Code No:310203

III-B-Tech I-Semester Supplementary Examinations

November-2002
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) Clearly explain what you understand by GMR and GMD of a transmission line.

b) Derive the expression for inductance per km of a 3 phase line with magnal spacing between the conductors.

c) Calculate the inductance lkmlpn for a 3 phase trans. Orission live with D_ab = D_bc = 4m and D_ca = 8m. The radius of the conductors is 0.25m. The line is transposed.

2. a) What is the effect of low power factor in a system.

b) Clearly explain the use of static capaciters for improvement of power factor. Derive the expression for most economical power factor for constant kw loads.

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

b) A single phase transmission line 100km long has following constants. Resistance per km is 0.25 ohms and reactance per km is 0.8ohms. 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 along, determine sending end voltage. Sending end current, regulation, efficiency and supply power factor. The line is delivering 15 MW at 0.8lagging power factor. Draw the vector diagram to illustrate your calculations.

4. a) Define disruptive critical voltage.

b) A 110KV, 3 phase, 50Hz transformed line , 175km long consists of three 1cm diameter stranded copper conductor spaced in 3m delta arrangement. Temperature taken at 26⁰C and barometric pressure as 74cm. Assume surface irregularity factor m=0.85, (roughness factor) mV for local corona = 0.72 and mV for general corona=0.82. Find
i) Disruptive voltage
ii) Visual corona voltage for local corona
iii) Visual corona voltage for general corona
iv) Power loss due to corona using Peek's formula fair weather and wet conditions
v) Power loss due to corona using Peterson's formula under fair weather and wet conditions.

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

b) A 132KV transmission line uses A.C.S.R. Conductors whose data are; Nomial copper are 110mm², size 30 + 7/2.79mm, weight 844kg/km., ultimate strength 7,950Kg. Calculate the height above ground at which the conductors with a span of 300metrs should be supported, the factor of safety being 2. Wind pressure 75g/m² of projected area. Ground clearance required is 7 metres.

6. A three -phase overhead transmission line is supported on 4 disk suspension insulators. The voltage across the second and third discs are 13.2KV and 18KV respectively. Calculate the line voltage and mention the nearest standard voltage in practice.

7. a) Prove that for a concentric cable of given dimension and given maximum potential gradient in the dielectric, the maximum permissible voltage between core and the sheath is independent of the permittivity of the insulating material.

b) A single core 66KV cable working on 3 phase system has a conductor diameter of 2 an and a sheath of inside diameter 5.5cm. If the two inter sheath are introduced in such a way that the varies between the same maximum and minimum in the three layers find :
i) Positions of inter sheath
ii) Voltage on the inter sheath
iii) Maximum and minimum sheath

8. The capacitances of 3 core cable beltd type are measured and found to be as follows:
a) Between 3 cors bunched together and the sheath 8 micro farad
b) Between conductor and the other two connected together to the sheath 5 micro farads Calculate the capacitance to neutral and the total charging KVA when the cable is connected to a 11 KV. 50kz, 3-phase supply.