Know

Question 1

Star vs. Delta configuration

Answer 1

STAR:
- Speeds of star connected motors are slow as they receive 1/√3 (58%) of the line voltage.
- Lower phase voltage requires lower number of turns (saving in copper).
- Low insulation required as phase voltage is low.
- Typically used in power transmission (long distances where unbalanced loads are not common).
DELTA:
- The speeds of delta connected motors are high because each phase gets the total line voltage.
- Higher phase voltage requires higher number of turns (increase in copper).
- Heavy insulation required.
- Typically used in power distribution and in industries (short distances where unbalanced loads may occur).

Question 2

Critically evaluate whether underground or overhead systems should be used for power transmission and
distribution.

Answer 2

The decision between underground and overhead systems is in principle an economical and an environmental issue.

• Underground systems are in general more reliable than overhead systems, because they are not exposed to wind, lightning and vehicle damage.
• Underground systems do not disturb the environment and they require less preventative maintenance.
• The main disadvantage is its higher costs: for the same power rating: underground systems are in general 6 to 10 times more expensive than overhead systems.

Question 3

Critically decide between aluminium and copper as material of construction in overhead transmission lines.

Answer 3

RESISTIVITY: quantifies how strongly a given material
opposes the flow of electric current.
- The resistivity of copper is only 62% of that of aluminium, which makes copper a better conductor.
DENSITY:
- The copper three times denser than aluminium.

Thus even though copper has 62% the resistivity of aluminium, you will need double the weight in copper to transmit the electricity.

Question 4

CSP

Answer 4

Concentrate Solar Power
Mirrors concentrate the solar energy to the central point. Then some medium is heated, which is used to create steam which turns a turbine, powering a generator that then generates electricity.
Can be used beyond the point of sunset.
Including CSP gives you flexibility in energy mix.