Difference in BIL and CIFO ratings 1

[bytebyte]

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.

 

[wareagle]

Google CFO rating of electrical insulators

 

[cuky2000]

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.

http://www.victorinsulators.com/Drawings/Pin Types/9r.pdf

 

[wareagle]

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

 

[cuky2000]

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.