Calculating Input Voltage of a Step Down Transformer

[ilovejava]

Homework Statement

A pair of power transmission lines each have 0.68-Ω resistance and carry 650 Amp. If the primary voltage of the 10:1 step-up transformer is 4.6 kV, calculate the input voltage of the step-down transformer at the other end.

Homework Equations

P=IV
V=IR
I_pV_p = I_sV_s

The Attempt at a Solution

I recognized that when the current passes through the primary transformer it will increase, so I used V = IR and rearranged to I = V/R = (4600)/(2(0.68)) = 3382.35A I don't know how to proceed afterwards because if I try to solve for voltage I receive 4600 which is equal to the primary transformer, and cannot be the case because this is a step down transformer.

 

[kuruman]

You have not used the given 10:1 step up ratio.

 

[ilovejava]

You have not used the given 10:1 step up ratio.

So you mean to tell me that the primary transformer has 10 turns and the secondary has 1 turn? In that case would I use V_s/V_p = N_s/N_p? Manipulate for V_s and then solve?

 

[kuruman]

So you mean to tell me that the primary transformer has 10 turns and the secondary has 1 turn? In that case would I use Vs/Vp = Ns/Np? Manipulate for Vs and then solve?

I mean to tell you that there are two transformers. Read the problem carefully

A pair of power transmission lines each have 0.68-Ω resistance and carry 650 Amp. If the primary voltage of the 10:1 step-up transformer is 4.6 kV, calculate the input voltage of the step-down transformer at the other end.

There is a 10:1 step up transformer at one end of the transmission line and a step down transformer at the other end connected to the load.

 

[ilovejava]

I mean to tell you that there are two transformers. Read the problem carefully

There is a 10:1 step up transformer at one end of the transmission line and a step down transformer at the other end connected to the load.

Okay, this is what I have come up with. The voltage is stepped up from the first transformer therefore, the current is stepped down. I calculate the secondary current by using I_s/I_p=N_p/N_s and I end up getting 65A. To find the input voltage in the second transformer I simply used V=IR noting that R = 2(.68), and I end up with an input voltage of 88.4 Volts

 

[kuruman]

... and I end up getting 65A.

Is this the current in the transmission lines? The problem states that the transmission lines carry 650 A. Consider finding how much power is lost in the course of transmission. Subtract that from the power going in and that is the power that reaches the step down transformer at the other end.