I have a customer that is wanting to convert some newer upgrades of a grain operation into 3 phase. Currently all that is available is a 400 amp single phase 120/240 service. Now in the past we have considered installing a 3 phase service but it has proven to be more costly considering this is a seasonal operation. Taking that into consideration, I believe that at this point, it is wiser to itstall a phase converter for the time being.

Can anyone give me some leads on some calculations to determine what I will need to install. I will be operating a 25HP, a 7.5HP and a 15HP, respectively at the same time. What I need to determine first is what the sigle phase load will be while these are running. There will be other single phase 240VAC loads running at the same time also but I am mainly concerned at what this new load will be.

Thanks
Kevin

In a word .... Don't.

Phase converters are outclassed by VFD's, or frequency drives. Single phase in, three phase out - and with added features like soft start and speed control.

Try going on the Arco Roto-Phase site. They are just one rotary converter manufacturer that came to mind.


http://www.arco-electric.com/SizingAssistance.cfm

The Roto-Phase is a motor/generator which creates a 3rd phase through it's rotation. They work quite well for years without problems, but that being said Reno is right, the VFD is a much better product especially if you are on any sort of demand charge billing. The price of VFD's is good and they are readily available. I would install the VFD.

That being said, I have many 20 plus year old Roto-Phase sites that just keep plugging along and they will not be replaced until something dies.

I recommend TVSS protection on either installation.

We had an extensive thread on this subject [Hill-billy saw miller [SP] /2003?] on various single to three phase options, including running big three-phase motors with a donkey motor etc, quite a few years back. If memory serves me right, aren't phase converters required to be rated at about double the expected demand?

Agree. Also, they are easy to size, by FLA, located on the nameplate. No moving parts and no maintenance other than a good vacuuming every so often. VFD's are much less money that a rotary converter, and easily installed and set up.

Try:
www.automationdirect.com
www.baldor.com
www.tecowestinghouse.com
www.wegelectric.com

Search the sites using keyword "AC Drives"

I understand that VFD's are easier and less expensive but in this situation, there will be 5 new 3 phase loads added. So, wouldn't I need 5 VFD's or not?

If they are all motour load and they are running the same time or not ? if not sometime it cheaper to get RPC instead of VSD's depending on motour size
But there is a major gothca almost all VSD are rated for one motour only so that something you have to think about it


Merci,Marc

5 VFD's or not? You ask as though that's a bad thing.

I bet you find that none of the three phase loads need to run at full speed - and that each has a different 'sweet spot.' In that instance, a drive for each unit is a real bonus. You also have enhanced reliability; one bad unit will not affect the other loads.

That do make sense there.,

sometime it work the best like that way.

Merci,Marc

Some things to be aware of with Variable Speed Drives.

1) The motors may need higher voltage rated insulation due to the harmonics present on the output of the VFD.

2) The distance between the VFD and the motor is usually limited to less than 100 feet.

3) Depending on the design of the VFD, you MAY need inductors either on the input to the VFD or between the VFD and the motor.

4) The motor may need to have insulated bearings installed to stop the induced current on the shaft from arcing thru the bearings to frame ground.

5) You MAY need special cabling between the VFD and the motor.

I am not trying to discourage you from using VFDs, I am just trying to make you aware of possible pitfalls.

Larry C

Your "keyword" is (may). Everything you mention is a possibility. He "may" need to address some of these possible issues. But he "may" not.
Good post. Everything you mention is possible.

You WILL need screened cable between the output of the VSD and the motor.

I've seen this time and again with RFI problems where the installing sparky just used Romex-type cable, do it once, do it properly.

We have a type of cable over here that is called Varolex, it is made specifically for VSD's, I'm not sure if it is available in the US, but using anything less is rather silly.

With regard to the list of things above, the problems with harmonics, bearing burn, etc, got ironed out a couple of years ago, there were a few VSD manufacturers that nearly got sent to the wall, after these things were picked up.

I mean, a factory that has a heap of these things installed, wants action NOW, not wait until the next best thing comes off the production line.
Thankfully, a lot of motors and VSD's were replaced under warranty ( some were out of it too).

But, if you get a brand-new VSD these days, I seriously doubt that (if installed to the manufacturers specs) you'd have any issues.

One caveat though, these devices are certainly not a plug and play thing, there is usually a pretty thick manual that comes with them, this should be read thoroughly (avoid the usual safety warnings garb at the front).

Most of the VSD faults I have ever been sent to have been caused by either the thing not being installed properly or it had not been set up appropriately for it's application (ie: the settings for start up or ramp-down were too slow or too fast).
Just bear in mind, at the end of the day, even with all that flash control system on the front end, you are still using a motor at the other end, VSD's cannot perform miracles.

I know the drive manufacturers and wire manufacturers are making a killing on these new output cables. I am sure they work very well. But, I have installed and repaired hundreds of VFD's in my career. THHN with line and load reactors always did the trick for me. You really do not need the load reactor unless the distance from the drive to the motor is very long. Like over 100'.
Never mix line and load conductors in the same raceway. Always run control logic cables separately in there own raceway. Always program the carrier frequency as low as possible. Buy quality drives. Price is not always the indicator.

In many parts of the world, it is a common practice to use cables (think SO cord) instead of 'pipe and wire'. For all but a very few instances grounded metallic conduit serves the same purpose as screened cable.

Yes, but it (the conduit) is more expensive.