It is currently Sun Apr 14, 2024 7:05 am

Author Message

 Post subject: Utilitys revisitedPosted: Mon Jul 12, 2010 4:40 am

Joined: Tue Feb 16, 2010 7:59 am
Posts: 21
Location: Minneapolis, MN
After numerous go arounds with a utility reluctant to provide available fault current data, and given our reluctance to storm the place with pitchforks and tourches, we were able to extract the following information:
The facility in question is fed from a substation with 3- 40 MVA transformers, "477 conductor" and nominal voltages of 139kV/12.4kV.
I am assuming that "477 conductor" means 477MCM and the conductor is almost certainly aluminum. We measured the transmission distance to the substation at 4.5 miles.
Now, a quick back of the envelop calculation using a table impedance value for 500MCM AL (wich is what I have handy) and guessing about 8% impedance for the transformer and 1% for the source, I am comming up with about 3800A which seems a fairly reasonable start.
My question is, Does anyone know what a reasonable impedance range for a 40MVA transformer might be.
Any input would be appreciated.

Bob Ragsdale, PE

Top

 Post subject: Posted: Wed Jul 28, 2010 8:26 am
 Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 622
Assuming the primary BIL is 550, ANSI C57.12.10 says 9.0% without load tapchanging and 9.5% with.

Note that with three transformers, there are three possible system configurations (source impedances) right there (neglecting all the other possible system changes the utility may make.)

Top

 Post subject: Posted: Wed Aug 11, 2010 3:52 pm
 Sparks Level

Joined: Mon Dec 14, 2009 4:24 pm
Posts: 61
I believe you mean C57.12.10

Top

 Post subject: Posted: Thu Aug 12, 2010 8:05 am
 Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 622
Fixed on edit. Thanks.

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 4 posts ]

 All times are UTC - 7 hours

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

 Jump to:  Select a forum ------------------ Forum Library / Articles The Lounge    Question of the Week - What Do You Think?    Arcflashforum.com Feedback and Announcements    Off Topic Discussions    News in Electrical Safety Arc Flash and Electrical Safety    General Discussion    Electrical Safety Practices    Equipment to Reduce Arc Flash Dangers    Personal Protective Equipment (PPE) Arc Flash Studies    General Discussion    Arc Flash Labels    Software for Arc Flash Studies    System Modeling and Calculations    NEW! Electrode Configuration Library â 2018 IEEE 1584 Codes and Standards    CSA Z462 Workplace Electrical Safety    EAWR Electricity at Work Regulations, HSE - Europe    OSHA CFR Title 29    IEEE 1584 - Arc-Flash Hazard Calculations    NFPA 70 - National Electrical Code - NEC (R)    NESC - ANSI C2 - National Electrical Safety Code    NFPA 70E - Electrical Safety in the Workplace    2015 NFPA 70E Share It Here    Arc Flash Photos    Your Stories    What's Wrong Here? by Joe Tedesco
© 2022 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883