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

Changing current during a fault and overcurrent relays

Changing current during a fault and overcurrent relays

Changing current during a fault and overcurrent relays

How do microprocessor relays time their overcurrent elements when the fault current changes during the fault?

RE: Changing current during a fault and overcurrent relays

In essence they are "filling the bucket". Say you have a steady state fault current that results in tripping at 0.833 seconds and the relay process runs at 4 calculations per cycle. That means it's going to take 200 processor intervals to get to a trip, each interval adding .005 to the bucket. After 200 of those .005 results the sum is 1 and the trip is issued.

For varying currents, at each processor interval the relay accumulates some amount; take the trip time for the measured current and divide that into the length of the processor interval. Repeat until the sum gets to 1.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

RE: Changing current during a fault and overcurrent relays

Yeah, that is what I was expecting. It makes moving on the time overcurrent charts a little bit more complicated than sliding left and right.

RE: Changing current during a fault and overcurrent relays

The microprocessor simulates the integration that an electro-mechanical relay would do.

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


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