Gantry dropper configuration
Gantry dropper configuration
(OP)
Currently designing a 220 kV SS, some designs implement gantry beam underhung insulator (I or sometimes V insulators) to support dropper from line side insulator string down to surge arrestor or disconnector.
The image below shows I string used for droppers as well as gantry jumpers.

I understand that for jumpers it is to avoid conductors encroaching clearances, however, for the dropper (The bay on right above), the dropper can go directly to the equipment below (mostly a voltage transformer).
what is the criterion for underhung string? is it to avoid clearances encroachment during wind blows? to slightly reduce the short circuit tensile forces on the equipment terminals below ( I don't see any major force reduction with U/H string)?
any clues?
The image below shows I string used for droppers as well as gantry jumpers.

I understand that for jumpers it is to avoid conductors encroaching clearances, however, for the dropper (The bay on right above), the dropper can go directly to the equipment below (mostly a voltage transformer).
what is the criterion for underhung string? is it to avoid clearances encroachment during wind blows? to slightly reduce the short circuit tensile forces on the equipment terminals below ( I don't see any major force reduction with U/H string)?
any clues?






RE: Gantry dropper configuration
RE: Gantry dropper configuration
• Underhung insulator is not required up to 10 m height
• For taller gantries, let’s say 19 m and above underhung insulator is suggested.
Considering the design wind speed, conductor tension, area, etc, the swing angle could be estimated by calculation or using software such as PLS-CADD.
See sample of substation layout typically used for 220 kV nominal voltage.
RE: Gantry dropper configuration
RE: Gantry dropper configuration
∅=tan-1(dc.F/12Wc)
where: dc = conductor diameter in inches; wc = weight of conductor in lbs./ft. F = wind force.
RE: Gantry dropper configuration
The swing angle will be useful for the two phases next to gantry legs. I think with wind blows, the inter phase clearances are usually kept intact as the three phases move together with the blow and return back and forth.
RE: Gantry dropper configuration
Additional information could found from a good transmission / substation line design. One reference that personally I use is Overhead Power Lines: Planning, Design, Construction by Friedrich Kiessling, Peter Nefzger, Joao Felix Nolasco, Ulf Kaintzyk. This reference has equation with and without insulator and graphic with swing angle as a function of wind speed.
Beware that for substation application, those equations need to be reconfigured to consider the drop down conductor tension without exceeding the maximum pulling forces on the connected equipment pad below the gantry.
RE: Gantry dropper configuration
RE: Gantry dropper configuration
RE: Gantry dropper configuration