×
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

11KV Cable Test

11KV Cable Test

11KV Cable Test

(OP)
Could anybody tell me what the minmium value of insulation resistance an existing 11KV cable should be when tested phase to earth at 5KV test voltage?

We have recently had an 11KV panel off for maintenance, when we came to restore power we tested the panel bus bars & the feeder cable together (as there is a joint in the feeder cable which is suspect).

Red & Blue phases were over 500Mohm to earth & Yellow phase was 130Mohm to earth (similar readings were recorded between phases).

The switchgear is ancient AEI oil filled, & the instruction manuals quote a minimum of 100Mohm to earth at 5KV test voltage.

Do current standards require the same value?

We succesfully restored power but will in due course replace the cable.

RE: 11KV Cable Test

We would accept 100MOhm for cables that have been in service and have been taken out for maintenance reasons or for IR tests after a fault.  We also have a level of 5MOhm that we will put back into service, but will ensure we plan to replace the cable (or sections at least) within the near future.

Don't forget also that you are not just testing the cable, but also the insulation in the switchgear as well.  This may well be the limiting factor of the IR in your measurement.  However, if your switchgear manual says 100MOhm, and your total measurement including cable and switchgear is 130MOhm, then you can be sure that your switchgear and cable are both above 100MOhm.

RE: 11KV Cable Test

A maintenace thumb rule is, highest system voltage plus 1 Mohms. If you are measuring IR of 11KV system phase with 5KV megger then you should have HSV+1= 12+1= 13Mohms to arrive at a firm decision to apply normal voltage to equipment ( charging).

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