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

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Presentation on theme: "Earthing of MV and LV Distribution Systems: A multi-faceted problem. Hendri Geldenhuys Gareth Stanford Industry Association Resource Centre (IARC) Eskom."— Presentation transcript:

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 Lines man safety considerations Merged with System protection and performance considerations

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

4 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, Design Philosophy

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

6 BIL wires on all shared structures (no gap no insulation of BIL wire.) BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.) No BIL wire BIL wire on all shared structures- insulate bottom 2m of down wire No BIL wire- Double arresters on transformers on MV side BIL wires on all – Move gap down below LV BIL wires on all – Split air gap above & below LV to prevent LV Faults

7 BIL wire on all shared structures (no gap no insulation of BIL wire.) LV Feeder MV Feeder Telephone

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

9 No BIL wire LV Feeder MV Feeder Telephone

10 LV Feeder MV Feeder Telephone BIL wire on all shared structures- insulate bottom 2m of down wire

11 LV Feeder MV Feeder Telephone No BIL wire- Double arresters on transformers on MV side

12 BIL wires on all – Move gap down below LV LV Feeder MV Feeder Telephone

13 LV Feeder MV Feeder Telephone BIL wires on all – Split air gap above & below LV to prevent LV Faults

14 Safety Risks That occurs in MV LV Distribution Systems

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

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

17 MV-LV Supply System L N E N

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

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

20 Equipment Damage

21

22

23

24

25 5 x I ph

26 Earthing and Bonding in different Environments Pollution Low Pollution High Lighting LowNo BIL down wire or bonding of hardware Bonding of hardware (no BIL down wire) Lighting HighBIL wire and co- ordinated gap Bonding of total structure, no gap, high insulator BIL.

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

28 AC power system related risk Design Philosophy MV Conductor drop onto LV system MV conductor contact to BIL down wire only LV contact to BIL down wire BIL wires on all shared structures (no gap no insulation of BIL wire.) Fast clearing of MV fault (1sec). Auto Reclose repeat to lock out. High GPR on LV Protective Earth. Exposure to all LV installations and BIL wire locations Med risk Slow clearing of fault (10 sec) even a small risk of not clearing fault. Very High GPR on BIL wire. Med risk Fault not cleared BIL wire stay live High risk BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.) Fault not cleared Fewer BIL wires stay live High risk No BIL wire Fast clearing of MV fault (1sec). Auto Reclose repeat to lock out. High GPR on LV Protective Earth. Exposure to all LV installations Med risk No risk BIL wire on all shared structures- insulate bottom 2m of down wire Slow clearing of fault (10 sec) even a small risk of not clearing fault. Very High GPR on BIL wire. Fault not cleared BIL wire not accessible Med risk No BIL wire- Double arresters on transformers on MV side No risk BIL wires on all – Move gap down below LV BIL wire will remain live until it flashes to LV protective earth. If Fault to LV occurs-clearing of the fault is the same as column to the left. Med risk Low risk BIL wires on all – Split air gap above & below LV to prevent LV Faults Low risk

29 Lightning risk Design PhilosophyEffective earth Public&Consumer lightning risk Equipment Damage BIL wires on all shared structures (no gap no insulation of BIL wire.) MV earth + LV earth +BIL wire earths. Best practice (not totally safe) Best Practice BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.) MV earth + LV earth +fewer BIL wires Best practice (not totally safe) Best Practice No BIL wire MV earth+ LV earth only High risk BIL wire on all shared structures- insulate bottom 2m of down wire MV earth + LV earth only Best practice (not totally safe) Best Practice No BIL wire- Double arresters on transformers on MV side MV earth + LV earth +BIL earths High riskMedium risk BIL wires on all – Move gap down below LV MV earth + LV earth + BIL earths Best practice (not totally safe) Best Practice BIL wires on all – Split air gap above & below LV to prevent LV Faults MV earth + LV earth + BIL earths Best practice (not totally safe) Best Practice

30 AC power risk Overall Risk Lightning Risk Design Philosophy MV Conductor drop onto LV system MV conductor contact to BIL down wire only LV contact to BIL down wire MV conductor contact to BIL down wire only LV contact to BIL down wire BIL wires on all shared structures (no gap no insulation of BIL wire.) MED HIGH LOW BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.) MED HIGH LOW No BIL wire MEDLOW HIGH BIL wire on all shared structures- insulate bottom 2m of down wire MEDLOWMED 2 MED LOW No BIL wire- Double arresters on transformers on MV side MEDLOW HIGH MED BIL wires on all – Move gap down below LV MED 3 MED LOW BIL wires on all – Split air gap above & below LV to prevent LV Faults MEDLOW 1 MED LOW

31 LV Feeder MV Feeder Telephone 50 mmLVgap 500 mmBILwood gap

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


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