mainstreaming low-cost innovations in electricity distribution networks 1 swer new zealand &...
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Mainstreaming Low-cost Innovations in Electricity Distribution Networks
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SWER
New Zealand & Australian ExperiencePrepared by John Tulloch
Presented by Ian DaviesEnergy Week at the World Bank 2006
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 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?
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Advantages of SWER
Low capital cost Design simplicity Ease of construction Excellent reliability Low maintenance costs
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Limitations of SWER
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
Earthing requirements Protection Load densities Voltage selection Isolating transformers
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Earthing Requirements
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
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
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
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
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
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
Cost savings experienced in NZ and Australia
Same cost savings experienced in both countries
Capital cost savings: - 50% less than 2-wire, single-phase-70% less than 3-wire, 3 phase
Estimated 50% maintenance cost saving
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Conclusion 1
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
Conclusion 2
Over 80 years of reliable operation
Earthing problem resolved Motors can be operated Enough load capacity Essential tool for low cost rural
networks
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SWER New Zealand & Australian
ExperienceJohn Tulloch
Tulloch Consulting LtdPh +64 7 8299911
Mobile +64 27 350 44 55 or +64 27 350 44 14Fax +64 7 8299921
E-mail [email protected]