Code No:310203

III-B-Tech I-Semester Supplementary Examinations

November-2002
Set No. 4

POWER SYSTEM – II

(Electrical and Electronics Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. Explain method of images to calculate the capacitance of overhead line taking into account the effect of ground.

2. a) Explain the method of transposition.

b) Calculate the inductance of each conductor in a 3phase, 3 wire system, when the conductors are arranged in a horizontal plane with spacing such that D₁₃ = 4m, D₁₂ = D₂₃ = 2m. The conductors are transposed and each has a diameter of 2.5cm.

3. a) Draw the vector diagram of nominal D and nominal T models.

b) A single phase 50Hz generator supplies an inductive load of 5MW at a power factor 0.707 by means of an overhead line of 20Km long. The line resistance and inductance are 0.0195ohms and 0.63mHper Km respectively. The voltage at the receiving end is to be kept at 10 KV. Find
i) Voltage regulation and ii) Efficiency of the transmission.

4. a) Explain grading methods of string insulators?

b) Each conductor of a 3 phase H.v. Transmission line is separated by a string of 4 insulators. If the potential difference across the second from top is 13.2KV and across 3rd from top is 18KV, determine the voltage between conductor.

5. a) Derive the expression for the sag and tension of an over head transmission line supported by towers of equal heights.

b) A transmission line has a span of 150m between level supports. The cross sectional area of the conductors is 1.25cm² and weight 100kg per 100mt. If the breaking stress is 4220 Kg/cm², calculate the factor of safety if the sag of the line is 3.5 Kg/m².

6. a) Explain 'Corona'.

b) A certain 3 phase equilaterally spaced transmission line conductors has a total corona loss of 53 kw at 106KV and a loss of 98Kw at 110KV. What is the disruptive critical voltage between lines? What is the corona loss at 113KV.

7. a) Discuss the causes of low powerfactor of the supply system.

b) Write short notes on power factor improvement methods.

8. a) Find expressions for capacitance and dielectric stress of a single core cable.

b) Derive expression for power in a 3b phase circuit using symmetrical components.