How to generate 380/415 50hz

OK guys I've got an interesting one for you. We test every machine we build before shipping; for US shipments this isn't a problem, but for machines going over seas we test at the appropriate voltage (380-415 adjusted via voltage regulator) and frequency (50HZ) using a 25KW 50HZ generator (from who knows where) driven by a 20HP electric motor. Well this generator has been great since 1950 something (long before me), but lately (last 2-3 years) its been a maintenance nightmare.

I'm looking for a replacement, but am curious if I can just use a freq drive as a generator... A typical machine will have a 500VA control power transformer and 5HP water pump. The heaviest load is a machine with a 500VA transformer, 7.5HP water pump, 2HP fan, and 1/3HP oil pump.

So what do you guys think? Could I get away with a 15HP freq drive powered off of 480/60? Would it cause problems?

Should be fine. Just make sure your set to constant V/Hz ratio mode on the drive. (460 ÷ 60 = 7.66 and 7.66 x 50 = 383)

It can work, but you need to be careful with switching 'Across the Line' motors on and off while connected to a VFD. VFD's do NOT like motor loads operating independently, and will generally trip on instantaneous overcurrent.

I'd at least consult your drive suppliers, and have them certify your intended application.

You most certainly can use an inverter for a power supply. I have seen VFD's used as UPS inverters.

Most drives should have a standard V/HZ parameter you can preset. For testing most control panels a 5 or 10 HP drive should do just fine. It will allow you to power small inverters and run them sans motors.

You should consider a carrier stripper filter. It gives more sinusoidal waves. Some control transformers do not like the PWM output and could saturate.

rdrast,
That's my concern. I've got almost 10HP in three motors that will turn on and off (simple contactor) as the machine is tested and run.

I've had very little interaction with VFDs hence my concern/questions... I've always used VFDs to control a single motor and let the VFD spin the motor up...

If you do not have the motors loaded they draw small amounts of current. Your source would not need to be rated larger unless you do a full load to all motors during the test.

I suggest you figure out the total AMPS needed by the 3 motors and then get a VFD large enough to provide that current with at least 150% capability. Say you need 15 amps get an inverter rated 22 to 25 amps.

You can use any size HP/AMP rated VFD you want for this application. The carrier stripper on the output will make things smoother.

At my old company we use to struggle with this also:
generators from 50's, VFDs etc
until we found that the easiest way to rent Caterpilar portable generator.




You can get as big as 400Amp if I remember correctly.
Rental company brings it in, we test machine and they take it back.
Generator is gasoline powered and very easy to use.
We ran permanent cable outside and made hook up point at the closest parking spot.

v/hz

You would set the max hz to 50 and leave it there. Then if your motor voltage was 380 set the max volts to 380. If the motors were 415 set your max volts to 415. Then when you run your drive up to 50 hz you will have the right v/hz ratio. This will work, but you may run into trouble if all three motors are not turning the same direction. If they don`t all run the same way you may have to get a separate drive for each direction. On most drives you have to tell them it`s ok to reverse swapping the leads on the bottom of the starter will not change direction. This can cause gray hair. i know how your generator feels i`m a 48 model

This will work, but you may run into trouble if all three motors are not turning the same direction.

Click to expand...

What difference would that make if they do not drive the same device or material? What about 2 rollers being used to "pull" a material into the machine?

Another option to consider in the future is to use devices rated 50/60 hertz.

"On most drives you have to tell them it`s ok to reverse swapping the leads on the bottom of the starter will not change direction"

Changing the feed to a drive won't make any difference to rotation won't make any difference , but swapping them coming out will . Can't see what the problem is , the "generator " drive will simulate 3 phase at 50hz/380V , clockwise red-yellow-blue , you would set motor direction as you would with a "normal" supply.

Thanks for all the great feedback; I'm thinking this will work, but here's a couple of notes based on responses so far.

All the motors will be loaded. The machines in question are humid air generators (http://prodcd.samjackson.net/humidaire.htm) and during our testing we run them pretty hard. The motors get turned on and off via contactors via the PLC. There is a specific sequence that must be followed to get the machine to light so I can't have the motors ramp up with the VFD.

Motor rotation is one of the things we check in our testing; The pumps (oil & water) have to spin the right direction to get any output to speak of as does the fan.

I don't see why swapping the leads at each motor to ensure proper rotation wouldn't work on a VFD... I know that in the past when a VFD spun a motor the wrong way I'll I've done to correct is swap the leads somewhere after the VFD (before wouldn't change anything, right?).

I like the idea of setting the drive up in V/HZ and then setting 50HZ max and either 380 or 415 volts max depending on application.

How much over-sized does everyone think the drive needs to be to handle starting current for these motors?

Thanks again guys.

I suggest a minimum of 150% of the full load. If you full load is 30 hp then I would get at least a 45 to 50 hp drive.

Most drives can handle 150% current for a normal ramping motor but do not like the shock load effect of the across the line starting amp load. They could easily trip on overcurrent with out a goodly amount of cushion.