On 6/2/2012 12:41 PM, gene heskett wrote: > On Saturday, June 02, 2012 11:40:14 AM Dave did opine: > > >> On 6/1/2012 6:52 PM, gene heskett wrote: >> >>> On Friday, June 01, 2012 06:50:05 PM John Thornton did opine: >>> >>>> I posted on the C(ommerical)NCZone and a guy there says those drives >>>> are rated for a 3% inductance wye isolation transformer. >>>> >>>> John >>>> >>> BS alert there John. 3% of what? Without a frame of reference you may >>> as well be shopping for a good used car. >>> >>> Cheers, Gene >>> >> Gene, >> >> It is simply power system lingo.. here is an explanation that I believe >> is correct. >> >> http://www.control.com/thread/1026248874 >> >> > Which boils down to %Z = SQRT [ (%R)^2 + (%X x f/50)^2 ] > With the 50 being the frequency in HZ. > > With no 'where's to define the rest of it. This Phil Corso obviously has a > dog in this fight as nowhere in that thread is there a full, checkable by > anyone with a suitable set of measuring tools, explanation. Its all > "contact me off line". The clue about leakage reactance is valuable, but > still at the end of the day he has done little of educational value unless > you count the hand waving. > >
The only purpose I have used the % impedance for before is when I was doing short circuit studies on big auto plants so we could try and coordinate circuit breakers and make sure they were big enough to break a dead short.. We usually did not worry about a too high % impedance since the supply to the plant was extremely stiff. We were usually But in Johns case the lower the % impedance the better, but that directly translates into cost. Unfortunately if he buys a transformer it still might not work. That is why I would try and borrow one before opening my wallet for $1400. >> The higher the %, the more voltage drop through the >> transformer/reactor. So what John was saying is that the 611 system >> can use up to a 3% reactor, but no more. >> > Can I assume then that when the BBLB syndrome is accounted for, that a 3% > transformer is probably going to cost 50% more than the one yonder on the > shelf that sells for 1.4G's or less in the size John needs? > > >> Meaning the 611 >> expects a very stiff power supply, which really does not surprise me as >> it is a rather high performance drive system. Most of the machines >> equipped with 611s that I have seen are serious industrial machines >> where there is a 1000 amp 480 volt bus duct 50 feet from the machine, >> etc. >> > Well, at some point it should become a discussion where the cost of > switching the drives out for something that can tolerate a softer regulated > power supply source is becoming one possible solution. I expect that Johns > location, way off the main line, will account for the first 1.5% of that 3% > budget. Thats item 1. Item 2 is the cost, and the 24/7 power used to > power a ferroresonant regulator such as a Sola that big is a measurable > percentage of his monthly power bill. They run HOT, he could heat the shop > with it in cooler weather. But unlike the fans and/or AC, you can't turn > them off when you don't need the heat. They are also frequency sensitive, > enough so that driving it from the diesel generator is out unless it has a > .5% governor and double the size needed. > > Those drives in that size range obviously aren't cheap. IMO, I'd be > looking for parts to take his raw single phase, working into a full wave > bridge rectifier, with a serious choke to maintain the power factor to > something reasonable, and feed that into a switchmode regulator whose > output was the 600 volt DC bus the rest of it needs. With proper design it > is at least as efficient as the 60 HZ transformer, as its transformer is > ferrite cored and running at 30 kilohertz, and probably moreso, and could > hold that 600 volt buss at 600 with 0.01% regulation despite the startup > sags it would impose on the input line. And it shouldn't cost, if such a > beast is even available, any more than one of those 611 drives. > > The 611 infeed/power supply has a ribbon cable connection to the rest of the drive bus and it communicates with the other modules, so it is very much a smart drive system. If would be a major effort to make up a new infeed unit and create the control signals to keep the rest of the modules happy. The communications on the ribbon cable is proprietary. So the availability of such a beast might be the controlling factor. > One thing is for sure Dave, if I was 50 years younger and contemplating the > purchase of a machine that had these drives it it, I would certainly > discount my bid by the amount of headache this thread has become to John. > Bigger used 3 phase CNC machines oftentimes go for a lot less money than slightly smaller CNC machines that run of single phase and this is why. It has been a while, but I got the impression that John got that machine at a very good price. > But that is the advantage of hindsight. ;-) What we need to do now is > find a solution that Just Works(TM). The use of the limit2 module > functioning as a digital miller integrator to control the start up speed > ramp up, and the delta/wye isolation transformer, which will add its 3 or > 4% to the mix, might be the best solution for John. How that will fare if > a big inch face mill is installed remains to be determined. > > Cheers, Gene > ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
