Lightning Outages on 25kV Underground Distribution System

[distributionPlanner]

Lightning frequently causes outages on 25kV overhead systems.

Has anyone heard of lightning causing outages on 25kV underground systems?

 

[pwrengrds]

There could be ground currents depending on how the system is set up it could cause faults.

If the shields are grounded at both ends and the shield is wired through the CT it can cause tripping problems also (but that's a wiring mistake).

 

[stevenal]

Those UG systems generally connect to overhead systems. Unlike the air insulation of the overhead system, the UG cable insulation will not recover following an overvoltage. Arresters are needed to prevent cable insulation damage and extensive outages caused by lightning.

 

[Power0020]

I didn't hear about that actually, it is very common to install surge arrestors just behind the cable termination connecting to overhead lines interface point.

On other hand, the cables BIL are usually higher than OHTL so it is rare that a lightning wave will propagate past a line towards a cable without flashing the overhead line insulators.

One case may occur is a ground inducted current (due to nearby lightning discharge) with high di/dt causing induced voltage on the sheath and core as well?, I am not aware of the magnetic model for cables but can say that if the sheath is solidly (two points) grounded, you should not worry about it.