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| Business and sustainability performance review |
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| SECURING CONTINUITY OF SUPPLY |
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| Distribution system performance |
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As the prior year performance and targets did not include major load shedding events, the current
year performance has been adjusted
and disclosed separately for analysis and comparative purposes.
Distribution network interruption measures |
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| Measure |
Description of measure
(and unit) |
Target
2008
(exclude
load
shedding) |
Actual
2008
(exclude
load
shedding) |
Actual
2008
(include
load
shedding) |
Actual
2007
(include
load
shedding) |
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Comments |
| Distribution supply loss index
(DSLI) |
Transformer unavailability index (minutes per month) |
≤5,10 |
10,36 |
31,50 |
9,10 |
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| Reticulation supply loss index
(RSLI) |
Total transformer unavailability
index (hours per annum) |
≤ 1,55 |
2,24 |
3,39 |
1,95 |
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| Reticulation supply loss index
(RSLI) |
Unplanned transformer
unavailability index
(hours per annum) |
≤1,10 |
1,68 |
2,82 |
1,33 |
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See combined
explanation below
for DSLI, RSLI, SAIfi and SAIDI |
| System average interruption
frequency index (SAIfi) |
Reliability of supply index
(number per annum) |
≤ 22,80 |
25,36 |
33,72 |
25,20 |
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| System average interruption
duration index (SAIDI) |
Availability of supply index
(hours per annum) |
≤42,30 |
55,51 |
73,70 |
51,40 |
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Comments regarding SAIDI, SAIfi, DSLI and RSLI
Performance has not improved since the previous year and the
business plan target was not achieved due to a higher number
of planned interruptions for maintenance and refurbishment and
an increase in unplanned interruptions, caused by an increase in
conductor theft, energy theft and bad weather. Load shedding
also had a negative impact on operational performance.
Benchmarking Distribution’s performance
Distribution has participated in benchmarking panels in North
and South America. The network characteristics and operational
processes/practices of the distributors in the benchmarking panels
are not the same, which results in a wide range of performance
levels.
Eskom’s network interruption performance is dominated by the
performance of our rural lines, which have historically been built
on a least-cost basis. In this respect, Eskom’s distribution networks
differ significantly from those of other distribution companies
that have areas of supply that include large cities and towns. Most
rural lines in South Africa are long radial lines with very limited
redundancy and back-feed capability. This significantly distorts any
comparison to North American distributors in the benchmarking
panel.
SAIDI performance in South America (2007) is between
3,5 hours and 90 hours per annum and SAIDI performance
between 2,5 and 60 events per annum. Benchmarks for DSLI and
RSLI do not exist.
Distribution quality of supply measures |
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| Measure |
Description of measure
(and unit) |
Target
2008 |
Actual
2008
(exclude
load
shedding) |
Actual
2008
(include
load
shedding) |
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Actual
2007 |
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Comments |
| Regulation1 |
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≥97,00 |
96,20 |
96,20 |
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99,00 |
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Not achieved – deviations
from nominal supply voltage
at a few sites.
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| Unbalance2 |
Waveform quality
of supply index
(%) |
≥94,00 |
95,20 |
95,20 |
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99,50 |
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Exceeded – the three
phases of supply voltage are
electrically balanced |
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| Harmonics3 |
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≥94,00 |
91,20 |
91,20 |
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98,90 |
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Not achieved – unable
to avoid higher-order
frequencies at a few sites |
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| Type X dips4 |
Disturbance quality
of supply index
(%) |
≤51,00 |
29,70 |
29,70 |
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30,50 |
Exceeded – faults and
breaker operations at the
various voltage levels are
under control |
| Type S dips4 |
≤48,00 |
28,70 |
28,70 |
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18,90 |
| TypeT dips4 |
≤48,00 |
25,30 |
25,30 |
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28,70 |
| Type Z dips4 |
≤48,00 |
22,70 |
22,70 |
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24,40 |
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Click here for more information on the distribution performance measures. |
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1 Regulation reflects the ability to control deviations from the nominal supply voltage contracted with customers.
2 Unbalance reflects the ability to keep the three phases of the supply voltage electrically balanced, that is,
displaced by 120° relative to one another and the same magnitude.
3 Harmonics reflects the ability to avoid higher-order frequencies in the 50Hz supply voltage.
4 Disturbance quality reflects the ability to minimise faults and breaker operations at various voltage levels. |
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