Picking apart a transformer.....

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Andy1845c

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Hello all,

Been lurking for a while and finally decided to jump in with a question.

I have two of these transformers to install. I haven't installed many before and decided it would be interesting to pick apart the nameplate.

The application is stepping down 480 to 240 for a piece of industrial equipment. Nothing weird. Mostly just hypothetical questions here.

http://imgur.com/uoRbEf8

Question 1. Can someone explain the drawing at the bottom of the nameplate - it appears the only difference is in one X2 and X3 are connected together and the other X4 and X2 / X3 and X1 are connected.

Question 2. I don't need 120v for what I am using it for, but I assume it could be used for 120v if I wanted to? Center tap being X2/X3?


Question 3. What are the various taps for? I assume there number are for input voltage? What are some situations where I would use something like 432v or 216? What is the 240 volt tap set up for? This one is confusing me.




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Andy1845c said:
Hello all,

Been lurking for a while and finally decided to jump in with a question.

I have two of these transformers to install. I haven't installed many before and decided it would be interesting to pick apart the nameplate.

The application is stepping down 480 to 240 for a piece of industrial equipment. Nothing weird. Mostly just hypothetical questions here.

http://imgur.com/uoRbEf8

Question 1. Can someone explain the drawing at the bottom of the nameplate - it appears the only difference is in one X2 and X3 are connected together and the other X4 and X2 / X3 and X1 are connected.

Question 2. I don't need 120v for what I am using it for, but I assume it could be used for 120v if I wanted to? Center tap being X2/X3?


Question 3. What are the various taps for? I assume there number are for input voltage? What are some situations where I would use something like 432v or 216? What is the 240 volt tap set up for? This one is confusing me.
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Click to expand...

Welcome

A1: The first drawing shows the coils in parallel, the second in series
A2: Correct
A3: The HV taps are used to compensate for incoming voltage. If the have 480V coming in, then tap #3-4 is what you'd use to get an even 240V on the secondary side. If your voltage is higher, you'd use taps 1-2 or 2-3; if it is lower, you'd go 4-5, 5-6, 6-7, or 7-8.

It would be extremely uncommon for incoming voltage of a 480V power supply to be at 432V (-10% nominal) to need to use those taps. There are numerous reasons why one might use those for other purposes but are kinda outside the scope of your questions.

The 240V taps require 2 jumps for parallel operation. If incoming voltage is at or close to 240V, you'd put jumpers from H1-H4 AND H2-H3
 
JFletcher said:
A1: The first drawing shows the coils in parallel, the second in series
Click to expand...

I'm not a transformer expert but I believe that the coils in series yield 240V with a center tapped 120v. While the coils in parallel yield only 120v but at twice the available amperage as the series coils. Correct?
 
Coppersmith said:
I'm not a transformer expert but I believe that the coils in series yield 240V with a center tapped 120v. While the coils in parallel yield only 120v but at twice the available amperage as the series coils. Correct?
Click to expand...
Total VA capacity stays the same, so if you halve the voltage you will double the current.
 
Coppersmith said:
I'm not a transformer expert but I believe that the coils in series yield 240V with a center tapped 120v. While the coils in parallel yield only 120v but at twice the available amperage as the series coils. Correct?
Click to expand...
Yes, that is exactly correct, but it needs to be worded differently in line with what kwired said. If you connect them in parallel, you get a single 120V circuit at the full VA capacity. With the center tapped version you could have one 240V circuit at the full VA capacity and/or two separate 120V circuits, each with 1/2 the VA capacity of the transformer. But at no time can any connection or combination of connections result in a load connection greater than the VA capacity of the transformer. I know it seems obvious, but believe me, there are a LOT of people who miss that concept and overload the transformer when using it to supply both 120 and 240V loads. It takes some careful (albeit not difficult) math on determining the loading.
 
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Jraef said:
Yes, that is exactly correct, but it needs to be worded differently in line with what kwired said. If you connect them in parallel, you get a single 120V circuit at the full VA capacity. With the center tapped version you could have one 240V circuit at the full VA capacity and/or two separate 120V circuits, each with 1/2 the VA capacity of the transformer. But at no time can any connection or combination of connections result in a load connection greater than the VA capacity of the transformer. I know it seems obvious, but believe me, there are a LOT of people who miss that concept and overload the transformer when using it to supply both 120 and 240V loads. It takes some careful (albeit not difficult) math on determining the loading.
Click to expand...

So if you used the series arrangement and had no 240v loads, you would get exactly the same amount of VA of 120V as the parallel, correct? Doesn't sound like there is an advantage to the parallel arrangement unless you are powering a single 120v power hog.
 
Coppersmith said:
So if you used the series arrangement and had no 240v loads, you would get exactly the same amount of VA of 120V as the parallel, correct? Doesn't sound like there is an advantage to the parallel arrangement unless you are powering a single 120v power hog.
Click to expand...
Pretty much so. Only other thing may be to avoid any possible poor neutral on a 120/240 system causing voltage instability.

Dual voltage motors are nearly the same thing - two windings placed in series for the high voltage or in parallel for the low voltage, either way the individual winding sees same voltage and current, if driven load is the same.
 
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