Earthing of MV and LV Distribution Systems: A multi-faceted problem. Hendri Geldenhuys Gareth...
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Transcript of Earthing of MV and LV Distribution Systems: A multi-faceted problem. Hendri Geldenhuys Gareth...
Earthing of MV and LV Earthing of MV and LV
Distribution Systems: Distribution Systems:
A multi-faceted A multi-faceted
problem.problem. Hendri Geldenhuys
Gareth Stanford
Industry Association Resource Centre (IARC) Eskom
Considerations related to:Public , Customer (end
user?)And Line’s man safety
considerations
Merged with
System “protection” and performance considerations
Artwork: A Dickson
LV Earth
LV Feeder
Service Box
Serviceconnection
Communicationline
Distributiontransformer
MV Earth
MV Line
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
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel
Design Philosophy
Design PhilosophyBIL 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 wireBIL wire on all shared structures- insulate bottom 2m of down wireNo BIL wire- Double arresters on transformers on MV sideBIL wires on all – Move gap down below LVBIL wires on all – Split air gap above & below LV to prevent LV Faults
BIL wire on all shared structures (no gap no insulation of BIL wire.)
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.)
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
No BIL wire
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
BIL wire on all shared structures- insulate bottom 2m of down wire
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
No BIL wire- Double arresters on transformers on MV side
BIL wires on all – Move gap down below LV
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
LV Feeder
MV Feeder
Telephone
Wood,
Concrete
or Steel LV Feeder
MV Feeder
Telephone
BIL wires on all – Split air gap above & below LV to prevent LV Faults
Safety Risks That occurs in MV LV
Distribution Systems
Separate MV and LV Earths
L N E
TANK
N
- 242 V+ 242 V
LV EARTH
HV TO LV NEUTRAL ARRESTOR
SURGE ARRESTOR
MV EARTH
FEEDER LINE ( 3Ph , Ph-Ph or SWER )
fuses
MV Voltage Transferred to LV Earth
L N E
TANK
N
- 242 V+ 242 V
LV EARTH
HV TO LV NEUTRAL ARRESTOR
SURGE ARRESTOR
MV EARTH
FEEDER LINE ( 3Ph , Ph-Ph or SWER )
fuses
> 5 kV
> 5 kV
MV-LV Supply System
L N E
N
L N E
MV-LV Supply System
L N E
N
L N E L N E L N E
2.5 kW10A
2.5 kW10A
20A
-100V -100V 100V 100V
LV Neutral Break
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) ]
Equipment Damage
5 x Iph
Earthing and Bonding in different Environments
Pollution LowPollution High
Lighting Low No BIL down wire or bonding of hardware
Bonding of hardware (no BIL down wire)
Lighting High BIL wire and co-ordinated gap
Bonding of total structure, no gap, high insulator BIL.
Artwork: A Dickson
LV Earth
LV Feeder
Service Box
Serviceconnection
Communicationline
Distributiontransformer
MV Earth
MV Line
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 locationsMed 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 clearedBIL wire stay live
High risk
BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.)
Fault not clearedFewer 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
installationsMed risk
No 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 clearedBIL wire not accessible
Med risk
No BIL wire- Double arresters on transformers on MV side
No risk 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 Low risk
Lightning risk
Design Philosophy Effective earthPublic&Consumer
lightning riskEquipment 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 wireMV earth+ LV earth
onlyHigh risk 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 risk Medium 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
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 MED HIGH HIGH LOW LOW
BIL wires only on suspension structures with no stays (no gap no insulation of BIL wire.)
MED MED HIGH HIGH LOW LOW
No BIL wire MED LOW LOW HIGH HIGH HIGH
BIL wire on all shared structures- insulate bottom 2m of down wire
MED LOW MED 2 MED LOW LOW
No BIL wire- Double arresters on transformers on MV side
MED LOW LOW HIGH HIGH MED
BIL wires on all – Move gap down below LV MED MED MED 3 MED LOW LOW
BIL wires on all – Split air gap above & below LV to prevent LV Faults
MED LOW LOW 1 MED LOW LOW
LV Feeder
MV Feeder
Telephone
50 mm LV gap
500 mm BIL wood gap
LV Feeder
MV Feeder
Telephone
50 mm LV gap
500 mm BIL wood gap
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
Safe and Reliable