Physics Urgent Help please?

Question

Can someone please help me? "electric power"

16. What turns ratios would be required for transformers that change;

a) 20 000V to 500 000V (at the power station)

b) 500 000V to 11 000V (at a sub-station)

c) 11 000V to 240V (at a pole-type transformer)

this is what i have been trying to do, is it correct?

16a. 20 to 500
b. 500 to 11
c.

Answer 1

A. 20KV to 500 KV at power station divide 20KV into 500 kv to get the turns ratio needed
that is going to be: 1 :: 2.5 ratio. for every one turn in primary you will have 2.5 turns in secondary

B. 500KV to 11 KV the is going to be a step down transformer so you divid 500 KV by 11 KV which gives you a 45.45 or 45.5 :: 1 turns ratio for every 45.45 turns in the primary you will have 1 turn in the secondary.

C. 11KV to 240 VAC is going to require a step down transformer. so you divide 11 KV by 240 to get your turns ration there: 11 x 10^3 / 240 that is going to give you a turns ratio of: 45.83 :: 1

Ok you should notice two things right off one: is that they are non standard turns ratios as a rule. Two is if it is a step down transformer the more turns are the first numbers and if it is a step up transformer the larger of the two ratios will be the second number.

A. First is 1::2.5 you have fraction in which as a rule in most commerical transformers is not used:
So in that case it to make both numbers whole numbers simply multiply by two which gives you a ratio of:
2 :: 5

B. You again have a fraction or decimal number to make that it a whole number you simply double both sides so that becomes a ratio of:

90 :: 2 or the other way if to round down so that it becomes simply 45 :: 1 or 46 :: 1 ratios.

With the 90 to 2 ratio you are going to get 11.11KV out of your secondary.

With the 45 :: 1 ratio you are going to get 11.11 KV

With the 46 :: 1 ratio you are going to get 10.7 KV out:

This is where it gets interesting designing a power disturbation network:

C. You need as close to 240 as you can get without going below 240 votls correct:

Now we do some calculating to find the best ratios for the system using standard ratios (no decimals or fractions)

First thing you have a decimal in your ratio we need to get that to standard form no decimals. Which is 45.83 :: 1 right so the best in this case is to start out by rounding up which up give you 46 :: 1 turns ratio.

Now we check it out by plunging in some numbers and doing some calculating.

from power house good to go no problem since by doubling it we came out even.

At substation we came out with several numbers: Plug them in: We'll 11.11 KV first:

11.11 KV we need 240 VAC right so.

11.11 KV used C.'s ratios: 46 ::1 and that comes out to 241.53 volts. Only 1 1/2 volts high well with in tolerance:

Now make final design specis:

A: 2 :: 5 turns ratio step up transformer
B. 45 :: 1 turns ratio step down transformer
C. 46 :: 1 turns ration step down transformer

Hope that helps some! That is theory assuming perfect transformers. Numbers will be a little different when taking into account core and hystersis loses.

By the way if you was a company I'd be charging you for that.

Answer 2

We would normally factor down the ratio to the simplest ratio

a) 1:25
b) 500:11
c) 275:6

Or you could give them as a decimal fraction like in the answer you got the last time you asked this question.