# Homework Help: Physics electric generator potential difference question

1. May 31, 2007

### shanktank

Hi all,
I'm on the final question of an assignment, unforunatly its not really a calculation or anything and i can't find any information on it i thought maybe someone could help me out

13. At a coal-fired electric generating station, heat from the burning coal is used to drive a steam turbine. The turbine drives an electric generator to produce electricity at a potential difference of 1.20 x 10^3 V. The energy is transmitted to a nearby town at a potential difference of 6.60 x 10^5 V. Upon reaching the town the potential difference is reduced to 2.40 x 10^3 V in lines running along the streets and is then reduced to 120 V for home use.

a) Explain why the potential difference is increased to 6.60 x 10^5 V for transmission when it is just going to be decreased to 120 V at the consumers home anyway.

b) what is the ratio of the number of turns required on the secondary to the turns on the primary for the transformer responsible for changing the potential difference from 1.20 x 10^3 V to 6.60 x 10^5 V?

Vp/Vs = Np/Ns
1.20 x 10^3 V/6.60 x 10^5 V = 1/x
x=1/0.1818181818
x= 500 :1

I really need help with the a) part and as far as the b) part i think i went the right direction not positive though. If anyone see's a flaw please do tell. Thankyou all

Shane

2. May 31, 2007

### londonrulz

when the power is to be transmitted to long distances the power losses are taken in to consideration. According to the joules law, the loss(heat) is equal to the square of the current. Hence in order to decrease this heat loss the voltage is increased keeping the power constant and decreasing the current. this might not be the exact wordings but hopefully it explains.

note: the voltage is again decreased for home use, bcos of risk involved with higher voltages.

3. May 31, 2007

### ank_gl

yea londonrulz is correct, losses r low at low currents, so they inc the voltage n dec the current.
n for part b) u went the right direction dude