132KV CABLE VERSUS 132KV OVERHEAD LINE (8KM) FOR THE PONGOLACANDOVER ESKOM DISTRIBUTION POWER LINE PROJECT
The option of installing an underground cable system compared to an overhead line for 8km along the
Pongola – Candover line was not technically feasible due to the following reasons:
a) Cable costs are much higher than overhead lines due to the amount of copper and insulation
used in the construction of cables. Trenching costs are also much higher depending on the
type of soil.
b) Cables require additional infrastructure in the form of a “Sealing end substation” that is used
as an interface between cable and overhead lines. This requires additional land use and
environmental requirements.
c) Cables have a longer repair time due to fault finding and trenching to repair the fault. The
recent cable failure at the Richards Bay Coal Terminal is a typical example of a 7-10 day
repair time depending on available skills and the nature of the fault.
Estimated 132kV cable costs (80% normal, 20% rock):
SUMMARY
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
Prelimary and General Cost, and Site Establishment
Health and Safety
River Crossings
Road Crossings
HV Cable : Civil Installation
HV Joints bays: Civil Installation
Cable route markers
Removal of existing HV cable
HV cable: Electrical Installation
HV Joints and Kiosks: Electrical Installation
HV Cable Terminations: Electrical Installations
Installation of Distributed Temperature Sensing (DTS) system and protection fibre circuit
Re-instatement
Testing
As-built drawings
Transport
Material - 132kV Cable
R
R
R
R
R 2 011 300.40
R
786 568.90
R
13 843.80
R
R
483 104.00
R
611 900.44
R
322 327.35
R
287 410.00
R
864 084.98
R
194 448.07
R
35 800.00
R
109 732.50
R 4 368 000.00
TOTAL R 10 088 520.44
For 80% rock and 20% normal soil, add R450,000 (estimated) for labour and disposal of rock under
section E (HV Cable: Civil Installation) in table above. No P&G’s and Health Safety included.
Estimated 132kV Overhead line costs
R1.5mil per km without P&G’s
132kV cable costs
(80% normal, 20%
rock):
132kV cable costs
(20% normal, 80%
rock):
132kV Overhead line
(80% normal, 20%
rock):
132kV Overhead
line (20% normal,
80% rock):
R 10mil
R 11.5mil
R 1.5mil
R 1.3mil
Area Disturbed and Rehabilitation Costs – Financial as well as Environmental
For cabling an area approximately 15m wide is cleared to facilitate trenching, stockpiling of excavated
material from the trench, which is 1-2m deep (variable dependent on circumstances) X 1m wide, and
to accommodate a service road during construction. This will have to be actively rehabilitated by
watering and weeding with pursuant passage over the landowners’ properties, at an exorbitant cost,
over a lengthy period of time, once construction has been completed. It is unlikely that the original
climax vegetation type and its diversity will reestablish which could take up to one hundred years or
more to transpire. Spoil will have to be transported at cost away from site and deposited in an
authorized area. Authorization often involves further assessment and project delays as a result.
This is opposed to the 132kV overhead line where an area at the tower base will be cleared of
vegetation of a maximum dimension of 40mX40m every 350m in flat terrain. Holes will be dug for the
self-supporting steel structures equivalent to 12m3 or equivalent to 16m3 for steel guyed structures.
Spoil is minimal and topsoil can be spread around the site once construction is complete. For overhead
lines access tracks are cleared of vegetation and seldom have to be shear cleared, except in steep,
inaccessible terrain, where access roads may have to be created or construction conducted by some
other means such as by helicopter or by hand. Access tracks are normally created by driving to and
from the towers. Bushclearing down the line is undertaken merely to accommodate stringing the
conductor. Little shear clearing of the top soil and removal of roots of vegetation and disturbance or
loss of the seedbank in the top soil is incurred making rehabilitation easier and thereby simultaneously
reducing erosion potential when compared with cabling. Soil compaction transpires around tower
bases and on access tracks which requires remediation but, proportionally, nowhere near to the
magnitude that is required to rehabilitate excavated areas for cabling. Biodiversity is largely
maintained as a result and rehabilitation, which remains costly, is completed in a relatively far shorter
period of time – months as opposed to years.