Voltage tolerance limits for 550-V motors?
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  1. #1
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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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