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

  1. #1
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    Second set of eyes for 480 delta delta to 240/120

    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 ?

  2. #2
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    Quote Originally Posted by Robert4709 View Post
    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
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  3. #3
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    Currently hooked up is this transformer Name:  IMG_1698.JPG
Views: 120
Size:  133.3 KB 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-p...3xes/70191814/

  4. #4
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    Correction voltage is reading 264v




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  5. #5
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    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.

  6. #6
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    What would happen if you jumped 1-4 or 2-3, which should output between the 1-2 and 3-4 jumped values?

  7. #7
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    Quote Originally Posted by MAC702 View Post
    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
    I will have achieved my life's goal if I die with a smile on my face.

  8. #8
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    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.
    Lasciate ogne speranza, voi ch'intrate

  9. #9
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    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. `

  10. #10
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    Quote Originally Posted by __dan View Post
    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.


    Quote Originally Posted by Smart $ View Post
    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.

    Quote Originally Posted by GoldDigger View Post
    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 ?
    Last edited by Robert4709; 10-12-17 at 10:01 PM. Reason: I cant type aparently/clarity

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