LV vs MV VFD 3

[JBUDA54]

Hello All,

I am on a project that has a 200HP Chipper Discharge Screw Conveyor that needs to be controlled from a VFD. I have research that the cutoff from LV to MV VFD HP is 500HP. ie below 500HP LV VFD and above 500HP MV VFD due to the economics. Most of these papers were written in the 90s. Are they any recent studies that have this type of data?

I have searched this site and goolged that info and can not find recent studies. I am trying to build a case that we need to use a 460V VFD vs a 2300V VFD. The cost of the motor and drive in the LV case will be cheaper but the cabling and installation cost will be more. With the price of copper going up I suspect that the 500HP cut off is changing to a lower HP rating.

But is 200HP a candidate for 2300V VFD control?

TIA Jbuda54

 

[jraef]

Not in my opinion. But it depends on a lot of other factors. If, for instance, you do not have enough capacity in your 480V system to add a 200HP load, then the cost of adding capacity must be weighed against the cost of just using the higher voltage. On the other had, if you do not have 2300V available already in the vicinity of the new machine, and you do have sufficient 480V, it would be a no-brainer.

The cost of a 2300V VFD is going to be extreme in comparison, partly because of the cost of the associated switchgear that goes with it, but also because at 2300V the VFD mfrs don't really make a 200HP drive. The smallest they make is probably 500HP, if even that small. They can LABEL it for 200HP, but you are really paying for whatever is the smallest power structure they can build. That used to be 2000HP at 4160V, so 1000HP at 2300V, but most likely it has come down since I last checked on anything that small.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

I don't think it would make economic sense, unless the 480 V system simply cannot handle the increased load.

You will pay a huge premium for a 2300 V drive compared to a 480 V drive for 200 hp.

 

[itsmoked]

And of course 2300V training...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Good point. I once started up some 4160V soft starters at a facility that had no other MV motor loads. The plant electrician had to take certification classes to be qualified to work on them, and when he finished, he hit them up for a hefty raise!


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ozmosis]

Unless there is already a motor on site rated 2.3kV then I would say it makes no sense at all. 200hp is more than adequate for LV applications.
I have a general idea that >1MW should be looked at with MV systems and below that LV (400-690Vac)is generally accepted as being a more cost effective for new installations. There are exceptions but this is a general idea.
Retrofit applications would be looked at differently.
Unless you are looking at km's of power cable then looking at the economics of copper versus the cost of MV drives/motors/switchgear/support/spares etc would push it LV imho.

 

[DickDV]

I like jraef's answer. Just for perspective, generally, if the motor leads are not long (say, less than 200ft), even a 1000hp LV drive/motor is probably the economic choice, both from an initial cost and from a maintenance standpoint.

Next week, I'm starting up a 1500hp 480V system on an extruder so even that can be justified under some conditions.

 

[LionelHutz]

Generally, there are a lot of factors involved in deciding on the voltage to use. System availability, cable costs, motor costs, VFD costs, electrician qualifications, etc

In this case, 200hp is very small for 2300VAC unless you don't have the lower voltage available.

I have seen a 10kV soft-starter installed for a motor that was something like 17A before which was likely pretty comparable cost wise to what you are asking.