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bytebyte (Electrical) (OP)
28 Dec 06 11:19
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 (Electrical)
28 Dec 06 12:33
Google CFO rating of electrical insulators
Helpful Member!  cuky2000 (Electrical)
29 Dec 06 23:21
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%20Types/9r.pdf
wareagle (Electrical)
30 Dec 06 9:42
Cuky
One way to increase the BIL is to use fiberglass pins instead of steel or wood. Would that do the trick?
cuky2000 (Electrical)
30 Dec 06 10:46
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.

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