SWER New Zealand & Australian Experience

1. 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

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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) Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

13. 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

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 Mainstreaming Low-cost Innovations in Electricity Distribution Networks

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 +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