Maximum recommended motor hp served at 480v??

Status
Not open for further replies.
iceworm said:
Be nice to us uneducated sorts. What is a (are?) "polemics"?

ice
Click to expand...

A polemic (pron.: /pəˈlɛmɪk/) is a contentious argument that is intended to establish the truth of a specific belief and the falsity of the contrary belief. Polemics are mostly seen in arguments about very controversial topics.

The word is derived from the Greek πολεμικός (polemikos), meaning "warlike, hostile",[2][3] which comes from πόλεμος (polemos), "war".[4]
 
VFD app

VFD app

As the OP did state he would be utilizing a VFD the minimum sized transformer capacity requirement would typically be 500 kVA. If the application did allow for ACTL starts then a larger capacity would be required - but there are thousands of VFDs at 500 hp that are powered through 500 kVA isolation transformers. You could in fact purchase a PF7000 or PF750 with as integrated transformer (step-up, step-down, whatever you need) & Rockwells initial sizing for 500 hp would be around 500-600 kVA for that. If the existing 480 transformer and gear have capacity for at least 500 kVA I would have zero problems with adding a 500 hp motor on a VFD if that was a pump type application. If it were a high torque app that required 150% (or more) torque for long periods like a big conveyor then I would use a 600 to 750 KVA isolation (or capacity need on existing). If you have to add additional transfomer capactity for this application I would price out all the requirements to see if you go PF7000 or PF750, it may surprise you. I have done as high as 700 hp on a 480 volt Rockwell 1336 Impact & have also done some 400 HP 4 kV PF7000's & last month a 400 hp 480 volt PF755 at the same location. The last time I checked the break-over from a total cost stand point was around 750-800 hp. Above that point 4 kV was cheaper, but it will vary depending on current copper costs.
 
jcormack said:
As the OP did state he would be utilizing a VFD the minimum sized transformer capacity requirement would typically be 500 kVA. If the application did allow for ACTL starts then a larger capacity would be required - but there are thousands of VFDs at 500 hp that are powered through 500 kVA isolation transformers. You could in fact purchase a PF7000 or PF750 with as integrated transformer (step-up, step-down, whatever you need) & Rockwells initial sizing for 500 hp would be around 500-600 kVA for that. If the existing 480 transformer and gear have capacity for at least 500 kVA I would have zero problems with adding a 500 hp motor on a VFD if that was a pump type application. If it were a high torque app that required 150% (or more) torque for long periods like a big conveyor then I would use a 600 to 750 KVA isolation (or capacity need on existing). If you have to add additional transfomer capactity for this application I would price out all the requirements to see if you go PF7000 or PF750, it may surprise you. I have done as high as 700 hp on a 480 volt Rockwell 1336 Impact & have also done some 400 HP 4 kV PF7000's & last month a 400 hp 480 volt PF755 at the same location. The last time I checked the break-over from a total cost stand point was around 750-800 hp. Above that point 4 kV was cheaper, but it will vary depending on current copper costs.
Click to expand...

The cost of VFD may be equal or more than the cost of the motor itself. If cost consious, other options may be explored as is being done in previous posts.
 
Haji said:
The cost of VFD may be equal or more than the cost of the motor itself. If cost consious, other options may be explored as is being done in previous posts.
Click to expand...

What does this have to do with the question you were directly asked? I will ask it again.

WHERE IN THE NEC IS THERE A MINIMUM SIZING REQUIREMENT ON TRANSFORMERS?
 
weressl said:
Except it was you who made that statement and now you're diverting again and attribute it on somebody else. No integrity....
Click to expand...
I made the statement. No doubt in it. I also stated on what basis I made it. I also suggested to refer to the source for further details. There is no integrity issue here. Just a fault finding mentality involved here.....
 
Haji said:
I made the statement. No doubt in it. I also stated on what basis I made it. I also suggested to refer to the source for further details. There is no integrity issue here. Just a fault finding mentality involved here.....
Click to expand...

Are you claiming 'that' source stating that such limitation exist in the NEC? Since you have access to that source, please quote it - copy/paste - exactly as it appears.
 
80% rule for equipment capacity is not there in NEC. But NEC does recommend spare capacity and I think 80% rule for equipment capacity is based on it.
 
Sahib said:
80% rule for equipment capacity is not there in NEC. But NEC does recommend spare capacity and I think 80% rule for equipment capacity is based on it.
Click to expand...

where is this found in the NEC?

I did a search for 80% and did not find it used in this context anywhere in the code.
 
petersonra said:
in the NEC, there are no rules that require any spare capacity at all.
Click to expand...
Of course, the NEC has not so far made any spare capacity as a mandatory rule. However it has made it as a recommendation till date ( see its information note in post#51.).
 
Status
Not open for further replies.
Top