Qufdoor immersed bushing

Qufdoor.immersed bushing

Bushing, one end of which is intended to be in ambient oirand exposed to outdooratmospheric condiions and the other end fo be immersedin an insulating medium other than ambient air (e.g. oil or gas).

Creepage distance

Shortest distance along the surface of an insulator between two conductive parts.

Minimum nominal creepage distance

Unless otherwise agreed between purchaser and suppler, or demonstrated by a fest, the creepage distance in accordance with lEC 815 s

determined by Ur(KV] x dcs (mm/KV) x kD where:

Ur: rate voltage valve

dcs: is the minimum nominal specifc creepage distance, the values of which for the varous pollution levels are.

I   light:  16 mm/Kv

Il  medium: 20 mm/Kv

lll  heavy: 25 mm/Kv

Iv  veryheavy: 31 mm/Kv

KD is the correction factor depending on the averaged diameter Dm of the insulator, the classes of which are

<300 mm:   KD=1

300 to 500 mm:  KD=1.1

>500mm:  KD=1.2

Dm: shall be determined in accordance with lEC 815.If artificial pollutions test are required they shall be performed in accordance with lEC 507

Arcing distance

Shortest distance in air extemal to the insulator between metalic parts which normaly have the operating voltage between them.

AltitudeAlthouah the insulaion level refers fo sea level, bushinas coresponding fo this siandard are declared suitable for operation at any aliludenot exceeding 1000 m, in order to ensure that the external withstand voltages of the bushing are suficient at altludes exceeding 1000 m, thearcing disfance normally required shall be increased by a suitable amounf. t is not necessary to adj ust the radial thicknes of insulation or theclearance of the immersed end. The punclure srength and the lashover voltage in the immersion medium of a bushing are not affectedby alfitude.To the limitalions of puncture srength and fiashover voltage in the immersion medium i may not always be posible to check the adequacyof the increased arcing dislance by aclual les at any altitude lower than that of operalion. in such a case the supplier shall demonslrale bythe amount of increase of the arcing distance, that the bushing is adequate.For general guidance an increase of 1,0% of the arcing distance necesary at sea level for each 100 min excess of 1000 m up to a maximumof 3000 m above sea level should be applied.EXAMPLE Alfitude of installation 2800 m:Increase in arcing distance.