transformer / rotary phase converter questions
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  1. #1
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    Default transformer / rotary phase converter questions

    Hi,

    I have gathered almost all the bits to power up my new to me CNC. Since last we spoke, I have ordered a 30HP rotary phase converter, and a 240 to 400V transformer.

    This machine was powered up in a shop that had 208 three phase, so as covered in a previous post, the transformer it came with would not suit my needs. However, the transformer was still wired up when t was delivered to me, and I was going to use the wiring from the old and transfer to the new transformer.

    I studied the configuration of the old transformer, and compared it to the wiring schematic on that machine. Yes, this is the old transformer I am asking a question about.... but I need to wrap my head around why that is different from the schematic, or just what I am overlooking here.

    My question first is about the connection at "X0".

    The secondary voltage clearly shows X0 is to be connected on the 400Y/231 side, but from the way this was wired, it was on the 208 side.

    In the picture I am going to attach to this post, coming in from the left has to be the 208 side, as the right side leads are marked "to machine".

    As far as I know, this machine was under power and the transformer did not look tampered with.

    I am resizing the pictures to post here right away, then I am going to be away from the computer the rest of today, so I will not be able to respond until tomorrow,

    thanks very much!

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    picture of 208-400Y/231 transformer showing connection at X0 from the 208 side.
    Attached Thumbnails Attached Thumbnails 208-trans-wiring-rs.jpg  

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    picture of schematic on 208 to 400Y/231 transformer
    Attached Thumbnails Attached Thumbnails 208-400y-transformer-schematic.jpg  

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    rb1, X0 is the center tap of the x1/x2/x3 secondary: it is often considered GROUND. You really need to tell us what servo motors and drives and what spindle motor and drive you have on this machine; I apologize if u told previously and I forgot: this is important. I can tell you that if it is fanuc stuff the x0 is not too important but if it is siemens then it is critical to be wired correctly.

    that said, since the x0 is probably not important or it would have been wired correctly (for siemens servos) it can be ignored or used, customer choice most of the time. your secondary 400v wye gives the 400v required for the machine and they obviously do not required the X0 or center of the wye tied to the machine. so some enterprising machine owner simply wired x0 to main shop ground most likely. doesnt hurt but not required most of the time.

    so to summarize, you should either ask the machine mfgr if x0 (center of secondary 400v wye) should be tied to the machine ground or not. If you cannot ask them that then tell us if it is a siemens drive system; if not, you can just ignore the x0 connection it should not be hooked up IMO.
    Last edited by mike_kilroy; 12-17-2010 at 05:19 PM. Reason: typo correction

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    thanks very much for that Mike, This machine uses FAGOR AUTOMATION servos...

    I just got home from picking up the Phase converter... so tomorrow I will have ALL KINDS of questions

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    siince it does not have siemens servos which require the x0, previous owner decided to ground the secondary. if it was my machine I would not do this but leave x0 unconnected. we often do not even bring the wye x0 connection out on xfmrs we have designed for our customers for just this reason; if not required they can wire it up wrong and screw stuff up. IMO hooking the x0 up to the primary/shop ground system defeated some of the purpose of the ISOLATION transformer - putting a shop ground reference on the otherwise ISOLATED secondary. If an intention is to ground the wye, why bother paying the extra price for an isolation transformer? this same transformer as an autotransformer, which does not isolate pri from secondary, would have cost nearly 1/2 the price.

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    Hi Mike,

    I see what you are saying... This machine was purchased from a local dealer who has them built in TW and the have all the Fagor Automation parts on them... but saying that, I am not sure if perhaps Fagor uses Siemens Servos... maybe I should take a way cover back off and check that. The electronics in the rear of the machine are all FAGOR branded drives.

    The local dealer did the complete original install, so perhaps they want the X0 hooked up. When I talked to them about needing another transformer (for my 240 service) they did not say anything about using an autotransfomer, they just told me to get the same one (size and brand), but with a 240 input rating. They may not know the workings of it as you do.

    I am attaching the schematic on my new transformer, I notice the input is now on the X1 / X2 / X3... just labeled different, or some other unimportant difference?

    thanks again!
    Attached Thumbnails Attached Thumbnails 240-400-transformer.jpg  

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    wow. double wow. whew.

    Beaver had Rex transformer Company in Canada (the brand we sell!) private label this transformer for them. I am surprised Rex would label it this way for them since it is wrong according to industry standards. Standard is primary is labeled H1/H2/H3 and secondary is labeled X1/X2/X3 (&X0 if brought out to a terminal). wow. Would you mind if I send a picture of this to engineers at Rex and ask them if it is a typo or something or why would they label it this way?

    You probably should not worry about it and use it as labeled since it also is not common to make a wye pri -> delta sec so it will no doubt work as labeled. Good catch on the wierd nomenclature!

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    Mike - sure send the picture over to REX, They made both transformers. (the one that was used on this machine in its previous life, and the new one I just bought.)

    I did not get as much done over the weekend as I wanted.... I need to get things fired up in the next few days. While reading over the instructions included with the RPC, I see I may need some sort of shut off between the RPC and the transformer... I take it that just leave the main power off to the CNC machine is not enough?

    Instructions seem pretty clear :" all loads INCLUDING TRANSFORMERS must be disconnected before starting the phase converter each time..."

    I guess I need to get a 3 phase disconnect switch before power up.

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    Here is a pic of the inside on the 240 to 400 volt transformer that I will be using.
    Attached Thumbnails Attached Thumbnails 240-400-transformer-inside.jpg  

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    And the servos are Fagor branded, or perhaps re-branded Siemens? anyone?

    Regarding the X0 connection (or rather H0 connection on the new transformer) to the input side... Since this was an operating unit, I would be inclined to keep that connected, or would you talk me out of that?

    thanks again all
    Attached Thumbnails Attached Thumbnails fagor-servo-tag.jpg  

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    OK, got the rotary phase converter powered up and tested the legs as per the American Rotary manual. All voltages are inline with what they require, so I am going to get the three phase disconnect wired up today and test the output of the transformer.

    I don't have any instructions with the transformer, so can someone run down what the voltmeter should read from the different taps?

    thanks alot!

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    Hey there, got the transformer powered up and turned the machine on this morning... so far so good! Have not made any chips yet, but cut some AIR today

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    Quote Originally Posted by rb1 View Post
    Mike - sure send the picture over to REX, They made both transformers. (the one that was used on this machine in its previous life, and the new one I just bought.)
    Hey rb1,

    I finally got a reply from Rex, your transformer mfgr about labeling their primary X1,etc and secondary H1 etc - very interesting history lesson!
    ========================

    from Rex:
    Interesting dilemma. Dave recalls that there once was a convention to label transformers with H1, H2 etc being the highest voltage regardless of whether the turns ratio was step-up or step-down. Then the utilities began to transmit at pretty high voltages and virtually all transformers became step-down and so the primary became H1, H2 etc by defacto. I also sort of remember RETMA "assuming" that electronics transformers were mostly stepping down "110V" to 12 or 24V for filaments et al and those transformers also had H1, H2 as the primaries.

    I don't think there is an actual standard.

    Dave
    ------------------------

    From: Mike Kilroy
    Sent: Monday, January 03, 2011 2:00 PM
    Subject: Re: FW: mslabeled rex xfmr?

    it was just a question about why they would make a primary X and sec H - thought that was totally against Osha, Fema, FTA, ETA, RMS, CE, UL, and Obamaski rules..... if not against regulations then ok; I just wanted to tell my buddy it was not a typo and not against rules.
    ----------------------

    On 1/3/2011 1:15 PM, Dave wrote:
    > What to do??
    >
    > From: Bob
    > Sent: Monday, January 03, 2011 1:10 PM
    > Subject: Re: mslabeled rex xfmr?
    >
    > Dave,
    >
    > Does your customer want a new name plate for the BA30C-N1/Z/B?
    >
    > The BA30C-N1/Z/B was built for Beaver Electrical Machinery in Canada and this is how they want the transformers labeled.
    >
    > Please advise.
    >
    > Thank you,
    >
    > National Sales Manager

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    Quote Originally Posted by mike_kilroy View Post
    rb1, X0 is the center tap of the x1/x2/x3 secondary: it is often considered GROUND. You really need to tell us what servo motors and drives and what spindle motor and drive you have on this machine; I apologize if u told previously and I forgot: this is important. I can tell you that if it is fanuc stuff the x0 is not too important but if it is siemens then it is critical to be wired correctly.
    Sorry to bring this up from the ancient caverns of practical machinist...

    This comment is very important. If you ever buy a CNC with a Siemens drive system... you need to pay attention:

    If you have a phase perfect phase converter and you are thinking of stepping up to the necessary 400V for the Siemens and you have an autotransformer handy that should be able to handle it, it will not work. The Neutral to Phase voltages must be balanced. Not on Fanuc, but on Siemens. Phase perfects do not have balanced Phase to Neutral voltages so when it passes through the autotransformer the problem will still exist.

    I just learned this at the worst possible time and I felt this nugget of important knowledge would have come in handy.

    I hope this helps someone out there.

    Dave @ Nerv

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    Quote Originally Posted by Nerv View Post
    Phase perfects do not have balanced Phase to Neutral voltages so when it passes through the autotransformer the problem will still exist.

    I just learned this at the worst possible time and I felt this nugget of important knowledge would have come in handy.
    Correct, the PP doesn't deliver a neutral. a 1:1 wye or delta transformer can be reconnected as zigzag (if you can get all 12 leads off the transformer) if you need to get a neutral after a transformer handles the 230 to 400v transformation.


    Someone correct me if i'm wrong but i think you can get a neutral point (no you can't ground it!) with a 69V:138V auto transformer connected from the generated third phase of the phase perfect to the neutral of your 120/240 incoming feed. two 24 volt 120/240 buck/boost transformers and a 32v transformer can have their 24 and 32 volt secondaries connected in series and their 240v primaries connected in parallel to get the ratio you need to do this. but it would be much more efficient to have a single tapped winding on one core.


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