ANSI TR Insulator Nominal Voltages

[111R]

The ANSI TR numbers for station post insulators have standard nominal voltage ratings that jump from 15 kV to 23 kV to 34.5 kV. Due to this, I often see switches rated for 23 kV nominal, as well. I've noticed that 25 kV seems to be a very common distribution voltage rating, but I'm unsure of the rating required for insulators and switches at this system voltage. Many breakers in the U.S. are rated for 25 kV nominal and the standard maximum voltage rating is 27.6 kV. Above and below this equipment rating is 38 kV and 15.5 kV, respectively.

Which insulators are recommended for a 25 kV system? TR208 with a 23 kV nominal rating have a 150 kV BIL which seems to be more than sufficient for 25 kV nominal. TR210 insulators are rated at 34.5 kV which provides a safety margin for 25 kV, but they are much larger and I don't think I've ever seen this size of insulator on a 25 kV bay.

Any technical reference information will be appreciated. I've found ANSI C29.9, but it provides limited information. Is there an actual technical document on "ANSI technical reference numbers" that provides documentation on the recommended system voltages for given TR numbers?

 

[cuky2000]

111R,

Post insulator are selected not only for the BIL rating but also for the mechanical strength and the insulator creepage(leakage) distance required for a particular pollution environment. For high altitude applications, the insulators should be derated accordingly for both dielectric and creepage requirements.

In the ANSI/IEEE marketplaces, the insulators are designed by a TR (Technical Reference) numbers. Beware that some insulators do not have TR denomination but there are available in by some manufacturer. (See enclose example in the attached file).

See the enclosed file and links for basic info:

http://www.victorinsulators.com/stationpostindex.htm

http://www.victorinsulators.com/Drawings/Station Posts/1752.pdf

 

[switchguy]

Traditional grouping for air disconnect switches is 15 kV (TR-205 110 kV BIL), 23 kV (TR-208 150 kV BIL) and 34.5 kV (TR-210 200 kV BIL). There are specials but these groupings are predominant in the US. For many years air disconnects had a nominal and maximum design kV rating. For 23 kV nominal the maximum design rating was 25.8 kV and has recently been changed to 27 kV. A good reference for preferred ratings is IEEE C37.100.1-2007 which is a common clause document or the applicable standard for the type of switch that you are considering. For air disconnects the current standard is IEEE C37.30.1-2011.