Well I'll be a monkeys uncle, the step up transformer does have a N lug 
but nothing is connected to it.

Voltages at the drive input are
UV 525
UW 512
VW 508
Ug 225
Vg 225
Wg 370

John

On 5/29/2012 6:44 AM, gene heskett wrote:
> On Tuesday, May 29, 2012 07:33:26 AM John Thornton did opine:
>
>> While laying on the floor to change taps yesterday on the step up
>> transformer I noticed it says INPUT WYE. The transformer has 3 sets of 3
>> lugs for input 208, 220, 240. The only other wires on the transformer
>> are 3 lugs for 390v to the infeed unit and 3 lugs at 480v for the
>> cooling pump. The step up transformer frame is grounded to the same
>> place as everything else in the machine.
>>
>> John
>>
> You said "INPUT WYE", but made no mention of a center N connection.  How
> can it be a WYE if there is not a neutral?  Perhaps I'm still a pint low on
> coffee?
>
> More to the point, what voltage do you actually measure, to ground, from
> those 390 volt points?
>
>> On 5/28/2012 8:34 PM, Dave wrote:
>>> Yes, many/most big servo drive systems that I have worked on use a
>>> Delta primary - Wye secondary with a grounded neutral.
>>>
>>> I think the grounded neutral on the Wye keeps the voltage in check on
>>> the drive capacitors from a line to ground standpoint.
>>>
>>> I've purchased this type of  transformer for a couple of different
>>> servo projects.  They tend to start at about 10 KVA and cost about
>>> $1200 at that size.
>>>
>>> I think I have a 6 KVA unit in my shop.  Hmm... come to think of it, I
>>> have used that transformer to power Siemens VFDs and Parker servo
>>> drives off of my rotary phase converter without any problems.
>>>
>>> If you were closer, I'd loan it to you.
>>>
>>> Delta primary, Wye secondary transformers are pretty common around
>>> here.   But many are sold  specifically as drive isolation
>>> transformers.
>>>
>>> You have a step up transformer in your machine right now though, prior
>>> to your Siemens 611U power input module (fancy DC power supply);   How
>>> is that wired?
>>>
>>> Dave
>>>
>>> On 5/28/2012 8:05 AM, John Thornton wrote:
>>>> Gene,
>>>>
>>>> The phaseperfect install guide did mention that when you need
>>>> balanced voltage to ground to use a delta wye transformer after
>>>> their device. So I have to assume they are out there but so far my
>>>> google only turns up descriptions of the beast.
>>>>
>>>> John
>>>>
>>>> On 5/27/2012 4:09 PM, gene heskett wrote:
>>>>> Now, here John, is another thought if my train of thought follows
>>>>> and this thing is hooked up delta on the outside, but is 3
>>>>> individual loads to ground inside the kit, and which I can see
>>>>> objecting to the over voltages the phase converter generates,you
>>>>> might be very pleased with how it works IF you interpose a 3 phase
>>>>> transformer between your phase converter output and the supply to
>>>>> this kit.  Hook the input side up as a delta load, ignoring the
>>>>> center of the wye this idler motor has AND the center of the
>>>>> primary side wye (other than making sure, if it has individual
>>>>> bolts per phase, that they are connected together).
>>>>>
>>>>> Then ground to the machines neutral and effectively to ground, the
>>>>> center of the wye of this 3 phase 1/1 transformers secondary, and
>>>>> feed your kit with the outside 3 corners of the wye.  That should
>>>>> go a long ways to restore the "to ground" voltage balances.  The
>>>>> transformer will of course need to be rated at about 125% of the
>>>>> kits actual load.  And not having researched it, I'd have no clue
>>>>> as to the ready availability of such a beast.
>>>>>
>>>>> Doing a google search, I came across this:
>>>>>
>>>>> <http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm>
>>>>>
>>>>> which might make it a bit clearer than my word pictures.
>>>>>
>>>>> Cheers, Gene.
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>> Exclusive live event will cover all the ways today's security and
>> threat landscape has changed and how IT managers can respond.
>> Discussions will include endpoint security, mobile security and the
>> latest in malware threats.
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>
> Cheers, Gene

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