Buck-boost xmfr questions

You're talking about 11 kW drives, and asking in sci.electronics.basics?

Get a real electrician before you kill yourself or burn your building down.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

You might try asking at rec.crafts.metalworking. (If you can wade through all the political dross.)

George H.

Greetings Phil, I wired my building and all the machines. It all passed inspection by WA state Labor and Industries inspectors. Puget Sound Energy said it was one of the best wiring jobs they had seen. The machine in question is running now but needs lower voltage to avoid a too high DC voltage in the VFD when the spindle decelerates. The power to my shop averages

245 volts which is about 5 volts higher than what the VFD wants. I just don't remember how to calculate for a buck xmfr since I only used one once years ago. But looking on line at the square D web site I see that the xmfrs I have are perfect for the job and are recommended by the Sqaure D buck xmfr calculator. I still need to determine if my phase converter is open delta. I think it is but need to be sure. But thanks for your concern. Eric

I'm relieved to hear that--you're the exception to the rule, then. If you look in the archives, you'll find a whole bunch of posters that seem to have had a death wish.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

** A 1.5kVA tranny with 25V secondary can deliver 60 amps continuous - this equates to over 14kVA in a 240 volt system.

You have three of them so the total VA available is 42kVA, so is far more than needed.

Get the wiring right - for Christ's sake.

.... Phil

You don't need a step down, you need a dynamic braking resistor to be attached to the drive or, you need to configure the drive's stop parameter to ramp to a stop and not coast to a stop. BUt if you're trying to stop it fast, you should do both the dynamic R and the ramp to stop set up.

The VFD should have terminals for the DB r and you must also turn on the function in the drive. Select the proper DB-R that fits your drive for maximum braking. Also, if the drive has vector mode in it, set it up for open loop vector, that'll keep things tight..

Jamie

Greetings Jamie, My first thought was braking resistors. Looking at the drive I could see no braking resistors or even the option for braking resistors. Reading the manual(always a good idea) for the Fuji Frenic 5000V2 drive reveals the reason: the drive uses regenerative braking. Braking resistors aren't even an option and I wish they were. I don't know more than the really basic about how VFDs work but the manual states that if the AC supply voltage is too high then upon deceleration the DC bus voltage can rise too high and cause the drive to turn off and set an alarm. The machine was previously connected, at the last shop it was in, to a Phase Perfect solid state phase converter (it is now connected to a rotary phase converter,AKA RPC). Overvoltage alarm and drive shutdown would also occur at the other shop but less often and at random times. It doesn't always occur in my shop with deceleration either. This random overvoltage problem is because the power at my shop and at the machine's previous location 6 miles from my shop averages 245 volts with spikes to 250 volts and above. This is a little higher than spec for the drive. The voltage from my RPC is well balanced and all the other CNC machines connected to it have no problems. These include three lathes with Fanuc controls, which are notoriously sensitive to unbalanced 3 phase, two machines with DC spindle drives, a mill with Centroid control, and a Fada milll. The Fadal mill came from the factory wired for and with the protection circuitry for 480 volts so I have a transformer connected between the RPC and the Fadal. And now it looks like buck wired xmfrs might be the solution for the Fuji drive. I hope so because I'm gonna try it. Eric

that's going to depend on the transformers. transformers in buck or boost mode need only be rated for the voltage difference times the current they handle.

not knowing what voltage you're trying to drop by 25 volts makes this question unanswerable.

if you can defined the line voltage you have, what you want it to be and the actual KVA required BY the VFD (not the load) , you can then figure out what you need.

Thanks for the reply. After getting all the info on the xmfrs I was able to find them on the Square D website along with the tables for choosing the correct xmfr. The ones in question are the proper ones to use. Now I only need to determine whether my phase converter is open delta or wye output. Eric

It will not run on single phase. In fact, it will set an alarm if any of the phases drops out. As far as loss of power goes, I already have several parts that run the spindle load meter to 120% for brief periods. 11 KW! It's cool to listen to the chips hitting the lathe enclosure. They sound like hail. Eric

Does that inverter allow you to operate single phase in? Many do and it is a simply way to make the DC bus a little on the weaker side. You'll get a reduction HP but you should still have enough.

Check the manual and see if you can run one leg missing coming in.

Jamie

And you verified that in the manual? Most of them you need to set a parameter to allow it to operate on single phase.. I can only assume you have looked at the manual for this and there is no option to set it up that way..

One of the drives we do this to uses a "Ignore Phase Loss" and it states that L3 is the phase you can drop out, internal control supply uses L1 and L2.

Jamie

Yes Jamie, I looked in the manual. This option was suggested in rcm. Apparently this drive is unusual in a machine of this size. From what other folks have said it is unusual for an 11KW VFD to use regenerative braking. I've been told that this type of braking is usually only used on much larger VFDs. Maybe that's why no single phase option. Or maybe it's because the drive is 27 years old. Eric