|
Four hundred homes in Southern African villages
now have mains power, thanks to an old technique
reworked by GIBB Africa. It will soon provide power
for thousands more homes.
The technique is single wire, earth return
(SWER): in other words, the power goes out along a
single wire, mounted on simple poles with long
spans, and then uses the earth as return. GIBB has
shown SWER can transmit power to small users in
outlying areas more cheaply than conventional
transmission with three conductor wires. Eskom, the
South African power company, expects to save about
£10 million in 1998 by using SWER.
Power is one of the modern amenities that many
South Africans yearn for. SWER means more of them
can have it soon.
Householders will use the same 230-volt lighting
and appliances as those supplied conventionally;
but the lines that carry power to their local
transformer will be SWER.
Australia and Brazil have used SWER for years to
take power long distances to outlying farms. Eskom
and the Botswana Power Corporation need to supply
customers who are closer at hand and greater in
number, but for whom they cannot justify a
conventional supply.
GIBB looked at the science and showed that SWER
could take higher currents and voltages than those
used in Australia, and that suitable switchgear and
other equipment were available. A GIBB system is
able to provide 500 kilowatts of power.
The 19,000 volts of the SWER line helps overcome
one of the problems of SWER, that of distinguishing
the normal return flow of power through the ground
from the abnormal flow when a conductor wire has
fallen and needs to be repaired. The voltage, and
South Africa’s insulation co-ordination standards,
also mean that SWER performs well even in the
presence of lightning.
GIBB has further had to show it can protect
people and animals from high voltages in the
electrodes connecting the SWER system to earth.
SWER is safer than conventional systems in one
important respect. If a conductor wire breaks, the
wire on the far side of the break cannot be alive
and unsafe.
So GIBB was able to persuade Eskom and Botswana
Power to adopt an unfamiliar technology. Botswana,
which had to change its regulations on the earthing
of power systems, decided on a £500,000 pilot
scheme, now nearly complete, for five villages near
its eastern border. It expects to use SWER for 60
more villages.
Eskom, where GIBB has trained staff, expects to
use SWER for more than half the 500,000 power
connections it plans for 1998.
|