Select Committee on Northern Ireland Affairs Second Report



  21. NIE has descr ibed the storm as "the most severe network emergency we have ever had to deal with." [26] Nearly 4,000 faults in all were reported over the period 26 to 31 December, over three quarters of them on 26 December. The overwhelming majority of faults causing loss of supply to customers occurred on the distribution system.[27] Numerically, the bulk of the faults were on the low voltage distribution lines, but the damage patterns were complex and multiple faults were c ommon. With the exception of the Belfast area, where relatively little of the electricity supply system is overhead, damage to the high voltage lines—the key element in the distribution network—was common across Northern Ireland. As we commented earlier, around 162,000 customers were affected on December 26, and, at the peak, around 110,000 customers were off-supply simultaneously.

  22. Other electricity supply undertakings also had serious supply interruptions. ESB reported[28] that, at the peak of the storm on 26 December, 185,000 customers lost supply. In ESB's Northern Region, which includes Ulster counties, North Connaught and North Leinster, 40% of customers lost supply.[29] In Great Britain, 120,000 customers supplied by Northern Electric were affected,[30] as were more than 240,000 supplied by Scottish Power[31] (at the peak, 125,000 simultaneously) and about 130,000 supplied by Norweb.[32] Northern Electric commented that "the extent of the damage in this storm was particularly challenging as it hit at all voltage levels on the network with numerous faults being created between a customer and a bulk supply point."[33]

  23. The complexity of the faults was cited by NIE as one of the reasons for the delays in restoring some consumers' supplies. By midnight on 26 December, around 63,000 customers remained off supply, and the last of them were not reconnected until New Year's Day. The progress of supply restoration for all customers over the period 26 to 31 December is set out in the Table below.[34]

Time band
0-3 hrs
3- 6 hrs
6-12 hrs
12-18 hrs
18-24 hrs
% restored
Time band
24-36 hrs
36- 48 hrs
48-60 hrs
60-72 hrs
% restored

  24. In the Republic of Ireland, there was a broadly similar pattern of supply restoration, as the Table below shows:[35]

Supply restored to
Still without supply overnight
26th December
1st January

  25. It is not possible to make detailed comparisons between the performance of the various electricity suppliers in restoring supplies to consumers following the storm without much more information about the nature of their supply systems, of the faults, and of the resources available to tackle them. However, it is clear that the experience of small numbers of consumers in Northern Ireland in being off-supply for long periods as a result of the storm was shared by consumers in Great Britain and in the Republ ic of Ireland in areas affected by similar storms.

  26. NIE has published an analysis of the faults causing power failures and their attributed causes. The majority (about 64%) were attributable to the wind, with just under a quarter being attributable to trees. The latter were of disproportionate significance in relation to faults on the low voltage network: 92% of all faults caused by trees affected the low voltage network.[36] Where damaged components were the direct cause of power failures, the majority of cases were attributable to conductor damage, and only 10% to pole damage. As a result of the storm, 1,133 poles were replaced out of a total of around 400,000—about 0.3%.[37] The vast majority had been broken [38] rather than pulled out of the ground. The typical age of damaged components was in the range of 20-40 years.[39]

  27. NIE drew attention to the significantly better performance of fully refurbished 11kV distribution circuits. It had previously concentrated its efforts in improving network reliability on the 11kV distribution circuits, as previous studies had shown that 70% of all fault-related customer interruptions occurred due to faults on this part of the network. The programme was prioritised to address the worst performing circui ts first, with circuits being ranked according to a combination of their fault rate and the number of customers affected. NIE maintains that the refurbished circuits performed significantly better in the storm than the unrefurbished circuits.[40]

26  NIE storm report, p. 3. Back

27  See paragraph 14 above. Back

28  Appendix 19, p. 83. Back

29  Appendix 19, p. 83. Back

30  Appendix 18, p. 83. Back

31  Appendix 16, p. 83. Back

32  Appendix 10, p.75. Back

33  Appendix 18, p. 83. Back

34  NIE storm report, p. 19. See Appendix 33, p. 119. Back

35  Appendix 19, p. 83. Back

36  NIE field staff reported that many of the tree-related faults were a direct consequence of overgrown trees in private gardens affecting low voltage overhead mains and services; see NIE storm report, p. 13. Back

37  0.47% on 33kV circuits, 0.23% on 11kV circuits and 0.45% on low voltage circuits. Back

38  Appendix 21, p. 100. Back

39  For NIE's comments on the relationship between the age of the network and its vulnerability to storm damage and an analysis of the correlation between age and failure rates in relation to poles damaged in the storm, see Ev. p. 29-31 and Appendix 21, p. 100-1. Back

40  NIE storm report, p. 10 and 14. Back

previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries

© Parliamentary copyright 1999
Prepared 29 July 1999