ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Recent Posts
VFD MotorFeeders
by Yoopersup. 10/17/17 09:50 AM
What do you do?
by gfretwell. 10/17/17 01:08 AM
Good ol' copper pipe in the fuse holder trick
by HotLine1. 10/16/17 07:16 PM
Generator Cable Sizing
by HotLine1. 10/16/17 07:13 PM
Another generator question
by HotLine1. 10/16/17 07:02 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
241,338 Are you busy
177,289 Re: Forum
168,921 Need opinion
Who's Online Now
0 registered members (), 39 guests, and 7 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#187389 - 06/25/09 04:54 PM Is this transformer calculation correct?  
bigpapa  Offline
Member
Joined: Mar 2006
Posts: 81
canada
600v 3 phase to 120/208v 150kva dry type isolation transformer.
For some reason I need to be reminded of certain things that I have
forgotten over the years. Maybe someone can refresh me on this
transformer calculation.
Transformer is dry 150kva 3ph 600 to 120/208v isolation type.


Rated primary current is 144.5A
Primary breaker chosen is 150A therefore secondary current is 150x turns ratio of
2.88 which is 432A
Secondary conductors are 125% of RATED secondary current and
not actual secondary current which would be 416.6 x 1.25 = 520.8A.

I am thinking that secondary conductors are not calculated on the basis of actual secondary current but the transformers rated current.
Am I correct or have I missed something here?


Tools for Electricians:

#187395 - 06/25/09 08:52 PM Re: Is this transformer calculation correct? [Re: bigpapa]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 830
Michigan
This is a 480 volt 3 phase to 120/208 volt 3 phase right??
Also this is a feeder right???
1.73 x 480 = 830.4
150 x 1000 = 150000
150000 divided 830.4 = 180.63 amps primary
1.73 x 208 = 359.84
150000 divided by 359.84 = 416.85

then go to table 450.3(B)

That 600volts on Primary I think might be more like 480 volts.
Yoopers


#187398 - 06/25/09 09:32 PM Re: Is this transformer calculation correct? [Re: Yoopersup]  
bigpapa  Offline
Member
Joined: Mar 2006
Posts: 81
canada
Americans.


#187401 - 06/25/09 11:29 PM Re: Is this transformer calculation correct? [Re: bigpapa]  
twh  Offline
Member
Joined: Mar 2004
Posts: 919
Regina, Sask.
Rule 26-258: 125% of rated secondary current
150,000 / 208 / 1.732 x 1.25

primary conductors are also 125% in the same rule. It's the same calculation except 600 volts is substituted for 208 volts.

The same rule allows you to reduce the size to the demand providing... etc.

Overcurrent rules are in 26-256. Watch the ampacity of panels and splitters fed from transformers. They also must be rated for 125%.

For our Southern friends, 600/347 volts is common in Canada.



#187403 - 06/26/09 01:30 AM Re: Is this transformer calculation correct? [Re: bigpapa]  
jay8  Offline
Member
Joined: Jul 2005
Posts: 183
Vancouver, BC
Lets not turn this into some American bashing thing, his calculations are correct for secondary current. Maybe you forgot to use those little icons above each post.



Member Spotlight
Alan Belson
Alan Belson
Mayenne N. France
Posts: 1,803
Joined: March 2005
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.012s Queries: 15 (0.002s) Memory: 0.7680 MB (Peak: 0.9095 MB) Zlib enabled. Server Time: 2017-10-17 16:57:34 UTC