APPENDIX B
Analysis of HV Faults—8/19 September 1999
(based on NAFIRS data available 11.10.99)
1. Analysis by Network Voltage
| Network | Faults | Customer
Interruptions (CI) | Customer
Hours Lost (CHL) |
| 33 kV | 9 (14%) | 5,282 (29%) | 9,101 (16%) |
| 11 kV | 54 | 12,736 | 47,264 |
| Total | 63 | 18,018 | 56,365 |
Note: 11 kV—60 NAFIRS entries (including
4 "supply infeed failures to neighbouring districts"
and 2 "extension of fault zone" entries)—54
separate faults excluding above duplicates.
2. 11 kV Faults—Analysis by degree of
refurbishment
| Category | | Data for 18-19 September 1999 |
| | Population (km) | Circuits | Faults | Faults per 1000 km** | CI | CHL |
| Complete | 1,155 (6%) |
2 | 2 | 1.7 | 122 | 250 |
| Complete* | 1,800 (9%) | 1 | 1 | 0.6 | 70 | 74 |
| Partial | 4,457 (22%) | 15 | 18 | 4.0 | 4,458 | 10,374 |
| None | 12,660 (63%) | 30 | 33 | 2.6 | 8,086 | 36,566 |
| Total | 20,072 | 48 | 54 | 2.7 | 12,736 | 47,264 |
Complete* includes those circuits that have been
completely refurbished but part of which was—carried out
to the pre-95 specification.
Faults per 1000 km**—No. of faults normalised against circuit
length in population.
3. 11 kV Faults—Analysis by cause and
refurbishment category
| Cause | Refurbishment Category
| Total |
| | None | Partial | Complete | Complete* | |
| Wind/Gales | 12 | 12 | 0 | 0 | 24 |
| Trees | 11 | 1 | 1 | 0 | 14 |
| Unknown | 9 | 2 | 0 | 1 | 12 |
| Age-Wear | 1 | 3 | 0 | 0 | 4 |
| Totals | 33 | 18 | 2 | 1 | 54 |
Note: Faults attributed to "trees"
includes both those assigned as either Direct or Contributory
Cause in NAFIRS.
Comments
In assessing the performance of refurbished circuits
the following points should be borne in mind:
There are
obvious dangers in basing definitive conclusions on a relatively
small sample size.
Having expressed
this caveat, the analysis does suggest that those circuits that
have been completely refurbished performed significantly better.
The circuits
that have been partially refurbished performed worse than those
with no refurbishment. This is because inherently, the circuits
on which work is in progress are rogue circuits which by their
nature are the worst performing. In addition, this also demonstrates
that the benefits of refurbishment do not become apparent until
the circuit is completed.
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