Question

Give the advantage of AC in long distance power transmission with an illustration.

Answer 1

1. When power is transmitting for long-distance a fraction of power is lost due to joule heating (I²R).
2. This power loss can be tackled either by reducing current i or by reducing resistance R of a transmission line.
3. At the transmitting point, voltage is increased and the current is decreased by a step-up transformer.
4. This reduced current at high voltage reaches the destination without applicable loss.
5. At the receiving point, voltage is decreased and current is increased by step down transformer.

• Example 1:
  2MW power is transmitted at 40Ω with 10 kV voltage
  I = `"P"/"V" = (2 xx 10^6)/(10 xx 10^3)` = 200 A
  Power loss = I² R = (200)² × 40 = 1.6 × 10⁶ W
  % of Power loss = `(1.6 xx 10^6)/(2 xx 10^6) xx 100 % = 80%`
• Example 2:
  When 2MW power at 40 Q is transmitted with 100 kV voltage.
  I = `"P"/"V" = (2 xx 10^3)/(100 xx 10^3)` = 20 A
  Power loss = I² R = (200)² × 40 = 0.016 × 10⁶ W
  % of power loss = `(0.016 xx 10^6)/(2 xx 10^6) xx 100%`
  

  = 0.8 × 100% = 80%