West Bengal Institute of Technology (WBIT) 2009 B.Tech Electrical Engineering Power system-i - Question Paper

B.TECH (EE-502), WBUT (2009-10)
SEM-5
POWER SYSTEM-I

Time allotted: three Hours Full Marks: 70

GROUP-A
(Multiple option kind Questions)

1. select the accurate option for any ten of the subsequent : [10X1=10]

i) Corona loss can be decreased by using
a) solid conductor of diameter 'd'
b) hollow conductor of diameter 'd+del(d)'
c) bundle conductor
d) both (a) and (b)
e) both (b) and (c)

ii) Tower footing resistance of a transmission tower should be

a) as high possible b) as low as possible
c) moderately high d) moderately low.

iii) By increasing the transmission voltage double of its original value, the identical power can be dispatched keeping the line loss

a) equal to its original value
b) half of original value
c) double the original value
d) one- 4th of original value.

iv) Characteristics of an overhead line usually in the range of

a) 100 ohms- 200 ohms
b) 200 ohms- 300 ohms
c) 400 ohms- 500 ohms
d) 0 ohm - 100 ohms.

v) The dielectric strength of air under normal condition is about

a) 100 kVp/ cm b) 21.1 kVp/cm c) 30 kVp/cm d) 200 kVp/cm.

vi) A synchronous compensator absorbs inductive reactive power. It is

a) over excited
b) normally excited
c) under excited
d) none of these.

vii) To find the maximum value of stress in cables, the ratio (R/r) should be

a) 2.13 b) 2.718 c) 1.96 d) 1.5

viii) Poll mounted substations are used in

a) primary transmission system
b) secondary transmission system
c) primary distribution system
d) secondary distribution system.

ix) As the load factor of a generation plant increases, the generation cost per kWh generated

a) reduces b) increase c) remains identical d) non of these.

x) In a transmission line having negligible resistance, the surge impedance is

a) sqrt(L+C) b) sqrt(C/L) c) sqrt(1/LC) d) sqrt(L/C).

xi) Transposition of transmission line is done to

a) decrease line loss
b) decrease skin effect
c) balance line voltage drop
d) decrease corona.

GROUP-B

(Short ans kind Questions)

ans any 3 of the subsequent. [3 X 5= 15]

2. explain the effect of wind and ice on sag.

3. What is arcing ground ? How ice can be minimized?

4. discuss the method of capacitance grading of an underground cable.

5. define the subsequent briefly :

a) Pin kind insulator
b) Suspension kind insulator.
c) Post kind insulator.

6. What is a string chart ? What is its utility?

GROUP - C

(Long ans kind Questions)

ans any 3 of the subsequent. [3 X 15=45]


7. a) What is corona? discuss briefly the factors which affect corona.

b) obtain the disruptive critical and visual corona voltage of a grid line operating at 132 kV.The subsequent data is given:

Conductor = 1.9 cm, conductor spacing = 3.81 m, temperature = 44 degree Celsius, barometric pressure= 73.7 cm, conductor surface factor: fine weather = 0.8, rough weather = 0.66.

8. a) Write down the general aspect of power distribution system.

b) A 2-wire D.C. distributor, 800 meter long, is fed from both ends. It is uniformly loaded at the rate of 1.1 A/m run. compute the voltage at the feeding points A and B if the minimum potential of 230 V occurs at point C at a distance of 500 meters from the end A. Resistance of the distributor is 0.1 ohm/km (go and return).

9. What is sag? What factors affects sag? An overhead line erected across a span of 250 meters on level supports. The conductors have a diameter of 1.42 cm and have a dead weight of 1.09 kg/m. The line is subjected to wind pressure of 37.8 kg/ sq. meter of projected area. The radial thickness of ice is 1.25 cm line is carried by insulator string 1.43 km long. Calculate: (i) sag in inclined direction (ii) sag in vertical direction (iii) height of least cross arm to provide minimum ground clearance of 7.62 m under bad weather condition. presume 1 cubic meter of ice weight 913.5 kg and maximum stress of 1050kg/sq. cm.

10. The daily load of an industrial corona is as follows:

100 kW for nine hours, 125 kW for six hours, 50 kW for seven hours, five kW for two hours.

The tariff rate is Rs. 800 per kW of maximum demand per year plus Rs. 2.50 per kWh. Determine the energy consumption per year (365 days) and yearly bill.

11. Write short notes on any 3 of the subsequent :

a) Earthing of substation

b) option of voltage for transmission line

c) Ferranti effect

d) Power circle diagram

e) 2 part tariff.

Earning:   Approval pending.