Substation vertical dropper swing angle under wind blow 3

[Power0020]

How can the vertical dropper conductor movement/swing angle be estimated under wind blow? I have seen formulae for estimation of vertical insulator jumper movement under wind, but not the vertical dropper near to gantry.

this is to check available phase-to-ground clearance next to gantry leg.

 

[jghrist]

IEEE Std 605-2008, IEEE Guide for Bus Design in Air Insulated Substations, has a method for calculating conductor swing of strain bus. For vertical drop jumpers, you will have to estimate the forces involved and do a statics analysis. A lot depends on how the ends are supported. Don't forget that there will be short circuit forces as well as wind.

 

[prc]

Let me caution on this vertical dropper especially used with power transformers. I have seen many transformer failures from improper dropper connections. Two samples:
1) Year 2010 - A 315 MVA 420 kV auto transformer failed in early hours at ambient temperature of 2C. One of the 420 kV bushing lower porcelain cracked and bushing flashed at tail end. Since it was under oil with out causing tank rupture, no fire erupted. The ACSR dropper connection from bushing top terminal to aluminum bus was done with a short length conductor with out sufficient slackness. Ambient was above 45C when the connection was provided. Failure occurred during the first winter when temperature was minimum. Tremendous pull on bushing terminal from temperature variation seems to be the cause of failure.
2)Year 1984- India's first 500 MW thermal set was commissioned. The 600 MVA GSU bank was provided with RIP (dry type) 220 kV condenser bushings. With in couple of weeks, porcelain of bushing broke. No fire or tripping, thanks to dry type condenser bushings. Here the dropper connection was to middle of a long catenary bus. During the wind or line fault, the catenary swung violently, causing very high pull on bushing terminals. Solution: connect dropper to end of catenary with sufficient slackness in the dropper.