×
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

Transformer Differential Protection (87)

Transformer Differential Protection (87)

Transformer Differential Protection (87)

(OP)
Should the transformer differential protection (87) be responsible on detecting single phase to ground faults inside the transformer? If there is a SLG on transformer secondary, should 87 detect it?

RE: Transformer Differential Protection (87)

Transformer differential protection can detect SLG faults.
Only thing is that the zero sequence filtering that is adopted in the protection settings desensitises the protection to some extent (makes it less sensitive in other words) against SLG faults.

RE: Transformer Differential Protection (87)

Need to back up to the "It Depends" stage of answering the question. What's the transformer? What are the "primary" and "secondary" winding configurations? (I like high-side and low-side much better than primary and secondary, they don't change with application.) Where in the winding is the fault?

Assuming that the "secondary" is a solidly grounded wye, most SLG faults will be detected by a phase 87 element. More can be detected by a negative sequence 87 element (called 87Q sometimes). But the closer you get to the neutral the harder it is for a phase 87 to detect. If the transformer is high impedance grounded, or capacitively grounded (aka ungrounded) then a SLG may not be picked up by the 87.

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

RE: Transformer Differential Protection (87)

Many new microprocessor differential relays have a Restricted Earth Fault (REF) function that can detect faults close to the neutral.

RE: Transformer Differential Protection (87)

That’s the theory anyway. Just found out the hard way just how susceptible REF can be to CT saturation on external L-L faults with a bit of neutral current. There is certainly a class of fault for which REF is the most definitive protection element, but to date I’ve seen more REF mistrips than correct operations. A bit jaded at the moment. But I must not be the only one, a major relay supplier recently revamped the REF in their advanced transformer relay. Firmware revision time…

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

RE: Transformer Differential Protection (87)

David,

That's interesting. It would be a good subject for a technical paper. I haven't seen any on the subject.

RE: Transformer Differential Protection (87)

Quote (David Beach)

That’s the theory anyway. Just found out the hard way just how susceptible REF can be to CT saturation on external L-L faults with a bit of neutral current. There is certainly a class of fault for which REF is the most definitive protection element, but to date I’ve seen more REF mistrips than correct operations. A bit jaded at the moment. But I must not be the only one, a major relay supplier recently revamped the REF in their advanced transformer relay. Firmware revision time…


Maybe a dumb question, but isn’t that what the stabilizing resistor is supposed to stop misoperations due to CT saturation??

RE: Transformer Differential Protection (87)

Low impedance REF, one of many functions of a transformer relay all using the same set of CT inputs. No way to include a resistor.

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

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