Transmission line insulation selection 2

[MEG1122]

Hello everyone

What governs the design of transmission line insulation? Switching surge overvoltage or lightning impulse.

 

[Mbrooke]

Bump

Good question.

Someone with better English can put it to words.

 

[argotier]

That is a very general question, so I'll give a very general answer (sadly I will not improve with the English part):

It depends on the rated voltage of the transmission line.

Up to 245 kV the lightning impulse is the most severe restriction.
Above 245 kV, switching impulse begins to be more important.

At least, this is the general view in the IEC world.

 

[cuky2000]

Transmission line design clearances include the conductor-to-conductor distances and conductor-to-ground as well associated with insulator assembly and swing separation to the metallic structures and shield wire to keep flashover and back-flashover strikes to acceptable levels.

For air Insulated transmission lines, also in the ANSI/IEEE zones, the Basic Insulation Level (BIL) governs the electrical clearances up to 230 kV. In contract, at 345 kV and above, the dominant effect is on switching surge effect to be withstood by the rated Switching Insulation level (BSL) directly related to the switching surge overvoltage factor (See NESC /IEEE Std C2). It should be noted that for gas Insulate lines (GIL) this may be different since is influenced by the fast transient reflecting wave effect (VFT).

The figure is a composite graphic with BIL and BSL include clearances for both the ANSI/IEEE and the IEC marketplaces.

I hope this satisfies your inquire.

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