Voltage tolerance limits for 550-V motors?
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    Default Voltage tolerance limits for 550-V motors?

    I have an Aciera F5 mill from the Canadian market. It is equipped with motors labeled 550 V on the nameplates. One motor is explicitly labeled as being wired Y, and I assume the other is, too. I have no idea whether the neutrals are accessible. In any event, what is the allowable range of voltages I can use to drive these things? +/-10%? This will help me pick a transformer. I have a commercial 240-V RPC that runs on the high side, perhaps at 245 V, on the non-generated legs. The mill came with a brand new 208-600V open-delta 3-phase autotransformer. I have not tested it, but the math says I should get over 700 V on the non-generated legs. Is this unacceptably high?

    (Sorry for the sideways and upside-down pictures. Blame my iPhone. (Which, by the way, is fantastic for reaching into dark obstructed places to visualize motor nameplates that would be silly difficult to see using a flashlight and mirror, and impossible otherwise, especially for my bifocal-ed eyes.)

    img_1480.jpgimg_1482.jpg

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    Quote Originally Posted by rklopp View Post
    a brand new 208-600V open-delta 3-phase autotransformer.
    Sure it is an 'autotransformer' (only..)?

    And may we have clear sight of the data plate on that critter? Cannot yet tell if a Prior Owner FUBAR'ed ....or got 'the right stuff'.

    Bill

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    Nothing is fubared. I witnessed the machine run on the seller's utility 208-V 3-phase running through the transformer. It is definitely an autotransformer, not an isolation transformer, and it is definitely open delta, because there are only two coils and cores. I don't have a pic of the transformer nameplate handy, but it is clearly labeled an open delta 10kVA autotransformer with only taps for 208:600. The transformer was the "right stuff" for his circumstances, but it may or may not be for mine.

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    Quote Originally Posted by rklopp View Post
    Nothing is fubared. I witnessed the machine run on the seller's utility 208-V 3-phase running through the transformer. It is definitely an autotransformer, not an isolation transformer, and it is definitely open delta, because there are only two coils and cores. I don't have a pic of the transformer nameplate handy, but it is clearly labeled an open delta 10kVA autotransformer with only taps for 208:600. The transformer was the "right stuff" for his circumstances, but it may or may not be for mine.
    Yah - I have 208 Wye here as one of many options. If I don't mind the cost of the Diesel fuel.


    Pretty sure it is NOT right @ 245 VAC 'actual' input and ~ 700 VAC out.

    OTOH, the Abene's loads are small as such things go, KVA-wise, so a more appropriate transformer altogether should be a wiser move than trying to diddle this one with add-ons.

    I go to NRI when I need Canadian-compatible gear. That might be a source for you.

    Bill

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    The mill is an Aciera and has a 1-hp feed motor and a 3-hp spindle motor. If I go by the rule of thumb to double the HP to get the kVA, then I need an 8 kVA transformer. Most choices seem to be 7.5 or 10 kVA. I suppose a 7.5 kVA transformer would work. The only time the feed motor delivers much power is during an upward (-Z) rapid traverse. That only lasts a couple of seconds typically.

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    Quote Originally Posted by rklopp View Post
    The mill is an Aciera and has a 1-hp feed motor and a 3-hp spindle motor. If I go by the rule of thumb to double the HP to get the kVA, then I need an 8 kVA transformer. Most choices seem to be 7.5 or 10 kVA. I suppose a 7.5 kVA transformer would work. The only time the feed motor delivers much power is during an upward (-Z) rapid traverse. That only lasts a couple of seconds typically.
    The 7.5 kVA will certainly 'work'. I even tracked an Eyetalian 6.6 kVA for a while for one of my needs. That, too would carry the Abene.

    A 10 kVA might be the better long-term choice - just in case you add sumthin' else - also perhaps easier to find at a decent cost.

    I have a 15 kVA, partly 'coz @ a mere $147 it was cheaper than several other options, and partly 'coz I was in the area (McKean, suburban Cleveland) off a long r/t by road to pick up five more Dee Cee motors from ERC anyway. Freight ELSE go-fetch is a major factor on these heavy boogers.

    So is 'inrush' at switch-on, BTW. Don't go TOO much overboard, lest code-mandated-to-nameplate feed wire, disconnects & breakers eat yer lunch.

    Bill

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    Are you saying you have a 208 transformer, but 245V available?

    Because that is getting to be too high for the transformer. It is almost `18% high, where 10% is the usual "good range" for electrical items, unless marked with a wider range.

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    Quote Originally Posted by JST View Post
    Are you saying you have a 208 transformer, but 245V available?
    The OP was yes.
    I actually have 208 Wye. If I need it badly enough.

    Because that is getting to be too high for the transformer. It is almost `18% high, where 10% is the usual "good range" for electrical items, unless marked with a wider range.
    700 VAC is more than 18% high for a 550 VAC nameplated motor's 'center' range. It is nearly 23% high against a 10% nominal allowance. More than double, IOW.

    Aciera motors may survive that, but they are NOT among the easiest to just go buy a drop-in replacement for, so I say JF go and get a more suitable transformer and move on to weightier matters. Like refurbing the REST of the machine and/or earning a crust with it.

    Bill

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    I finally got around to measuring the voltage with the autotransformer connected to my RPC. I get 715-V output for 245-V input. That's even a little higher than predicted by the nameplate ratio of 600:208. Time to look for an alternative transformer.

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    In general, I would look to get one with taps that will let you pretty much get it on the nose of the nominal voltage when you have your nominal voltage on the line. That way you will not be "using up" any of the allowable voltage range just with a mismatch.

    I'm surprised the autoformer behaved without complaint on your 245V. I'd have expected it to hum and growl a bit with that overvoltage. Looks like the ratio was almost perfect for 208:600, though, it figured out to a 607V output predicted, about 1% error.

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    Quote Originally Posted by JST View Post
    In general, I would look to get one with taps that will let you pretty much get it on the nose of the nominal voltage when you have your nominal voltage on the line. That way you will not be "using up" any of the allowable voltage range just with a mismatch.

    I'm surprised the autoformer behaved without complaint on your 245V. I'd have expected it to hum and growl a bit with that overvoltage. Looks like the ratio was almost perfect for 208:600, though, it figured out to a 607V output predicted, about 1% error.
    I traffic in 20 A Variacs for the test bench, but this rig needs "wire and forget" for reg'lar use.

    Waddya think of applying much more common & easily located buck/boosts to the input of that existing transformer while he scouts a 'less common' single transformer replacement?

    Bill

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    Quote Originally Posted by JST View Post
    In general, I would look to get one with taps that will let you pretty much get it on the nose of the nominal voltage when you have your nominal voltage on the line. That way you will not be "using up" any of the allowable voltage range just with a mismatch.

    I'm surprised the autoformer behaved without complaint on your 245V. I'd have expected it to hum and growl a bit with that overvoltage. Looks like the ratio was almost perfect for 208:600, though, it figured out to a 607V output predicted, about 1% error.
    It did actually growl a bit, but it seemed to occur more when the meter was across one of the three particular legs. Maybe I was imagining things. I did not stand there and poke the meter probes on the terminals. Instead, I opened the breaker and the disconnect, hard-wired the meter, and then closed the breaker and disconnect and read the meter. Those voltage levels scare me.

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    Quote Originally Posted by Monarchist View Post
    I traffic in 20 A Variacs for the test bench, but this rig needs "wire and forget" for reg'lar use.

    Waddya think of applying much more common & easily located buck/boosts to the input of that existing transformer while he scouts a 'less common' single transformer replacement?

    Bill
    Lot's of things are a workable make-do if you have to get going soon. That unit came with the machine, so..... Problem is it's wrong.

    Spend time finding a make-do is fine if you pull it out of the storage room. But it isn't as productive to actually BUY a "make-do", instead of getting what you need.

    It can't be that hard to find a straight-up solution. And he will have a unit to swap, if that is an option.

    Quote Originally Posted by rklopp View Post
    It did actually growl a bit, but it seemed to occur more when the meter was across one of the three particular legs. Maybe I was imagining things. I did not stand there and poke the meter probes on the terminals. Instead, I opened the breaker and the disconnect, hard-wired the meter, and then closed the breaker and disconnect and read the meter. Those voltage levels scare me.
    Good move.

    At those levels of power and voltage, the arc flash risk is getting into the "fry your face off" category, pretty much literally. Not like a 400A 480 line, but plenty bad enough as-is. I am firmly in the camp of " verify power off, attach probes with meter outside, close doors, check, shut off power". I do not have the PPE for that level, and do not want to fool with it.

    I've already been into the 450V plate supply in equipment enough to be pretty darn cautious. That blows pits in your skin... as long as the return path is not through your chest. DAMHIKT.

    In fact, there is a point to putting a properly rated fuse in series with the meter leads if they exit the enclosure.


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