Khoo Yihan | Chua Cong Yang | Park Seong Jin

 Electricity is generated in power stations at 11000V to 33000V and then stepped up to V by transformers.  V fed into the grid  why so high voltage?  Power from the grid is stepped down in successive stages at substations and distributed to different consumers.

 Electrical power is generally transmitted:  Using alternating current  Very high voltage

 Used because the voltage can be stepped up and down easily, cheaply and efficiently using a transformer  Recall how a transformer works  Stepping up/down of current relies on the change in magnetic flux  Induced current will stop if there is no change (in the case of a DC circuit)  AC will continually ‘open and close’ the circuit by continually changing the magnetic field

 Problem faced: Electrical power from power stations lose power due to the heating effect of current in the grid cables  Heat lost is given by P = VI = I 2 R where I is the transmission current and R is the resistance of the cables.  With high voltage, power lost is minimum.

 To reduce resistance, thick cables can be used (cross-sectional area increases), but this is very uneconomical and heavy to use.  Step up the current in transformers instead

Question: Find the power wasted per km as internal energy in the cable when 10/ MW is transmitted through a cable of resistance 1 Ω per km (a) at 10kV (b) a 200kV

(a) P = VI Transmission current I = P/V = 10 7 W / 10 4 V = 1000 A Power loss per km Ω = I 2 R = (1000) 2 x 1 = 10 6 W This is equivalent to almost 10% of the power generated at the power station

(b) Transmission current I = P/V = 10 7 W/ 2x10 5 V = 50 A Power loss per km = I 2 R = (50) 2 x 1 = 2500 W The power loss would only be about 0.025% of the power generated at the power station