Download SWER - NZ & Aust Experience

SWER
New Zealand & Australian
Experience
Prepared by John Tulloch
Presented by Ian Davies
Energy Week at the World Bank 2006
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What SWER Stands for ?
 SWER stands for Single
Wire Earth Return.
 Single wire system using
ground as return
conductor
 It is used for low cost
rural electrication
How it all started
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Lloyd Mandeno invented SWER in
New Zealand in 1925.
It was known as “Mandeno’s
Clothesline”. He called it “Earth
Working Single Wire Lines”.
Seen in 1940’s as preferred
solution for remote, sparsely
populated areas.
200,000 km of SWER now in NZ
and Australia.
How does it work?
Advantages of SWER
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Low capital cost
Design simplicity
Ease of construction
Excellent reliability
Low maintenance costs
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Limitations of SWER
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Restricted load capacity
Requirement for reliable low
resistance earthing at isolating and
distribution transformers
Possible interference with metallic
communications systems
Higher losses due to charging
currents
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SWER Basics
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Earthing requirements
Protection
Load densities
Voltage selection
Isolating transformers
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Earthing Requirements
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Reliability and design critical for
success
Earthing system conducts occasional
fault currents as well as continuous
load current
Particular care must be taken to
maintain continuity of earthing
system
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Protection
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With good earthing, adequate
protection viable even with low
fault currents
Standard drop out fuse
Standard HRC fuse
Circuit breaker with auto-reclose
Standard surge arrestor in lightning
prone areas
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Load Densities
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480 kVA with 25 Amp at 19.1 kV
Limited to 8 or 9 Amps in close
proximity (< 100 m) to open wire
metallic communication systems
Single phase motor loads
restricted to 22 kW (480V option)
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Voltage Selection
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19.1 kV based on operational
experience elsewhere
Easier to detect ground contact
faults
Operating voltage determined by
isolating transformer and not by
parent backbone feeder voltage
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Energy Losses
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Higher than conventional systems
Isolating transformer load and iron
losses offset in part by lower
losses in single phase
transformers
Higher impedence of SWER circuit
Charging current losses
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Communications Interference
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Earth return charging current
Proportional to line length. Typically
0.038 A / km
Harmonics from charging currents can
cause communications interference
Restriction of 8 to 10 amps in vicinity
(<100m) of metalic circuit
communications
Does not affect modern fibre optics or
radio communications
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Cost savings experienced in NZ
and Australia
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Same cost savings experienced in
both countries
Capital cost savings:
- 50% less than 2-wire, singlephase
-70% less than 3-wire, 3 phase
Estimated 50% maintenance cost
saving
Conclusion 1
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SWER is economical and simple to
design, construct and maintain
Main consideration is earthing
Only special equipment is isolating
transformer
Safe and reliable
Cost effective
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Conclusion 2
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Over 80 years of reliable
operation
Earthing problem resolved
Motors can be operated
Enough load capacity
Essential tool for low cost rural
networks
SWER
New Zealand & Australian
Experience
John Tulloch
Tulloch Consulting Ltd
Ph +64 7 8299911
Mobile +64 27 350 44 55 or +64 27 350 44 14
Fax +64 7 8299921
E-mail [email protected]
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