1) A dc 2-wire distributor AB is 500m. long and is fed at both ends at 240V. The loads of 100 A and 60 A are tapped from C and D that are at the distance of 100m. and 250m. from point A respectively. The last 200m. (near end B) is loaded uniformly at the rate of 1 A/m. The resistance of (both go and return) the distributor is 0.001 ohm per metre. Determine
a) the point of minimum potential and its value.
2) An electric train runs between two two substations 6 km. apart maintained at voltages 600 V and 590 V respectively and draws a constant current of 300 A while ion motion. The track resistance of go and return path is 0.04 ohm/km. Determine:
a) The point of minimum potential along the track
b) Currents supplied by the two substations when the train is at the point of minimum potential
3) a) Deduce an expression for the critical disruptive voltage?
b) A 3-phase line has conductors 2 cm. in diameter spaced equilaterally 1m. apart. If the dielectric strength of air is 30 kV (max) per cm, determine the disruptive critical voltage for the line. Consider air density factor δ = 0/952 and irregularity factor m0 = 0.9
4) Write a brief notes over:
a) Skin effect
b) ACSR conductors
c) Corona discharge
5) Describe the voltage control of transmission line by:
a) Tap-changing transformers
b) Synchronous condenser
c) Induction regulators
6 ) A 3-phase transmission line 200 km long has the following constants:
Resistance/phase/km = 0.16 ohm
Reactance/phase/km = 0.25 ohm
Shunt admittance/phase/km = 1.5 * 10-6 S
Find by rigorous method, the sending end voltage and current when the line is delivering a load of 20 MW at 0.8 p.f. lagging. The receiving end voltage is kept constant at 110 kV.
7) A single core 66 kV cable working on the 3-phase system has a conductor diameter of 2 cm. and a sheath of inside diameter 5.3 cm. If two inter sheaths are introduced in such a way that the stress varies between the same maximum and minimum in the three layers, determine:
a) Positions of inter sheaths
b) Voltage on the inter sheaths
c) Maximum and minimum stress
8) Derive an approximate expression for sag in overhead lines when supports are at equal levels
9) a) Explain what is meant by the lightning? Explain the mechanism of lightning discharge.
b) Explain the different types of the lightning stroke
10) Explain what is Arc suppression coil grounding.