Question

Your local power company produces 1000 amps at 500 Volts AC and runs it through a step-up transformer to get a line voltage of 750,000 Volts.

What is the resulting current in the line??

What is the ratio of turns between the primary and the secondary of the step-up transformer??(N(primary)/N(secondary))

At the other end of the line there is a step-down transformer with 5000 turns on the primary (the side with 750,000 Volts). How many turns must the secondary have to step the voltage down to 120 Volts?

Answer 1

Well, if a transformer is perfectly efficient, then the total power, in watts, will be the same on both sides of the transformer. watts (power) is equal to current (amps) times voltage (volts). so what's the power going into the first transformer?

Answer 2

so powering going into first transformer is 500000, so the current going out is going to be power(500000)/ voltage(750,000)???

Answer 3

yes, exactly!

Answer 4

ok so what is N?

Answer 5

N is the number of turns in the winding of the transformer. The voltage gets stepped up or down in the same ratio as the ratio between the windings in the transformer. So we don't know exactly how many windings the transfer has, but we know the ratio between them, because we know the ratio between the input and output voltages.

Answer 6

The equation is
\[{V_s\over V_p} = {N_s\over N_p}\] where _s means secondary and _p means primary

Answer 7

so its the same ratio is the input to output voltages?

750000/500000??

Answer 8

You're close - one of those is a voltage and one is a power. The input and output voltages are actually both given as part of the problem.

Answer 9

oh oh ok... is it supposed to be primary over secondary?? thats what the problem says

Answer 10

Right, you can put either one in the numerator, as long as you're consistent. So if they want N_p/N_s, then you compute V_p/V_s. Primary is the input, secondary is the output.

Answer 11

ok gotcha .. let me try to do last part myself i will ask for help if i need

Answer 12

OK, good luck!

Answer 13

so 5000turns/ secondary turns = primary voltage(750000V)/secondary voltage (120V)

making the ratio 4/5 or .8 turns??

is this correct?