×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Temporary overvoltages and surge arresters

Temporary overvoltages and surge arresters

Temporary overvoltages and surge arresters

(OP)
Hello everybody,

If a transformer neutral is grounded through a resistor to limit the magnitude of the single line to grund current, on the "healthy phases", there will be some overvoltages lasting the time overcurrent protection clears the fault.

Well, my question is related to these overvoltages:
Do surge arresters need to be sized considering them?

Because, in a case like this, they would have to be lower in MCOV and TOV than when neutral is solidly grounded.
Does anybody have some recommendations about it?

Any help/comment will be appreciated!

RE: Temporary overvoltages and surge arresters

For any resistance-grounded systems, the arresters should be rated as if the system is ungrounded.

The MCOV of the arrester for this situation must be HIGHER than a solidly-grounded system, not lower.

 

David Castor
www.cvoes.com

RE: Temporary overvoltages and surge arresters

Arrestor vendor information typically illustrates this point with different rating for solidly and resistively grounded systems.

RE: Temporary overvoltages and surge arresters

(OP)
Hello,
I thank your answers!
Any other comment will be welcome!

 

RE: Temporary overvoltages and surge arresters

The usual range of arrester MCOV rating is:
           1.05*VLGnominal ≤MCOV ≤ 1.10*VLLnominal
NOTE: For low MV and UHV, some application could select   MCOV > VLL        -- See first file --



As a rule of thumb, arrester MCOV rating usually is selected as follow:

     1) Ungrounded or impedance grounded:   MCOV ≈ 105% VLLnominal
     2) Solidly grounded:      MCOV ≈ 80% *VLLmax
 
To determine the actual TOV without using transient analysis, It is useful to use normalized curves to determine the Coefficient of Grounding (COG) or the Earth Fault Factor (EFF) (Both are equivalent EFF=1.73*COG)

The TOV (min MCOV) on the unfaulted phase for SLG fault could be determine as follow:

              MCOVmin= COG*(1.05 to 1.10* VLLNominal)

For additional details see the second enclosed files.
 

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!


Resources