Choosing a Shed Profile for Contaminated Sites
Standard, fog, double umbrella and aerodynamic profiles each answer a different kind of deposit. Nominal creepage alone does not decide the choice.
Four Profiles, Four Deposit Types
Standard profiles are for clean inland air, giving 190 mm to 320 mm of creepage per disc. Fog profiles put extra creepage into deep under-ribs, reaching 400 mm to 550 mm, for salt and industrial fallout. Double umbrella profiles stack two skirts so fine dry dust cannot bridge the leakage path. Aerodynamic profiles use a wide open shed with no deep ribs so wind carries deposit away.
Nominal Creepage Against Effective Creepage
The aerodynamic LXAP-160 gives 380 mm of creepage against 550 mm on the fog profile U160BP at the same 160 kN rating. The aerodynamic unit is nevertheless the right choice on a remote wind-swept route, because its effective creepage stays close to the nominal figure while a dust-filled fog rib does not.
Check the Geometry Before Committing
Creepage is only half the decision. Shed diameter drives the swing envelope, from 175 mm on the smallest standard disc to 420 mm on the aerodynamic unit, and spacing drives the string length. Both figures are published per type so the tower window check can be done before the order.
Related Questions
Can we upgrade pollution class without changing the tower?
Often yes, by moving to a profile with more creepage per unit at the same spacing. The U160BP/155 for example gives 550 mm on a 155 mm spacing, so the string does not have to grow.
How often should contaminated strings be washed?
That depends on the deposit rate at the site. The point of selecting the right profile is to lengthen that interval, and changes in flashover history before and after are the practical measure.
Designs Referenced Above
Double umbrella disk Suspension Insulators UG120B146/450D 16R
120 kN Double Umbrella Disc for Heavy Contamination
View specifications
Glass Aerodynamic Profile Suspension Insulators LXAP-160 / U160A
160 kN Aerodynamic Glass Disc With a Self-Cleaning Shed
View specifications
Glass Fog Profile Suspension Insulators U160BP / 155
160 kN Fog Disc With 550 mm Creepage on a 155 mm Spacing
View specificationsRelated Categories
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