Question

Question 5. (20 marks). (a) A 10kV power transmission wire is being planned between Adelaide and Sydney (1600km). It should have a resistance of 100 2. The material for the wire must be chosen from the candidates below. Which of the materials is not appropriate? From the remaining materials, determine the most cost effective. (10 marks). Material Yield Thermal Conductivity Density Cost Appropriate stress. Conductivity (Qm). (kg/ (/kg) (Yes/No). (W/mK). m) (MPa) If no, why? Copper. 180 390 1.68 x 10" 8900 $5 Polystyrene 40 0.01. 2 x 10 1300 $0.03. Glass 400 0.8. 3 x 10" 2200 $0.5. Aluminium 100 195 2.65 x 10" 2700 $1.5. .

Answer 1

ANSWER A:

COPPER: copper has a high conductivity and greater tensile strength. Therefore Copper conductors have relatively smaller cross sectional area. Also copper is durable and has high scrap value. However due its higher cost and non availability copper is rarely used for overhead transmission lines.

GLASS: Glass is a very good insulator and was commonly used on power lines. The downside is that it is not the cheapest material that you can find. It is also very heavy . From the given tablr in the question we can understand that glass cannot be used as conductor.

POLYSTYRENE: Polystyrene is used as insulator as it have low thermal conductivity. Also they have small air bubbles trapped inside them. This makes them very good insulator as because heat energy cant flow through them.

ALUMINIUM: After copper aluminium is the best metal used in transmission lines because it has the good thermal conductivity and it is more available than copper and it is cheapest than copper.

Answer b.

COPPER: Copper has the high conductivity where as in insulator it cannot . A good insulator must have good resistance.

EXPANDED POLYSTYRENE: Polystyrene properties and its key benefits made it a great insulator. It has very low thermal conductivity due to its closed cell structure consisting 98% air . This air trapped with in the cells is a very poor heat conductor.

Glass wool. It serves to trap    and prevent its circulation that would transfer heat . It is not flammable. It is cheaper than polystyrene   and can be used in refrigerators.

ALUMINIUM: aluminium is a good thermal conductivity as they have good thermal conductivity.