×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Thermal effects of short circuit currents according to IEC standards

Thermal effects of short circuit currents according to IEC standards

Thermal effects of short circuit currents according to IEC standards

(OP)
Hi all!
Couple of questions about the subject.
Low voltage: Relatively new IEC 61439 standard defines rated short time withstand current Icw. It is the current which equipment or assembly can withstand for period of time given by manufacturer. Icw shall be equal to or higher than the prospective RMS value of the short circuit current Icp. It is explicitly stated that Icw is RMS value of AC component.
Medium/high voltage: There is a definition of Ik within IEC 60694 standard, practically the same as Icw, but without restriction to AC component, at least I didn't find any.
I am trying to make it clear which current within old (but precise and academic related) standards for calculation corresponds to particular values defined above. In other words, after short circuit calculation for given application, how to prove that some equipment or assembly may be safely installed regarding thermal effects of short circuit.

1. By my understanding of given definitions, Icp is closest to definition of initial symmetrical s.c. current Ik" given within IEC 60909. If so, then Icw/Ik shall be equal to or higher than calculated value of Ik", but then what is the purpose of duration of Icw/Ik, since Ik" doesn't depend on time?

2. There is a thermal equivalent short time current Ith defined within IEC 60865, as a value which is taking into account a thermal effect of DC component as well, and it depends on fault duration time, as it is physically logical. But what is the purpose of calculation of Ith if there isn't any standard value defined for equipment it may be compared with?

3. How can someone show (using IEC terms) that decreasing of fault duration by protection setting change will decrease thermal stresses as well and that same equipment can cope with s.c. for different protection setting, while it may fail for initial setting?

Back in old days, Ith and its duration for equipment or Joule integral was used, and everything was much more clear. Now I'm quite confused with all these values, but they are of course given as equipment data by manufacturers so I must comply. Please help.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close