1. SWER New Zealand & Australian Experience
Prepared by John Tulloch
Presented by Ian Davies
Energy Week at the World Bank 2006
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2. 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

3. 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.

4. How does it work?

5. Advantages of SWER Low capital cost Design simplicity
Ease of construction
Excellent reliability
Low maintenance costs
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6. 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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7. SWER Basics Earthing requirements Protection Load densities
Voltage selection
Isolating transformers
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8. 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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9. 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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10. 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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11. 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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12. 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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13. Communications Interference
Earth return charging current
Proportional to line length. Typically 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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14. 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

15. 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
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16. 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

17. SWER New Zealand & Australian Experience
John Tulloch
Tulloch Consulting Ltd Ph
Mobile or
Fax
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