SWER New Zealand & Australian Experience Prepared by John Tulloch Presented by Ian Davies Energy Week at the World Bank 2006 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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?

Advantages of SWER Low capital cost Design simplicity Ease of construction Excellent reliability Low maintenance costs Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

SWER Basics Earthing requirements Protection Load densities Voltage selection Isolating transformers Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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) Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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

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 jetulloch@xtra.co.nz Mainstreaming Low-cost Innovations in Electricity Distribution Networks