I think the reason why they want a grounded neutral is to keep the phase voltages controlled relative to a ground reference.
The drive chassis usually has several large ground lugs on it which are suppose to be tied to earth ground as would be the neutral. An ungrounded Delta power system can get out of control relative to earth ground. For instance, if for some reason one leg of a Delta goes to ground, the other two legs rise to a voltage equal to the line to line voltage away from ground. If you get an intermittent short between one Delta leg and ground, the voltages can swing all over the place relative to ground. That stresses any parts in the drive system which are referenced to frame ground. Back in the early 90's Siemens had one line of VFDs that had big problems blowing DC link capacitors. I was told that was because they were being used on ungrounded delta systems (used to be very common in industrial plants in the US) and if the Delta power source got out of wack, the capacitors would see high voltages to ground and explode. I saw a couple of them that literally blew apart the drive. That line of VFDs was short lived and they quickly changed their design. >> From the tone of the tech's voice he hears this problem a lot with 611 drive and rotary phase converters.<< The 611 drives are very popular. Many machine manufacturers used them for many years. Those guys have pretty much heard it all. Dave On 5/30/2012 3:19 PM, John Thornton wrote: > When we ran the generator we connected the 3 hots as usual and I don't > recall if we grounded it or not. I only had 3 connectors large enough > for the leads coming out of the generator so I'm sure we didn't connect > the ground to the neutral of the generator. > > http://cache.automation.siemens.com/dnl_iis/DA/DA0NDQzAAAA_59401543_HB/PJU_0212_en.pdf > > In that manual after a fault I have 4 status LED's lit up. On page 6-143 > the bottom 4 LED's are lit. Which one caused the fault I can't tell. > > The machine schematic does not show a neutral connected at the stepup > transformer and the infeed unit doesn't even have a neutral connection > and neither does the machine. > > From the tone of the tech's voice he hears this problem a lot with 611 > drive and rotary phase converters. > > John > > On 5/30/2012 1:12 PM, Jon Elson wrote: > >> John Thornton wrote: >> >>> I just got off the phone with Siemens tech support and "Our systems >>> don't run well on phase converters." >>> >> Well, given the way this system works, I'm not surprised by his comment. >> But, it is fairly close. You need to get into it and see WHICH trip it is >> getting. There probably are several different sensing circuits >> (over-voltage, >> under-voltage, lost phase, etc.) and knowing which one is the source of the >> trip should be VERY helpful. Right now you are flying blind, not >> knowing whether >> it needs more or less voltage, etc. >> >>> was the main theme of the >>> conversation as well as we can't run on a Delta system because we need >>> the ground reference I think he said. >>> >>> >> But, does the machine bring out the neutral? I think you said it does >> not, so >> his comment does not make sense. Well, given the way this system works, I'm >> not surprised by >> >>> Additionally he suggested a Delta to WYE step up transformer with >>> grounded secondaries between the RPC and the 611 >>> >> Well, if there's no neutral brought out, that doesn't make sense. If it >> is SUPPOSED >> to have the neutral connected, and the wire has been removed when it was >> supposed to be connected, then suddenly, a LOT of things start to make >> sense. >> >> If it needs a neutral connection, it may be possible to connect it to a >> balance >> transformer, which is three windings on one core, with all the wires at one >> end connected together as the neutral. >> >> When you used the Diesel generator, did you hook the neutral to something? >> You said you used the 208 V taps, was this generator a 120-208 Wye >> unit? If it worked fine on the Diesel with NO neutral connection, then >> this has no bearing on the problem. If you DID hook the neutral to >> something in the machine, then this may be the most important piece of >> data. >> >> Jon >> >> ------------------------------------------------------------------------------ >> Live Security Virtual Conference >> 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. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ >> _______________________________________________ >> Emc-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. 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