100HP with 230VAC 1

[jartgo]

I recently was looking at a project where I was being asked to replace a 100HP motor. Certainly one would assume that the motor is powered by 460VAC...not so, it's 230. There are three transformers hanging on the pole. I can't explain why the original project didn't include 480 transformers.

In working with the client on this project, I've suggested that they check with the power provider to see what it would take/cost to upgrade the transformers, then we could look at utilizing a separate smaller transformer for control voltages/etc. It's a small water plant and the three transformers on the pole serve nothing else.

It will likely not be worth it at this point to change the transformers due to all other power already being set up for 230...but is there an argument for running a motor that size on 460 vs. 230, that would be convincing enough to push the issue at this opportunity?

The cost/availability of the new VFD's for this size motor is troublesome as well, in the 230V rating.

 

[waross]

There are cost savings in the use of smaller conductors and conduits. If the money has been spent and this is a replacement motor there may not be enough energy saving to show a reasonable ROI on the cost of the changes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

A 100 hp 230 V motor is somewhat special - replacements would be more readily available with a 460 V motor, at least in the USA.

If a switch is made from 240 V to 480 V service, you may also lose the 120 V power (assuming 240 V wild-leg delta service), so you'd have to add a small stepdown transformer to come with the 120 V power that almost certainly is needed for something.

 

[automatic2]

it's dollars and cents. If it's exsisting, there's no further investment other than the replacement motor. Do your cost analysis as that's typically the motivator.

 

[jraef]

In my experience with this exact issue, it came down to the fact that it was a small utility service district and they did not have any other 480V users on the line, so all of the replacement transformers they had were 11kV-230V single phase. A big clue on that in your case is that they used three separate 230V transformers, meaning they must keep them around because most of their customers are single phase services. So from a utility practicality standpoint, it made sense for them at the time it was originally installed and the end user likely didn't care or wasn't given a choice. If their user base has changed, they may be more amenable to a 480V service now, it doesn't cost anything to ask.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[LionelHutz]

Instead of changing the service, why not just install a step-up transformer and a 480V VFD? It's a little backwards but could be a lot cheaper than changing the service and likely cheaper than buying a 230V VFD and motor.

 

[waross]

It is not clear if a new VFD is needed or if only the motor is to be changed.
A replacement motor may well be 230:460 Volt rated.
Service equipment: This will most likely need to be changed. I have installed 480 V or 600 V rated equipment (Most often breakers but switches also) for 208 Volt service because of availability but the odds are that you will have to change the service to 480 V or 600 V rated equipment.
Add the cost of a small dry type transformer and switches or breakers for 120:240 V lighting and control.
If a motor only is needed you don't have much incentive to change the voltage.
If a VFD is needed also the economics change.
If you are concerned with the possible future cost of replacing a VFD, it may be well to consider changing the voltage when and if the VFD must be replaced.
The I²R losses will be a little less at 480 Volts but not enough less to justify an equipment change except in extreme cases.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jartgo]

Sorry for the confusion. In fact the motors don't actually require replacing at this time, they were added in order to try to capture some efficiency with a premium eff. motor.

The VFD's are outdated and require replacement. The client wants a soft start bypass on the VFDs, and the availability along with pricing for these components in the 230V rated for 100HP are certainly the drive behind this exercise.

I appreciate all of the discussion.

 

[waross]

The client wants a soft start bypass on the VFDs,???

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Bill,
Pretty common really in some critical operations. If the VFD is off line for repair, their system is probably not stiff enough to start the motors Across-the-Line to keep them running.

Jartgo,
You shouldn't have too difficult of a time finding someone to quote you on a 100HP 230V VFD, but that's typically the limit. Rockwell makes them in their PowerFlex 700 Series (they pay me to say that) but if they make them, chances are most of the other major suppliers do too. I know for a fact that Yaskawa does, I've used them in the past. Looking around though, it appears that several of the European mfrs seem to stop at 75HP, maybe that's what you observed. That's probably because elsewhere in the world they would not likely ever use 230V for something that big. Here in North America though it's actually somewhat common in the HVAC industry. A lot of commercial buildings here don't use 480V, they have very large 208Y120V systems to avoid having numerous transformers on-site for all the office loads. So when they have a few large fan and pump motors, they just put up with using 230V.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Thanks Jeff.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter