Select Committee on Northern Ireland Affairs Sixth Special Report



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)CircuitsFaultsFaults per 1000 km**CICHL
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
12,73647,264

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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    Prepared 18 November 1999