Code No:310203

III-B-Tech I-Semester Regular Examinations

November-2003
Set No. 1

POWER SYSTEM – II

(Electronics and Instrumentation Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) Write a short notes on the following types of over head line conductors
i) ACSR ii) Bundled conductors
iii) Hollow conductors iv) AAC conductors.

b) Find the loop inductance and reactance per km of a single phase overhead line consisting of two conductors, each 1.2cm diameter. The spacing between conductors is 1.25meters and frequency is 50Hz.

2. a) Derive an expression for line to neutral capacitance for a 3- phase line when conductors are symmetrical placed

b) What is transposition? Explain the method of transposition of 3-phase line over the lengths.

3. a) Discuss why equivalent π circuit of a long line is preferred over the equivalent T circuit.

b) A three phase 50 Hz transmission line is 150km long and delivers 25MW at 0.85 power factor lagging and at 110KV. The resistance and reactance of the line per conductor per km are 0.3 ohms and 0.9ohms respectively. The line charging admittance is 0.3 x 10^-6 mho per km per phase. Compute by applying the nominal π the voltage regulation and transmission efficiency.

4. In a 5 insulator disc string capacitance between each unit and earth is 1/6 of the mutual capacitance. Find the voltage distributions across each insulator in the string as percentage of voltage of the conductor to earth. Find string efficiency. How is this efficiency affected by rain.

5. a) Derive the expressions for sag and tension when the supports are at unequal heights.

b) A transmission line conductor having a dia of 19.5mm weighs 0.85kg/m. The span is 275meters. The wind pressure is 40 kg/m² of projected area with ice coating of 13mm. The ultimate strength of the conductor is 8000kg. Calculate the maximum sag, if the factor of safety is 2 and ice weighs 910kg/m³.

6. a) With a neat diagram. Show the various parts of a high voltage single core cable.

b) Find the diametral dimensions for the 1-core, metal-sheathed cable giving the greatest economy of insulating material for a working voltage of 85kv,if a dielectric stress of 60 kv per cm be allowed.

7. a) Explain the concept of power factor.

b) Explain any three causes of low power factor of supply system.

c) Discuss the disadvantages of low power factor and list methods to improve power factor.

8. a) What is per unit system? Why it is required in power system calculations? Explain how base values can be selected in the formula for base values can be selected in the network containing transformer.

b) Derive the formula for base impedance

c) By choosing the rating of Transformer as base values, convert all electrical quantities of the following transformer in p.u. Values. Transformer is rated as 100KVA, 2000/200V, single phase has equivalent impedance referred to HV side as (1+j1) ohm and exciting current referred to LV side is 3 Amps.