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


Difference in BIL and CIFO ratings

Difference in BIL and CIFO ratings

Difference in BIL and CIFO ratings

The utility company that I work for requires our customers to maintain a BIL of 120kV for 15kV service. The customer wants to install a pin insulator with a CFO rating of 105kV.

I noticed that the distribution insulators are rated according to their CFO value instead of BIL value.  CFO is the voltage at which the probability of flashover is 50% and BIL is the measure of the ability of the insulation system to withstand very high voltage surges.  But what is the conversion or relation between CFO and BIL?  Thanks.

RE: Difference in BIL and CIFO ratings

Google CFO rating of electrical insulators

RE: Difference in BIL and CIFO ratings

The pin insulator rated for a critical flashover voltage CFO=105 kV do not meet the utility requirement in term of basic insulation level BIL=120kV. This is because the ratio K=CFO/BIL is less than 1. I presume that pin type insulators is also similar to post type insulator with K=0.94

A practical suggestion to the costumer is to work with the utility submitting in advance the type of insulator to be replaced. A sample of suggested pin insulator is one similar to the ANSI class 55-5 rated for positive flashover impulse of 130 kV.  This will provide a margin of 8% to reduce the CFO to produce a withstand level roughly within the BIL rating requirement of 120 kV.


RE: Difference in BIL and CIFO ratings

One way to increase the BIL is to use fiberglass pins instead of steel or wood. Would that do the trick?

RE: Difference in BIL and CIFO ratings

Hi Wareagle,

Your suggestion is one way to be considered. However, the effort to convince the utility usually may not justify the delay and cost associated with this task.

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!


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