designing the lighting scheme.

b) An illumination on the working plane of 75 lux is required in a room 72 m × 15 m in size. The lamps are required to be hung 4 m above the work bench. Assuming a suitable space-height ratio, a utilization factor of 0·5, a lamp efficiency of 14 lumens per watt and a candle power depreciation of 20%, estimate the number, rating and disposition of lamps. 7 + 8

9. a) Explain how a dielectric heating system works. b) How you will choose the voltage and frequency of

dielectric heating ?

c) A plywood board 0·5 × 0·25 × 0·02 meter is to be heated from 25°C to 125°C in 10 minutes by dielectric heating employing a frequency of 20 MHz the power required in this heating process. Assume specific heat of wood 1500 J/kg/°C, weight of wood 600 kg/m3 and efficiency of process 50%. 3 + 5 + 7

10. a) What are the requirements of good street lighting ?

b) A minimum illumination 80 lumens/m2 is required in the factory shed 50 m × 12 m. Calculate the number, the location and wattage of units to be used. Assume that the depreciation factor is 0·8, coefficient of utilization = 0·4, efficiency of lamp unit = 14 lumens / watt.

11. Write short notes on any three of the following : 3 × 5

a) Symmetrical lamp fitting b) ac arc welding c) train resistance d) electro-cleaning e) fluorescent lamp and its connections.

=============

7008 [ Turn over

Name : ……………………………………………………………

Roll No. : ……………………………………………..…………..

Invigilator's Signature : ………………………………………..

CS/B.TECH(EEE)/SEM-7/EEE-702/2011-12

2011

ELECTRICAL MACHINE DESIGNTime Allotted : 3 Hours Full Marks : 70


Candidates are required to give their answers in their own words asfar as practicable.

GROUP – A

( Multiple Choice Type Questions )

1. Choose the correct alternatives for the following :

10 × 1 = 10

i) Power transformer core should be made of

a) H. R. Steel b) C R G O Steel

c) C R N O Steel d) Mumetal.

ii) Laminated core material is used to minimise

a) copper loss b) iron loss

c) eddy current loss d) histeresis loss.

iii) Core flux of a transformer depends on

a) voltage ratio

b) load current

c) load power factor

d) permissible temperature rise.


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iv) Stepped care is used to

a) reduce core loss

b) reduce copper loss

c) reduce cost

d) to reduce efficiencies.

v) Sp magnetic loading is given by

a)PφπD

b)PφπDL

c)Pφ

πD2L

d) P φ only,

( φ → flux/pole P → pole, D → diameter. L – length )

vi) Total electrical loading is given by

a)Iz z

πDL b)Iz z

πD

c) Iz z d) Iz z

πD 2L .

vii) A transformer oil should have

a) low flash point

b) high fire point

c) high thermal conductivity

d) low loss angle.

viii) Skewing of rotor slot of a SQIM is used to

a) reduce harmonic loss

b) avoid crawling

c) avoid logging

d) time harmonic effects.


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ix) Commutator meterial used in d.c. machine is

a) brass

b) electrolytic copper

c) bar drawn electrolytic copper

d) steel.

x) Window space factor is defined as

a) Ac/Aw

b) Aw/Ac

c) Aw/Volume of iron

d) Volume of Cu/voulme of iron.

( Ac & Aw = Area of Cu & Area of iron )

GROUP – B

( Short Answer Type Questions )


2. Why cross-over type coil is used in h.v. winding and its

current rating is limited within 30 ft. ?

3. Why mitre joint is preferred in large transformer

construction ? Why sandwich type winding is used in low

voltage high current application ?

4. Derive output equation of an a.c. machine and discuss the

criteria for selection of Bav and ac.

5. Why depth to width ratio of slot is limited within 2 - 4 for a

d.c. machine ? What happened if minimum no. of

commutator segment is taken lower than EP/15 ?

6. Why L/Y ratio of SQIM limited with in 1 - 2. Discuss the

factor on which L/Y changes.

WBUT Electrical Engineering 7thSemester Previous Year Question Paper

Publisher : Faculty Notes Author : Panel Of Experts

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