Minimise MV equipment failure – reduce lightning-related trips

A feeder’s lightning performance is measured against the number of trips due to lightning. This research was done by monitoring the Theunissen – Brandfort pumps 11 kV feeder’s performance (this is located in the middle of the Free State province, South Africa). The 300 kV BIL (Basic Insulation Level) design resulted in substantial damage due to wood splitting. Investigation undertaken shows that impulses due to lightning strikes with magnitudes of higher than 7 kA can cause splitting of the wood.

Replacing damaged wood poles results in customer outages. Sometimes the damaged pole is in very difficult or inaccessible terrain. It is therefore necessary to prevent wood splitting as far as possible. The detailed study was based on actual measurement of lightning (direct and indirect flashes) to investigate whether the BIL cannot be lowered by doing away with the bare wood gap.


Take Note

  • Much of our industry would qualify as small power users.
  • Many small power users are affected by lightning surges on the MV systems.
  • A new combi unit combines the benefits of over current and over voltage protection and can adequately protect a system from lightning surges.


Published as:

Lightning protection for equipment on MV feeders

By WJD van Schalkwyk and M du Preez, Eskom

Electricity+Control, October 2012 (pages 36 – 43))

• Willem van Schalkwyk:
• Mandri du Preez: Enquiries: