Code No:310203

III-B-Tech I-Semester Supplementary Examinations

June-2003
Set No. 2

POWER SYSTEM – II

(Electrical and Electronics Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) What factors must be taken into account while calculating the resistance of Overhead line conductors? How are these factors accounted for?

b) What is equivalent spacing of a 3-phase line ? What is its significance?

c) A 3-phase 50km long single circuit 66KV transposed Overhead line has horizontal spacing with 3meters between adjacent conductors and 6 meters between outer conductors. The conductor diameter is 2 cm. Find the inductance per phase.

2. a) Why transmission line conductors are stranded?

b) Give important application of Bundled and Hollow conductors.

c) Why transmission lines are transposed ? Explain the procedure of transposition.

d) A single phase transmission line has conductors 2cm in diameter spaced 3 meter apart. Calculate the inductance per km of the loop.

3. a) Discus why receiving end voltage of an unloaded lone line may be more than the sending end voltage.

b) A single phase transmission line 100km long has the following constants. Resistance per is 0.25 ohms and reactance per km is 0.8 ohms. Susceptance per km is 14 micro mho. Receiving end voltage is 66KV. Assuming that the total capacitance of the line is localized at the receiving end alone, determine sending end voltage, sending end current, regulation, efficiency and supply power factor. The line is delivering 15MWat 0.8lagging power factor. Draw the vector diagram to illustrate your calculations.

4. a) What is Proximity effect?

b) A 345 KV 3 phase transmission line is 130km long. The resistance per phase = 0.036 ohms/km and inductance per phase is 0.8mH/KM. The shunt capacitance is 0.0112 micro Farad/km. The receiving end load is 270MVA with 0.8power factor lagging at 325KV. Find the voltage and power at the sending end and the voltage regulation. Use
(i) Nominal T method
(ii) Nominal pi method
(iii) ABCD constants.
Compare the result.

5. a) The transmission line is designed based on worst probable conditions and not worst possible conditions. Why?

b) An overhead line has the following data: span length 160metres, conductor dia 0.95cm, weight per unit length of the conductors 0.65kg/meter. Ultimate stress 4,250Kg/cm², wind pressure 40Kg/Cm² of projected area. Factor of safety 5. Calculate sag.

6. a) What is the relation between the conductor diameter and breakdown potential of a cable while voltage of the cable and its overall diameter are fixed? Prove the same.

b) The capacitance per kilometer of a 3-phase belted cable is 0.25microfarsds between the two cores with the third core connected to the lead sheath calculate the charging current taken by five kilometers of this cable when connected to a 3-phase, 50Hz, 11 KV supply.

7. a) List and explain any four disadvantages of low power factor.

b) Derive an expression for most economical power factor for constant KVA- demand.

8. a) Explain the method of improving power factor by using synchronous condenser. Discuss the merits and demerits of the above method.

b) A synchronous motor improves the p.f.of a load of 200KW from 0.8 lagging to 0.9 lagging. Simultaneously the motor carriers a load of 60KW. Find

i) The leading KVAR supplied by the Motor.
ii) The p.f. At which motor operates.