-Powering a 4KW laser with a generator ?

[zmm1]

Well its one mess onto the next. The owners have a plan to install a mazak space gear in a large offsite building in a rural area. The area has a REA electric system with their very expensive load demand fees. While the building has a 45KVA 208 service its nowhere near large enough.

The proposed plan is to install a 125 KVA onan generator on site to power the laser. I have suggested at a minimum running it through a isolation transformer, beyond that Im not sure. Im sure this is a strange configuration but I would appreciate any feedback the resident experts would care to share.

 

[krugtech]

I'm no electrical engineer but from what I've seen you need to consider what else you want to run off the generator. Dedicating the generator to the laser might not be the best idea. I would put anything in my shop with a constant loaded 3 ph motor like blowers or pumps that run constantly on the same generator. That stable load will help ballast the system. Put any surging dirty loads like motors that start under load on another generator. Go oversize on your wires and grounds if you can. Some equipment, like some compressors have options to run steady state, take advantage of this.

A well mapped system with careful consideration of the loads will run better than something thrown together and then patched with filters and transformers.

As for a transformer- a Y secondary with the center tap grounded seems to work best. This gives the lowest potential between phase and ground which keeps dielectric breakdown to a minimum. If your generator has a Y output, ground the center of the Y and consider using a transformer on the sensitive parts of the machine only. For example, I've found on some machines the frequency inverter for the blower is usually the only thing to go when the power gets a little dirty. Instead of putting an isolating transformer between the mains and the whole machine, I use a smaller transformer just on the inverter. This is not only cheaper but it also isolates the inverter from the machine itself as well as everything else. Some machine RF/HV sections make a little noise themselves and decoupling the inverter from this keeps it happy.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[ausman]

Hi ZMM1,

Some time ago we ran a 3Kw Rofin Slab of a large generator for around 3 weeks.
Machine didn't require a transformer so i can't hekp you there.

1 thing i can add is that it cost us around $500 per day in diesel, very exspensive.

also watch your voltage as it really goes up and down as the load comes on & off, the yaskawa invertor driving your roots blower might get a hard workout compensating the voltage changes.

I would not recommend doing it.
Besides after a few of months of chewing diesel you could probably have purchased a small HV sub station for the same amount.

 

[IRstuff]

What is your basis for selecting the 125 KVA generator? Electronic systems may have surge conditions exceeding 50% of specified power, so you should check with the manufacturer to determine what the actual peak surge power requirements are and plan accordingly.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[zmm1]

Thanks for replies gents, the gen choice was used as they al ready own it. It should work as the total demand is 91 KVA, vacume cooler res and motion control. That said I have also considered splitting the system up. Res on the generator and cooling and fans etc on the 208Y system..

As if that wasnt enough to cobb together, and maybe for the best. They now are considering putting in another REA system. A 480Volt 50 KVA system number 2. Again this is to duck under the load demand fees. In this configuration the res would run off the 480 50 kva utility line (system2) and the rest of the building (minor load) and cooler and vacume would run off the 208Y 50 kva system (system#1)

I know this sounds like alot of BS but the LDF's are very high, in our case 51KVA for 15minutes and 1 second equates to a 670 dollar surcharge. And yes even with a 100KVA system they still kick in at 51 KVA.

 

[krugtech]

Good luck man. Like IRstuff said startup surge can be a problem. You can delay start or soft start the system with some modification. For instance, start all the motors/transformers/whatever one at a time instead of all at once. Soft starting- starting motors on low speed windings then kicking over to the high speed windings or use an inverter.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[MacGyverS2000]

I'll just add... make sure any power going to control electronics is clean clean clean. Gen power isn't necessarily clean. Dirty power ruins electronics pretty darn fast, and you don't know what the problem is until it's too late.

Dan - Owner

http://www.Hi-TecDesigns.com