Transformer Taps

[infinity]

I have a transformer (480-208Y/120) that has a no load low output of 202/116 volts. What tap would you use to get the voltage closer to 208/120?

 

[LarryFine]

Try one step and measure again.

 

[synchro]

You're voltage is about 3% low, and the transformer has 2.5% steps. So like Larry said move one step, in your case one tap closer to each fixed terminal (H1, H2, or H3) on each winding of the delta. So move to the tap with the next higher number, which is labeled with a smaller primary voltage.
This gets you a 2.5% higher volts-per-turn on the primary, and therefore also a 2.5% higher volts-per-turn on the secondary. One step would give you 207V. Two steps would give you 212V.

 

[infinity]

You're voltage is about 3% low, and the transformer has 2.5% steps. So like Larry said move one step, in your case one tap closer to each fixed terminal (H1, H2, or H3) on each winding of the delta. So move to the tap with the next higher number, which is labeled with a smaller primary voltage.
This gets you a 2.5% higher volts-per-turn on the primary, and therefore also a 2.5% higher volts-per-turn on the secondary. One step would give you 207V. Two steps would give you 212V.

That was my thought as well, I would opt for using #5 and get an output a little higher than 208 volts. The issue is that there is equipment designed to run on 1Ø, 240 volts. Since our output is only 202 volts with no load they're blaming us for their equipment not working. I just want to change the taps to get it up to where they can no longer blame us if their stuff doesn't work.

 

[jim dungar]

Transformer taps can be confusing.
Typically they are set based on the primary voltage not being correct. So if your primary voltage is 504V (i.e. high), on this specific transformer you would connect to Tap #1 in order to have 120V out.

In your case, as synchro said, your voltage is about 3% low, so you need to use tap #4 or #5.

 

[LarryFine]

One step would give you 207V. Two steps would give you 212V.

I hadn't done the math. I would definitely opt for 212v with no load, if not higher.

I would also check it again under average loading, if changing it later is an option.

 

[GeorgeB]

The issue is that there is equipment designed to run on 1Ø, 240 volts. Since our output is only 202 volts with no load they're blaming us for their equipment not working. I just want to change the taps to get it up to where they can no longer blame us if their stuff doesn't work.

You aren't going to get there. If the equipment really NEEDS 240 (or 230), you'll either need a different transformer, or another step down unit or boost unit(s). Which is best depends on loads and costs.

 

[infinity]

You aren't going to get there. If the equipment really NEEDS 240 (or 230), you'll either need a different transformer, or another step down unit or boost unit(s). Which is best depends on loads and costs.

I agree, but until we provide them with the proper system voltage of 208 volts it's our problem because the vendor (who provided the incorrect voltage equipment) is blaming us. We're already submitting a proposal to install a transformer to get the voltage up to 240 volts.

 

[electrofelon]

Transformer taps can be confusing.

I agree. I always have to think about for several minutes, and still half the times I get it the opposite way I intended!

 

[jim dungar]

... half the times I get it the opposite way I intended!

I don't know if my batting average is even that high.

 

[LarryFine]

I agree. I always have to think about for several minutes, and still half the times I get it the opposite way I intended!

Think of it as that you're adjusting the voltage-to-turns ratio, not the voltage itself.

If you apply the same voltage to fewer primary turns, the output voltage must rise.

 

[Hv&Lv]

see if this helps. This assumes your true delta voltage is 480

 

[Hv&Lv]

if your at 116/202 now your delta voltage is at 466.


so put it on 466 tap it will go to 122. If for some reason it goes to 480, the secondary will go to 126.

 

[kwired]

Measure primary volts, connect taps according to primary volts and you should be close to 208/120 with secondary.