transformer backfeeding

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mendownunder

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I was asked to reverse a 480v to 240v 3 phase stepdown transformer transformer to 240v to 480v stepup transformer. I do not have the particulars yet but was wondering how this is achieved and how the connections are made. Thanks....Dave
 
the transformer still gets hooked up the same it's just that you will need to check the conductor size on the 240 the transformer kva is the same so the conductor on the 480 size will be large for the kva.
 
bob cape may said:
the transformer still gets hooked up the same it's just that you will need to check the conductor size on the 240 the transformer kva is the same so the conductor on the 480 size will be large for the kva.
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If the cables are sized correctly for the transformer then the cable sizes should stay the same even if you feed the transformer from the opposite direction making it a step-up transformer. KVA is KVA so the current will be the same on both sides whether your stepping up or down
 
mendownunder said:
Tis simple as that? My 240v will connect to my H terminals and my 480v to my X terminals?
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no, your 480 still goes to H and your 240 still goes to X. think about what would happen if you put 480 into the low side, you would get 960 or something out of the high side
 
wireguru said:
no, your 480 still goes to H and your 240 still goes to X. think about what would happen if you put 480 into the low side, you would get 960 or something out of the high side
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BUT this is actually a Step Down transformer that I am trying to get 480v out of from 240v ... Dave
 
mendownunder said:
BUT this is actually a Step Down transformer that I am trying to get 480v out of from 240v ... Dave
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Wireguru is correct in connecting the 240 to X and the 480 will come from H, but be forewarned that if this is a Delta-delta connected transformer, you will not have 277 output. Only 480.
 
mendownunder said:
BUT this is actually a Step Down transformer that I am trying to get 480v out of from 240v ... Dave
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Won't make a difference...

Hi Voltage H = Low Voltage X
Low Voltage X = Hi Voltage H


If we change the letters to numbers...
480=240
240=480

...and then look at ratios:
1:2
2:1


HV X might look like this:
480=960

Hi Voltage X = $$$ and an explanation to the client about who released the holy ghost.


Of course the above is not technical jargon...here is that:
Voltage and Current: Primary (p) secondary (s)
Power(p) = power (s) or Ep x Ip = Es x Is
A. Ep = Es x Is
Ip
B. Ip = Es x Is
Ep

C. Is = Ep x Ip
Es

D. Es = Ep x Ip
Is

Voltage and Turns in Coil:
Voltage (p) x Turns (s) = Voltage (s) x Turns (p)
or Ep x Ts = Es x Ip
A. Ep = Es x Ip
Ts
B. Ts = Es x Tp
Ep
C. Tp = Ep x Ts
Es
D. Es = Ep x Ts
Tp

Amperes and Turns in Coil:
Amperes (p) x Turns (p) = Amperes (s) x Turns (s)
or Ip x Tp = Is x Ts​
A. Ip = Is x Ts
Tp
B. Tp = Is x Ts
Ip
C. Ts = Ip x Tp
Is
D. Is = Ip x Tp
Ts​

 
mendownunder said:
BUT this is actually a Step Down transformer that I am trying to get 480v out of from 240v ... Dave
Click to expand...
You can feed the transformer with 240V on the LV side and, off load, you'll get just about 480V on the HV side. On load, you won't.
By how much depends on transformer design.
 
Thanks To All Of You .... And Celtic For The Extra Effort To Remove This Mental Block From Me.... Now ... I Really Do Understand!!!! Thanks Again!! .... Dave
 
Besoeker said:
But it does make a difference.
The turns ratio isn't quite the same as the voltage ratio.
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You can't read the first 4 words of a post and stop :D

celtic said:
Won't make a difference...


Of course the above is not technical jargon...here is that:
Voltage and Current: Primary (p) secondary (s)
Power(p) = power (s) or Ep x Ip = Es x Is
A. Ep = Es x Is
Ip
B. Ip = Es x Is
Ep

C. Is = Ep x Ip
Es

D. Es = Ep x Ip
Is

Voltage and Turns in Coil:
Voltage (p) x Turns (s) = Voltage (s) x Turns (p)
or Ep x Ts = Es x Ip
A. Ep = Es x Ip
Ts
B. Ts = Es x Tp
Ep
C. Tp = Ep x Ts
Es
D. Es = Ep x Ts
Tp

Amperes and Turns in Coil:
Amperes (p) x Turns (p) = Amperes (s) x Turns (s)
or Ip x Tp = Is x Ts​
A. Ip = Is x Ts
Tp
B. Tp = Is x Ts
Ip
C. Ts = Ip x Tp
Is
D. Is = Ip x Tp
Ts​

Click to expand...
 
celtic said:
You can't read the first 4 words of a post and stop :D
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Sir, I read all of your post.
Including your equations.
It is based on turns ratio.
That isn't the whole story.
 
Besoeker said:
It is based on turns ratio.
That isn't the whole story.
Click to expand...
Here is a quote from a Siemens installation manual:

Transformer Turns Ratios

All transformers 3 kVa and larger are wound with exact turns ratios according to their voltage rating. This means that they can be used for either step up or step down applications. If a Delta-Wye transformer is wired in a reverse (Wye to Delta) application, then its neutral should not be connected.
Click to expand...
 
chris kennedy said:
Here is a quote from a Siemens installation manual:
Click to expand...
That's fair enough but the voltage won't be exactly the same as the turns ratio.
That's the only point I was making.
 
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