Code No:310203

III-B-Tech I-Semester Regular Examinations

May/June-2004
Set No. 2

POWER SYSTEM – II

(Electronics and Instrumentation Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. (a) Clearly explain what do you understand by GMR and GMD of a transmission line?

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

(C) Calculate the inductance of each conductors in a 3-phase, 3-wire system, when the conductors are arranged in a horizontal with spacing such that D_RY=4m; D_YB=3m; D_BR=2m. The conductors are transposed and each has a diameter of 2.5cm.

2. What do you understand by electric potential? Derive an expression for electrical potential and hence deduce the formula for capacitance for the following cases:

a) Single phase 2-conductor line

b) 3-phase unsymmetrical spacing, but transposed.

3. 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 0.8 power factor lagging at 325KV. Find the voltage and power at the sending end and the voltage regulation. Use (i) nominal π method (ii) ABCD constants. Compare the result.

4. In a string of 3 suspension insulators capacitance may be represented as shown in figure. (capacitance C₁ being due to guard ring). Find the voltage across each disc as a percentage of total and the string efficiency. Given C¹ and C₁ = 6.06C.

DIAGRAM

5. a) Describe the vibration of power conductors and explain the methods udsed to damp these vibrations.

b) An overhead line at river crossing is supported from two towers of heights 30 metres and 90 metres above water level with a span of 300 metres. The weight of the conductors 1 Kg/metre and the working tension is 2000 Kg. Determine thr clearance between the conductor and the water level midway between the towers.

6. a) Enumerate the advantages of overhead lines compared to UG cables for transmission of very high voltages.

b) A single core cable has a conductor diameter of 2.5cm and a sheath of inside diameter of 6cm. Calculate the maximum stress. It is desired to reduce the maximum stress by using two intersheaths. Determine their best position, the maximum stress and the voltage on each; system voltage is 3- phase 66kv.

7. Explain in detail the following methods of improving power factor. Discuss the merits and demerits of each of the methods:
a) State capacitor b) Synchronous condenser

8. a) A set of unbalanced vectors can be transformed into three sets of balanced components . Explain how this can be done using symmetrical components in detail.

b) A system of unbalanced three phase voltages are given by 100V, +j200V and (-100-j160)V. Determine the three symmetrical components of the system.