Frequently Asked Questions (FAQ)

The frequently asked questions below are based on emails received. I have edited out or changed names in some cases. I have also heavily edited some emails for clarity. While I am happy to answer queries on the use of SWER and on rural electrification in general, sometimes replies can be delayed.

SWER for Biomass Generation in India

Satya Maharshi Power Corporation Limited (SMPC) is a biomass electricity generation plant from agricultural waste. Currently we are generating 6 MW?? per hour. We are planning to establish another plant with same capacity. We happened to view your website and are curious to know more about your SWER. Can we distribute electricity for domestic and industrial purposes through: SWER? If yes, where or how can we inspect this technology? Where is your factory located? Because, we will have a bulk requirement and would like to personally inspect and discuss about SWER. Hope to hear from you soon. Sincerely, Gangadhar

Dear Sir,

The Rural Electrification Corporation of India, based in Delhi has standard distribution drawings and specifications that are ideally suited to rural electrification in India. From memory they also include a specification for SWER distribution transformers.

Single Wire Earth Return (SWER) Distribution Transformers, Specification Number 14/1979

http://recindia.nic.in/operstdn.htm

then follow the link on the left to construction standards, the Hindi version may be better

SWER is very much suited to either

a) sparsely populated rural areas or
b) rural areas and villages with low demand e.g. each house has only lighting, TV, radio and maybe small single phase induction motors for water pumping (1/4 horsepower or similar)

It is not really suited to industrial or commercial use as it is single phase and therefore it is difficult, but not impossible, to supply small to medium sized three phase induction motors.

To see designs that could be modified for use in India for SWER I suggest you download the engineering standards from

http://www.nt.gov.au/powerwater/business/connectioncode/pdfs_docs/standard_drawings

It would be better to use local Indian power poles and substitute Indian sourced materials (e.g. insulators, cross arms, transformers etc.) into the designs shown but the designs can be modified as needed to suit locally available materials.

see also;

http://en.wikipedia.org/wiki/Single_wire_earth_return

SWER in Nigeria

We would like more information on your low cost rural electrification. We need the service for a State in Nigeria.

Hi Elizabeth

Single wire earth return for low cost rural electrification is a useful way of electrifying rural areas which are either sparsely populated or where the demand per household is low e.g. lighting, radios, TVs and maybe a fridge.

It is not suitable for towns or villages with bigger loads. As a rule of thumb you can supply about 300 kVA per SWER circuit, up to about 80 km in length that is about 600 households with an average demand of 500 VA (roughly 500 Watts)

I am happy to advise and provide you with further information on SWER and rural electrification in general.

To further understand the concept, you may also like to review the Wikipedia article on Single Wire Earth Return (SWER) and the information contained in the downloads and links section of the site

Wood poles or concrete poles could also be considered to lower costs and/or make use of locally available materials.

SWER Insulators

I would appreciate any information on post insulators, post pin insulators, large angle post disc insulators. Could you advise where to obtain costs and supplier information please???

Hi Chris,

Post insulators and disc insulators are made by just about everyone; you could try morlynn insulators out of Australia or New Zealand Insulators

The majors egg Siemens, ABB, Schneider etc probably all do insulators.

One of the better insulator manufacturers is NGK of Japan. They have a plant in Indonesia that makes insulators which are good and relatively inexpensive.

People seem to be moving towards pin post insulators (rather than pin insulators) for 11 kV and 33 kV and polymer strain insulators.

How to Initiate a SWER Pilot Project

I will like you to give me details of how SWER could be utilised in a country where it has not been used or heard of before.

Hi Ajay

The best way would be to

1) Get some typical SWER drawings, designs and specifications to enable SWER to be installed, have a look at the downloads section for this
2) Carry out a pilot project involving a couple of villages to see if the technology is suitable for your situation

SWER Costs

In your paper on SWER (see downloads section), you calculated the cost per km of a distribution line. I would like to know what are the important parameters to consider when calculating the cost per km of a SWER distribution line with a pole spacing of 100m.

Hi Deborah,

When it comes to cost the level of importance are:

a) poles (the bigger the span, the less the cost as there are fewer poles) and then
b) conductor (span length has no effect on conductor cost)
c) labour costs, but this is a function of typical labour costs in each country e.g. high in North America, but lower in Africa

You should download "reducing the cost of grid extension for rural electrification" from the world bank web site www.worldbank.org it clearly outlines the cost factors to consider

SWER and Prepayment Metering Systems

We are in the process of finalising the technical specifications for pre payment metering system for use in domestic electricity supplies in India. We enclose a draft of the technical specifications for your review. In case you have any comments for suggestions kindly forward the same to us.

Hi Dinesh,

By far the most active prepayment metering standards originate from South Africa (SABS standards and NRS standards) you should look at these for a reference. You can download SABs standards by payment with a credit card over the internet. The main thing is to ensure interoperatability i.e. ensure that one manufacturer's prepayment meter will plug in to a common socket and will work with a billing/prepayment protocol defined by a standard

SWER for Rural Electrification in India

We are working on a project at Vijaywada in India where the power generated from biogas engine (3 Ph 125 kW) is exported to the grid. The supply company in Vijaywada is very reluctant to accept this power into the grid at 11KV. They allege there will be a lot of problem tripping due to fluctuations in frequency and voltage.

We would like to run a separate SWER line for supplying electricity to water pumps as the centrally generated electricity is unreliable and in any case they will not let connect the biomass generator to the existing 11 kV. Electricity is often used for pumping water, we are talking about pumps not exceeding 5 HP(3kw) power which can run on single phase

The MSEB ( Maharashtra state electric supply board) is trying to introduce single phase supply systems. The single phase power supply system is mainly for household consumers, I believe that SWER could be compatible with this concept.

Hi Vishwas,

It seems that water pumping is quite important. If there are existing three phase electric motors for running the pumps then you will need three phase power, i.e. SWER is single phase so can not be used for three phase (unless you buy expensive converters which defeats the purpose of SWER). As a rule of thumb only small induction motors of a maximum frame size of 5-10 kW can be run from single phase supplies, beyond this three phase motors are required.

If the power from the local grid is at 11 kV then you will have to have some sort of manual or automatic "change over switch" to switch between the central grid power and locally generated power. It will also be likely that your local generation will be at 400/230 volts so for loss of centrally generated power you will have to a) switch out the 11 kV b) switch in the local generators at 400/230 Volts. Alternatively you could switch out the power at a circuit breaker on the low voltage side of the distribution transformer and then start the local generator

SWER for Rural Electrification in Mali

I've learned about SWER systems while I was studying in Algeria, now I'm in Mali and promote small business in the rural electrification area, I would like more information on SWER systems and SWER equipment and your thoughts on the possibility of cooperation for training and implementation of SWER here.

Hi Diarra,

There is no really specialist equipment required for SWER. The transformers are a bit different so you should buy the Australian Standard AS 2558-1982 : "Transformers for use on single wire earth return distribution systems"

You also have to make sure the earthing is good and that may mean digging or drilling the earth rods in, especially in sandy soil. The poles, insulators, conductor etc. are similar to the equipment used for 22 kV or 33 kV distribution.

Please see the papers and downloads on SWER for further information.

You could also go to the Australia power and water website where they have drawings etc for SWER. They use steel poles but you could equally well use concrete or treated wood poles.

Rural Electrification using 33 kV

Please explain the concepts behind rural electrification using 33 kV rather than 22 kV, 11 kV etc.

Hi Merid

Although not common 33 kV can be used for rural electrification directly in the following manner

1) Distribute the medium voltage as two wire single phase 33 kV and then step it down using single phase two wire transformers 33/0.230 kV

2) Distribute the medium voltage as three wire three phase 33 kV and then step it down using 33/0.4 kV delta star tranformers (400 Volts phase to phase and 230 volts phase to neutral)

3) Distribute the medium voltage as SWER at 19.1 kV ( which is 33kV/sqrt 3 = 19.1 kV i.e. 19.1 kV phase to earth) and then step it down using a single phase 19.1/0.230 kV distribution transformer

35 kV systems are sometimes used for rural electrification in places such as Russia

SWER or SWGR Rural Electrification in Alaska

We have many isolated small communities in Alaska. We can not afford to interconnect them with conventional ac systems. We suggested SWGR (or SWER) but poor performance of an installation in Bethel makes agencies say SWGR is no good. We have areas of high resistance soils, up to 200kohms because they are frozen. Australia and S.Africa must also have: these types of conditions. Could you put us in contact with owners and operators of SWGR systems please

Hi Peter,

I can see with the earthing/grounding difficulties in Alaska SWGR may be problematic. I recently put in a new garage at home and a Canadian friend told me in Canada you would have to dig down below the permafrost to get good foundations it may be the same sort of idea to get a good earth/ground in Alaska.

The paper you need to read about SWER / SWGR earthing / grounding problems is

"Service experience with single wire earth return distribution systems in central Queensland" 7th CEPSI conference Brisbane Australia, 15-22 October 1988. They also had earthing problems but in the Outback it was due mostly to dry soils in summer, with the solution that you have to put your earths/grounds deep to get to the damp soil / ground water.

Please see the paper on SWER, the references may be of interest (located in the downloads section).

Another solution that may fit with the North American/ REA /USDA type of reticulation is to run a suspended neutral at the sending end with each pole and neutral grounded so you get multiple earths and to do the same at the receiving end, especially if the receiving end is a village and you are reticulating low voltage as well ( i.e. the expensive bit is the 16 - 120 kms in between with no suspended neutral/ground to save on costs). This would have the added benefit of fitting in more easily with established practice. The only downside I can think of is that a mid span break in the SWGR part would have no neutral to fall on and would not necessarily "trip" the line, if the ground/contact resistance is high.