Earthing of MV and LV Distribution Systems: A multi-faceted problem.

1. Earthing of MV and LV Distribution Systems: A multi-faceted problem. Hendri Geldenhuys Gareth Stanford Industry Association Resource Centre (IARC) Eskom

2. Considerations related to: Public , Customer (end user?) And Line’s man safety considerations Merged with System “protection” and performance considerations

3. MV Line LV Feeder Distribution transformer LV Earth MV Earth Service Box Communication Service line connection Artwork: A Dickson

4. Design Philosophy Consider the Bonding and Earthing of the structure: • There are no single solution that fits all applications and environmental conditions • All solutions has risk, some less than others,

5. Design Philosophy MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder Wood, Concrete LV Feeder or Steel Telephone

7. BIL wire on all shared structures (no gap no insulation of BIL wire.) MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

8. BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.) MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

9. No BIL wire MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

10. BIL wire on all shared structures- insulate bottom 2m of down wire MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

11. No BIL wire- Double arresters on transformers on MV side MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

12. BIL wires on all – Move gap down below LV MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

13. BIL wires on all – Split air gap above & below LV to prevent LV Faults MV Feeder Wood, Concrete LV Feeder or Steel Telephone MV Feeder LV Feeder Telephone

14. Safety Risks That occurs in MV LV Distribution Systems

15. Separate MV and LV Earths FEEDER LINE ( 3Ph , Ph-Ph or SWER ) TANK fuses SURGE ARRESTOR + 242 V - 242 V N HV TO LV NEUTRAL ARRESTOR L N E LV EARTH MV EARTH

16. MV Voltage Transferred to LV Earth FEEDER LINE ( 3Ph , Ph-Ph or SWER ) TANK fuses SURGE ARRESTOR + 242 V - 242 V N > 5 kV HV TO LV NEUTRAL ARRESTOR > 5 kV L N E LV EARTH MV EARTH

17. MV-LV Supply System L N E N L N E

18. MV-LV Supply System N L N E L N E L N E L N E 2.5 kW 10A 2.5 kW 10A 100V -100V -100V 100V 20A LV Neutral Break

19. LV MV 161 V [ =230 x (70/100) ] I = 2.3 A 69 V [ =230 x (30/100) ] Neutral SA ☻The ratio between the MV and LV earth electrode resistance determine the voltage on the LV neutral- earth 70 Ω 30 Ω Step potential

20. Equipment Damage

25. 5 x Iph

26. Earthing and Bonding in different Environments

27. MV Line LV Feeder Distribution transformer LV Earth MV Earth Service Box Communication Service line connection Artwork: A Dickson

31. MV Feeder 500 mm BIL wood gap LV Feeder 50 mm LV gap Telephone MV Feeder 500 mm BIL wood gap LV Feeder 50 mm LV gap Telephone

32. A (simple) Wood Pole Structure has complex safety and performance considerations • Designs can be optimised for specific areas and applications • No Power System is ever 100% safe

33. Safe and Reliable