Power Systems — Distribution

Transformers — the reason AC won

continues from lesson 1 — values defined earlier in the course stay live here

ELI5: two coils sharing an iron core. The voltage scales with the turns ratio, the current scales inversely, and the power passes through almost untouched. This one device — stepping voltage up and down at will — is why Tesla's AC beat Edison's DC.

N_{ratio} = 20

turns ratio, primary:secondary

V_{prim} := 9600 V

= 9600 V distribution feeder

V_{sec} = \frac{V_{prim}}{N_{ratio}}

= 480 V 480 V at the service entrance

I_{sec} := 200 A

= 200 A load current at the secondary

I_{prim} = \frac{I_{sec}}{N_{ratio}}

= 10 A just 10 A on the feeder side

✓ pass

abs(V_{prim} * I_{prim} - V_{sec} * I_{sec}) < 1 W

power in = power out (ideal transformer)

Real-world hook: the green cylinder on a utility pole and the brick on your laptop charger are both transformers, stepping thousands of volts down to something your devices can use.

Try it yourself: a transformer with a 30:1 turns ratio fed by 7200 V — what is the secondary voltage? (V_sec = V_prim/N.)

Vsec_{you} := 7200 V / 30

= 240 V ✏️ Your turn: divide 7200 V by the turns ratio 30.

✓ pass

abs(Vsec_{you} - 7200 V / 30) < 0.1 V

green when your secondary voltage is correct