Dual Voltage Generator KVA & Amperage question - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Forum > General Electrical Discussion


Like Tree6Likes
  • 1 Post By B-Nabs
  • 1 Post By micromind
  • 1 Post By robg3987
  • 1 Post By Bird dog
  • 2 Post By Bird dog
Reply
 
Thread Tools Display Modes
Old 03-26-2019, 07:07 PM   #1
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default Dual Voltage Generator KVA & Amperage question

Hello,
I have a 480V/240V 125Kva 3 phase generator that I have a question about the available Kva's and subsequent amperage available at the 2 available voltages.
The stator windings consist of 6 sets ( 12 leads) connected in a series Y configuration. So 2 windings in series for A phase, 2 for B, 2 for C.

Each phase has a connection available mid point for the 240 V selection.

The generator is rated at 125 Kva @ 480V.

I am trying to verify the available max Kva and amperage for each voltage (480 & 240) .
By my calculations, @ 480V, I should have approx 150A.


However (this is where I might be unclear) at the 240V (mid point of the 2 series windings),, I should still be getting 150A through the winds (as they are in series, but now only 240 V, so now therefore don't I have only 62.5 Kva ( 150 A @ 240V) ???


Its not what I observed when I load bank tested it.
robg3987 is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 03-26-2019, 07:34 PM   #2
Senior Member
 
Bird dog's Avatar
 
Join Date: Oct 2015
Location: South East US
Posts: 4,963
Rewards Points: 1,700
Default

What does the nameplate say?
__________________
Popcorn munching forum observer
"The supreme art of war is to subdue the enemy without fighting." Sun Tzu
Bird dog is online now   Reply With Quote
Old 03-26-2019, 07:47 PM   #3
Watt Pusher
 
B-Nabs's Avatar
 
Join Date: Jun 2014
Location: Port Coquitlam, Canada
Posts: 2,163
Rewards Points: 466
Default

Wouldn't you parallel the windings for 240V operation? So you'd still have 150A per winding, but that would result in 300A per phase, so still the same KVA.

Sent from my SM-G920W8 using Tapatalk
splatz likes this.
__________________
Is that a real poncho or is that a Sears poncho?
B-Nabs is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 03-26-2019, 08:22 PM   #4
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default

Quote:
Originally Posted by Bird dog View Post
What does the nameplate say?
exactly what I posted ( 125 Kva at 480 Volts)
robg3987 is offline   Reply With Quote
Old 03-26-2019, 08:32 PM   #5
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default

Quote:
Originally Posted by B-Nabs View Post
Wouldn't you parallel the windings for 240V operation? So you'd still have 150A per winding, but that would result in 300A per phase, so still the same KVA.

Sent from my SM-G920W8 using Tapatalk
yes,, that is what I had expected to do, but we were told by the supplier that it would achieve the same KVa output in that configuration (non-parralled configuration).



I was wondering if I had something wrong in my theoretical predictions.
The other possibility is that the supplier is full of BS and running it like that will ultimately lead to burning out the winding.


I'm just making sure I haven't misunderstood the theory and my calculations
robg3987 is offline   Reply With Quote
Old 03-27-2019, 12:09 AM   #6
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,528
Rewards Points: 2,666
Default

Winding heat is dependent on amps; no part of any winding can be loaded beyond its amp rating.

KVA is amps and volts.

In your case, if you get power from the 240 point only, the gen becomes 62.5 KVA.

You are correct in that each winding can produce 150 amps, at 480 this will be 125 KVA. At 240, it'll be 62.5 KVA.

You can also use any combination of 240 and 480 loads provided no part of any winding produces more than 150 amps.

Be careful with the 240 here, it's not 120/240, it's 138/240 because it's connected Y.
splatz likes this.
micromind is online now   Reply With Quote
Old 03-27-2019, 05:45 AM   #7
Hackenschmidt
 
splatz's Avatar
 
Join Date: May 2015
Location: Parts Unknown
Posts: 8,320
Rewards Points: 4,030
Default

Quote:
Originally Posted by B-Nabs View Post
Wouldn't you parallel the windings for 240V operation? So you'd still have 150A per winding, but that would result in 300A per phase, so still the same KVA.
If that's the case I'd picture something like this in the connections (in the low voltage configuration, would 1 be bonded to 4-5-6?)

https://www.electrical-contractor.net/theory/3ym04.gif
Attached Thumbnails
Dual Voltage Generator KVA & Amperage question-3ym04.gif  

__________________
Everything Should Be Made as Simple as Possible, But Not Simpler

Last edited by splatz; 03-27-2019 at 05:51 AM.
splatz is offline   Reply With Quote
The Following User Says Thank You to splatz For This Useful Post:
Southeast Power (03-27-2019)
Old 03-27-2019, 06:11 AM   #8
86 45 20
 
Southeast Power's Avatar
 
Join Date: Jan 2009
Location: Florida
Posts: 17,738
Rewards Points: 8,152
Default

Im concerned with the OP asking about 240 volts.
OP, are you concerned with the KW rating if the 3 phase generator is used single phase 120/240?
Southeast Power is offline   Reply With Quote
Old 03-27-2019, 08:18 AM   #9
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default

Quote:
Originally Posted by micromind View Post
Winding heat is dependent on amps; no part of any winding can be loaded beyond its amp rating.

KVA is amps and volts.

In your case, if you get power from the 240 point only, the gen becomes 62.5 KVA.

You are correct in that each winding can produce 150 amps, at 480 this will be 125 KVA. At 240, it'll be 62.5 KVA.

You can also use any combination of 240 and 480 loads provided no part of any winding produces more than 150 amps.

Be careful with the 240 here, it's not 120/240, it's 138/240 because it's connected Y.

Yes! thanks for the vindication on what I was trying to explain to my management & supplier.


I also didn't mention the 138/240 V result in my post, but I'm very happy that you noticed that outcome because that is exactly what we observed in our field test. In this generator configuration we have also attempted to provide some convenience receptacles (120V GFCI and 240 V) but then realized the 138V output !!

So again,, thank you for following this through to the same conclusion that I arrived at. That makes me feel relieved that I wasn't going nuts when they told me it could be done!
splatz likes this.
robg3987 is offline   Reply With Quote
Old 03-27-2019, 11:58 AM   #10
Senior Member
 
Bird dog's Avatar
 
Join Date: Oct 2015
Location: South East US
Posts: 4,963
Rewards Points: 1,700
Default

So, if you have a 480v genset, all you need is a 480v delta/208-120v xfmr?
https://www.platt.com/platt-electric...SubCatID=10980
glen1971 likes this.
__________________
Popcorn munching forum observer
"The supreme art of war is to subdue the enemy without fighting." Sun Tzu
Bird dog is online now   Reply With Quote
Old 03-27-2019, 12:23 PM   #11
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default

Quote:
Originally Posted by Bird dog View Post
So, if you have a 480v genset, all you need is a 480v delta/208-120v xfmr?
https://www.platt.com/platt-electric...SubCatID=10980
Yup,, that is what I had suggested also to solve the additional problem. But they don't seem to be interested nor heeding the technical advice provided. The main output would have to be turned down to around 415 volts to ensure there was 120 v available to the convenience receptacles. At 414 volts it becomes pretty much useless to any other motor loads connected.
So yes I agree the ideal solution was proposed as a xfr to handle the secondary loads at proper voltage.

The point I am at now, is to go to back to the actual manufacturer (Cummins) and get them to tell me what these windings are rated at. Then I can state my findings on the rated capacities and the configuration, if they want to exceed the ratings,,, then I can't do anything more.
robg3987 is offline   Reply With Quote
Old 03-27-2019, 12:46 PM   #12
Senior Member
 
Bird dog's Avatar
 
Join Date: Oct 2015
Location: South East US
Posts: 4,963
Rewards Points: 1,700
Default

Quote:
Originally Posted by robg3987 View Post
The point I am at now, is to go to back to the actual manufacturer (Cummins) and get them to tell me what these windings are rated at. Then I can state my findings on the rated capacities and the configuration, if they want to exceed the ratings,,, then I can't do anything more.
Present to Cummins your whole problem. They may say we do not recommend that, you can't do that or give you an acceptable option (do this or buy this kit).


Cummins may laugh at you & say buy a genset wth a 208/120v output.
glen1971 and Kevin_Essiambre like this.
__________________
Popcorn munching forum observer
"The supreme art of war is to subdue the enemy without fighting." Sun Tzu

Last edited by Bird dog; 03-27-2019 at 02:24 PM.
Bird dog is online now   Reply With Quote
Old 03-27-2019, 02:09 PM   #13
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default Dual Voltage Generator KsuggestVA & Amperage question

Lol,,,good point Bird Dog!
I appreciate all the input and suggestions.
Just waiting now for a call back from Cummins....
robg3987 is offline   Reply With Quote
Old 03-27-2019, 09:39 PM   #14
Junior Member
 
Join Date: Mar 2019
Location: Alberta
Posts: 9
Rewards Points: 14
Default

well, we heard back from the rep and they agreed with my assessment of reduced Kva at 240V (62.5 Kva).
All they would commit to in am email statement was ",,, with mid point tap of the series Y winding configuration the Kva rating would have to be de-rated from the 480V selection,,".
Now at least I have corroborated technical feedback, in addition to all of your feedback to support me.
Now if they want to override the ratings and damage it,, my conscious is clear that I did my due diligence.

Thank you all for your stellar input and advise.
Cheers!
Rob
robg3987 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
VA Low Voltage Question fayt Commercial Electrical Forum 9 04-11-2018 10:08 PM
Voltage Fluctuation Mr.Awesome PLCs, VFDs, Motors and Controls 45 03-20-2017 12:40 AM
Amperage question CuriousGeorge87 General Electrical Discussion 11 01-20-2017 11:22 PM
Chasing that voltage ~48~ Residential Electrical Forum 15 07-28-2016 12:26 AM
Cec voltage drop question Rick9999 General Electrical Discussion 7 05-15-2016 03:35 PM


All times are GMT -4. The time now is 06:31 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com