Second set of eyes for 480 delta delta to 240/120

[Robert4709]

I'm stuck with a 480 3 phase 40 amp site line that I'm hooking up to some containers that have a a/c spec at 208-230V 15A. 2 amps of 120 lighting the occasional 20 amp 220 welder and some intermittent power tools so peak current is likely something around the 35a 220 and 20a 120 loss with nominal around 7A 220 only. I'd like someone to double check my asssumptions here and let me know if I'm missing something.

I'm considering a 20kva 3 phase delta primary to 120/240 delta secondary dry transformer with impedance around 5%. The Wye type being out of phase gave a 208 output which given losses over the length of the line would go below the spec of the a/c. Is this the correct transformer type and size for these needs and are there any considerations I should keep in mind to this specific type of setup other that the hot/wild line ?

 

[__dan]

I'm stuck with a 480 3 phase 40 amp site line that I'm hooking up to some containers that have a a/c spec at 208-230V 15A. 2 amps of 120 lighting the occasional 20 amp 220 welder and some intermittent power tools so peak current is likely something around the 35a 220 and 20a 120 loss with nominal around 7A 220 only. I'd like someone to double check my asssumptions here and let me know if I'm missing something.

I'm considering a 20kva 3 phase delta primary to 120/240 delta secondary dry transformer with impedance around 5%. The Wye type being out of phase gave a 208 output which given losses over the length of the line would go below the spec of the a/c. Is this the correct transformer type and size for these needs and are there any considerations I should keep in mind to this specific type of setup other that the hot/wild line ?

If you go delta secondary, only one phase will have a center tapped winding for 120/240 because the secondary is separately derived and there can be only one grounded conductor / system neutral. The other phase will be high leg, that's a red leg delta (you are proposing).

If you don't need 3 ph secondary, may as well save the cost and just go with a single phase 120/240 secondary transformer. The red leg delta 3 phase unit will have a lot of unused capacity and cost. If the A/C is 3 phase 240, red leg delta sounds like a solution. If the A/C is single phase, you have the choice of either single phase or three phase secondary.

One thing to check is the 480 Volt service or feeder supplied secondary may itself be a red leg (if delta) and have an available neutral that is 240 Volt to two of the legs. If that's there now. Possibly just cheaper and easier to go with one transformer and panel for the secondary instead of trying to tap load from a new 480 volt panel with single phase 240 in it. Good thing to check to look out for, to consider as an option the site may offer.

Total load, how many A/C's, if balancing the three phase load is necessary, is not clear

 

[Robert4709]

Currently hooked up is this transformer with neutral bonded to ground but I'm seeing an output of 277V across X1-X4 and 140V on X1-X2 with a input of 490V across H1-H2 I expected to see ~240 and ~120 why is this not the case? I ask because i feel if I hook up the new 1-phase transformer as it is a larger version of what is there I will see the same result but I need it to be 240 not 277

https://www.alliedelec.com/hammond-power-solutions-c1f003xes/70191814/

 

[Robert4709]

Correction voltage is reading 264v




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[GoldDigger]

Notice that the label seems to say that with the same primary tap jumpering the ouput from both 440 input and 480 input will be 240. That cannot happen. So what it is really telling you is that you can apply 440 at 50Hz or 60Hz but 480 only at 60Hz, and the output from 480 will simply be higher than the rated 120/240.
If an input of 440 gives you 240, then 480 should give you 261 and 490 should give you 267.

If you cannot accept that voltage you can either get a different transformer or get two small buck transformers to bring it back down again symmetrically.

 

[MAC702]

What would happen if you jumped 1-4 or 2-3, which should output between the 1-2 and 3-4 jumped values?

 

[Smart $]

What would happen if you jumped 1-4 or 2-3, which should output between the 1-2 and 3-4 jumped values?

The question is what is the current primary jumper connections? Looks like it comes 3-4 from the factory. Should be 1-2 for any voltage close to 480. If input varies from 480V, the output will vary proportionally. Possibly even exceed 120/240 output when input is exactly 480 and secondary is completely unloaded

 

[__dan]

Weird transformer. Label wiring diagram shows two identical single phase transformers, ie, are there two sets of identical H1 H2 line inputs or only one set. Likely only one set of H1 H2 so only one single phase transformer present. Two in the same can would be an odd dog but could allow an open delta connection.

You indicate 480 delta line is present. Is this 480 delta with four conductors or three, ie, is a neutral present, a line side equipment ground present, or is it three live lines with neither EGC or neutral conductor present, sometimes called three phase 480 with local "peg" earth grounding (if so very unsafe, as in lethal hazard present).

First verify there is an effective fault clearing path back to the source that is present as one line side conductor. If it's really remote privately owned site, that conductor can be load tested at 20 amp to see if it's there performance wise or they cheated or lost it somewhere in the implementation (seen that).

If the line side EGC is not present, reconnect one of the other line conductors as the EGC and then go with what you have left, 480 V single phase three conductors with an EGC (done that).

How many hot conductors remaining, two or three. If the load is not three phase, I don't see a benefit to going three phase on the secondary. If the containers are widely spaced more that 100 ft apart, you could carry the 480 to each container and drop individual 7.5 kVA single phase transformers at each. A/C would have to be off when the welder is running.

 

[GoldDigger]

The note in the bottom right corner of the label says it all:

"The primary voltage ratio of 240/480 is available only at 60Hz with a secondary voltage of approximitely [sic] 130/262." It is delivering exactly as promised.
BTW, the dots on the windings strongly suggests that the four windings are on a common core, so open delta is not an option. `

 

[Robert4709]

Weird transformer. Label wiring diagram shows two identical single phase transformers, ie, are there two sets of identical H1 H2 line inputs or only one set. Likely only one set of H1 H2 so only one single phase transformer present. Two in the same can would be an odd dog but could allow an open delta connection.

You indicate 480 delta line is present. Is this 480 delta with four conductors or three, ie, is a neutral present, a line side equipment ground present, or is it three live lines with neither EGC or neutral conductor present, sometimes called three phase 480 with local "peg" earth grounding (if so very unsafe, as in lethal hazard present).

First verify there is an effective fault clearing path back to the source that is present as one line side conductor. If it's really remote privately owned site, that conductor can be load tested at 20 amp to see if it's there performance wise or they cheated or lost it somewhere in the implementation (seen that).

If the line side EGC is not present, reconnect one of the other line conductors as the EGC and then go with what you have left, 480 V single phase three conductors with an EGC (done that).

How many hot conductors remaining, two or three. If the load is not three phase, I don't see a benefit to going three phase on the secondary. If the containers are widely spaced more that 100 ft apart, you could carry the 480 to each container and drop individual 7.5 kVA single phase transformers at each. A/C would have to be off when the welder is running.

To clarify the current transformer is not a delta delta I was looking to a delta delta for more load capacity as the current, above pictured transformer is just a small multitap single phate xfmr, one im planning to replace as it is both too small for my needs and not the correct voltage.

The question is what is the current primary jumper connections? Looks like it comes 3-4 from the factory. Should be 1-2 for any voltage close to 480. If input varies from 480V, the output will vary proportionally. Possibly even exceed 120/240 output when input is exactly 480 and secondary is completely unloaded

1-2 are presently connected on the high side.

The note in the bottom right corner of the label says it all:

"The primary voltage ratio of 240/480 is available only at 60Hz with a secondary voltage of approximitely [sic] 130/262." It is delivering exactly as promised.
BTW, the dots on the windings strongly suggests that the four windings are on a common core, so open delta is not an option. `

Gerr I just noticed that corner of the label myself shortly before reading this. I need 208-230 and and so I assumed (wrongly) some loss in the transformer to be below 240 and could use line resistance to take out another 10v without too much headache. I can't do that so easily with 24v drop requirement... so then the follow up is: is a 208y actually 208 or is it equally off and something around 220? I admit some frustration with seeing things that say 240/120 and aren't... So back to the drawing board.

Q1.How do I get the required 208-230 to the A/C ?

 

[MAC702]

...Q1. How do I get the required 208-230 to the A/C ?

Addressing this only.

I work with "208 - 230" HVAC equipment everyday, installing and repairing. These are nominal voltages to let you know that the same equipment is rated for both nominal 208 systems and nominal 230 systems.

Here, a nominal 230 system is an actual target of 240, with some specific sites measuring up to 243 at times.

Everything works fine.

 

[GoldDigger]

You use a buck transformer. A transformer with a 480 primary (that can tolerate 490 long term) and two isolated 24V secondaries can be put in series with the two output secondary ends to get roughly 110/220 center tapped and balanced. Or use two 12V secondaries instead to get very close to 120/240.
That additional transformer can be sized just to deliver the power associated with the voltage difference times the load current instead of the full load power.

Sent from my XT1585 using Tapatalk

 

[Robert4709]

First of all Thank you all for giving so much input in this, this thanks should have been at the top of my last reply but passed the 15 minute edit deadline fixing typos. I really do appreciate the time and experience your sharing here.

Addressing this only.

I work with "208 - 230" HVAC equipment everyday, installing and repairing. These are nominal voltages to let you know that the same equipment is rated for both nominal 208 systems and nominal 230 systems.

Here, a nominal 230 system is an actual target of 240, with some specific sites measuring up to 243 at times.

Everything works fine.

Im assuming though that the current ~263V is a bit too high

So currently my quandary is are all of the "240/120" delta type(if I got a 3 phase) and or single phase transformers like this where their secondary voltage actuals are 10% or so over and if so if I get a 208Y/120 instead of a delta delta will that be equally high by 10% and be a 225/130ish output. I havent bought the new transformer yet Im just trying to understand the system so I dont burn money on the transformer and end up burning out my electronics such as the A/C by being to far over/under but I admit I have no working understanding of the tolerances of all these things Im running mostly on a conceptual understanding from engineering classes years ago so pardon my ignorance in much of this.

 

[Smart $]

...
Q1.How do I get the required 208-230 to the A/C ?

Your interpretation of this [nameplate?] value is what perplexes me. A NEMA motor or motor compressor is [nominally] rated 230V when it is intended to be connected to a [nominal] 240V supply.

 

[Robert4709]

Your interpretation of this [nameplate?] value is what perplexes me. A NEMA motor or motor compressor is [nominally] rated 230V when it is intended to be connected to a [nominal] 240V supply.

Im not at the site atm I can get an image of it tomorrow to follow up.

 

[Robert4709]

You use a buck transformer. A transformer with a 480 primary (that can tolerate 490 long term) and two isolated 24V secondaries can be put in series with the two output secondary ends to get roughly 110/220 center tapped and balanced. Or use two 12V secondaries instead to get very close to 120/240.
That additional transformer can be sized just to deliver the power associated with the voltage difference times the load current instead of the full load power.

Sent from my XT1585 using Tapatalk

Im hoping just to select the appropriate single large transformer to replace this one to both increase my capacity and give the desired voltages I just was surprised at seeing the elevated voltage after his and am somewhat worried that if i go get a used transformer with incomplete documentation i may see a similar plate and wrongly assume it will be 120/240 out when its not.

 

[Smart $]

The note in the bottom right corner of the label says it all:

"The primary voltage ratio of 240/480 is available only at 60Hz with a secondary voltage of approximitely [sic] 130/262." It is delivering exactly as promised.
BTW, the dots on the windings strongly suggests that the four windings are on a common core, so open delta is not an option. `

Still a matter of loaded vs. unloaded voltage. A 3kVA transformer doesn't take much to load up... and there is actually a matter of voltage sag along with motor starting voltage. Now if you go back the the OP you'll find he is actually talking about a 20kVA transformer and using this one for comparison.

 

[Robert4709]

Still a matter of loaded vs. unloaded voltage. A 3kVA transformer doesn't take much to load up... and there is actually a matter of voltage sag along with motor starting voltage. Now if you go back the the OP you'll find he is actually talking about a 20kVA transformer and using this one for comparison.

I did do the voltage measurment with an 8 amp load on the 263V which gave me the 263V reading was connected with a 50ft 10 AWG line at the time which if it was 12 or 14 AGW would have had a more pronounced voltage drop. If the issue persisted in the next transormer one idea was to just use a 14 AWG for the 15A load and use the Line resistance to drop the V(though probably not the best solution) but you are absolutely correct that Im not trying to fix this 3kv into working im trying to learn from it in selecting the bigger one so I dont have to 'fix' the larger one.

 

[Smart $]

I did do the voltage measurment with an 8 amp load on the 263V which gave me the 263V reading was connected with a 50ft 10 AWG line at the time which if it was 12 or 14 AGW would have had a more pronounced voltage drop. If the issue persisted in the next transormer one idea was to just use a 14 AWG for the 15A load and use the Line resistance to drop the V(though probably not the best solution) but you are absolutely correct that Im not trying to fix this 3kv into working im trying to learn from it in selecting the bigger one so I dont have to 'fix' the larger one.

A 240V 8A load will not heavily load a 3kVA transformer to the point of voltage sag... so it is still performing as the note says. But the whole point for it even having a 130/262 actual output is to compensate for the nuances experienced when heavily loaded. Taking it to this level is not commonplace IMO.

Also, the disparity between a 230V motor voltage rating and a 240V nominal voltage supply isn't meant to be literal, i.e. forced. You do not have to use smaller gauge wire to ensure voltage drop. A 230V-rated motor will operate just fine on a nominal 240V system with minimal voltage drop. It'll just draw slightly less current when fully loaded.

I think you are overthinking the situation...

 

[Robert4709]

A 240V 8A load will not heavily load a 3kVA transformer to the point of voltage sag... so it is still performing as the note says. But the whole point for it even having a 130/262 actual output is to compensate for the nuances experienced when heavily loaded. Taking it to this level is not commonplace IMO.

Also, the disparity between a 230V motor voltage rating and a 240V nominal voltage supply isn't meant to be literal, i.e. forced. You do not have to use smaller gauge wire to ensure voltage drop. A 230V-rated motor will operate just fine on a nominal 240V system with minimal voltage drop. It'll just draw slightly less current when fully loaded.

I think you are overthinking the situation...

so if we scale the 3 kv to a 20 kv it is likely not to sag even given a 35A load so then I guess my question is is it ok to give the A/C 263V long term?