Seismic performance of buried electrical cables: evidence-based repair rates and fragility functions

Abstract

The fragility of buried electrical cables is often neglected in earthquakes but significant damage to cables was observed during the 2010-2011 Canterbury earthquake sequence in New Zealand. This study estimates Poisson repair rates, similar to those in existence for pipelines, using damage data retrieved from part of the electric power distribution network in the city of Christchurch. The functions have been developed separately for four seismic hazard zones: no liquefaction, all liquefaction effects, liquefactioninduced settlement only, and liquefaction-induced lateral spread. In each zone six different intensity measures (IMs) are tested, including peak ground velocity as a measure of ground shaking and five metrics of permanent ground deformation: vertical differential, horizontal, maximum, vector mean and geometric mean. The analysis confirms that the vulnerability of buried cables is influenced more by liquefaction than by ground shaking, and that lateral spread causes more damage than settlement alone. In areas where lateral spreading is observed, the geometric mean permanent ground deformation is identified as the best performing IM across all zones when considering both variance explained and uncertainty. In areas where only settlement is observed, there is only a moderate correlation between repair rate and vertical differential permanent ground deformation but the estimated model error is relatively small and so the model may be acceptable. In general, repair rates in the zone where no liquefaction occurred are very low and it is possible that repairs present in this area result from misclassification of hazard observations, either in the raw data or due -016-0077-3 to the approximations of the geospatial analysis. Along with hazard intensity, insulation material is identified as a critical factor influencing cable fragility, with paper-insulated lead covered armoured cables experiencing considerably higher repair rates than crosslinked polyethylene cables. The analysis shows no trend between cable age and repair rates and the differences in repair rates between conducting materials is shown not to be significant. In addition to repair rate functions, an example of a fragility curve suite for cables is presented, which may be more useful for analysis of network connectivity where cable functionality is of more interest than the number of repairs. These functions are one of the first to be produced for the prediction of damage to buried cables.123 Bull Earthquake Eng (2017) 15:3151-3181 DOI 10.1007/s10518

Towards a Decision Support Tool for Assessing, Managing and Mitigating Seismic Risk of Electric Power Networks

“…Principal causes of PGD [28] will be estimated in CIP-Cast-ES as follow: a) coseismic fault displacement in the near-fault area will be calculated via semi-empirical correlations as a function of the earthquake magnitude (e.g. the ones available from Petersen et al, 2011); b) landslides triggered by seismic shaking [29] -this capability will be included in CIPCast-ES as discussed in the Conclusion section of this paper); c) liquefaction, lateral spreading, and seismic settlement will be estimated in term of liquefaction potential index (LPI) that proved to be a good predictor for the damages induced on buried cables [30].…”

“…Repair rate relationship for buried cables. Kongar et al [30] produced for the first time evidence-based repair rates for the prediction of damage to buried cables, processing and analysing the damaged caused to them by 2010-2011 Canterbury, New Zealand, earthquake sequence. The analysis showed that the fragility of buried cables is influenced more by liquefaction than by ground shaking, and that lateral spread can cause more damage than settlement alone.…”

“…The analysis showed that the fragility of buried cables is influenced more by liquefaction than by ground shaking, and that lateral spread can cause more damage than settlement alone. Kongar et al [30] distinguished four different earthquake-induced geotechnical hazard zones (Table 4). Along with the typol-Towards a decision support tool for assessing, managing and mitigating seismic risk of electric power networks ogy of hazard and its intensity, the insulation material was identified as a critical factor influencing cable fragility.…”

Modeling Resilience in Electrical Distribution Networks

“…As far as adverse meteorological conditions are concerned, both the transmission and distribution systems have been adversely affected by water bomb causing flooding, extreme snowfall or windstorm, and overheating [1]. As an example, highvoltage overhead lines might be subjected to failure due to ice sleeves on conductors during snowfalls; medium-voltage overhead lines might be subjected to failure due to fall of trees during windstorms, while overheating can cause catastrophic failure of underground cables [4,5]. As an example, a clamorous case occurred in Auckland, New Zealand, in 1998 that involved the failure of four major underground cables due to overheating in the summer period.…”

Use of Variable Fuzzy Clustering to Quantify the Vulnerability of a Power Grid to Earthquake Damage

“…When scholars of different disciplines study the vulnerability of power grid nodes, they often analyze from their own professional perspective, and the research focus varies. Some literature is concerned with the response of mechanical properties of electric power facilities to seismic activity and the capacity of the facilities to resist structural damage [3][4][5]. Some literature describes the functional modeling of electrical substations as a method of studying how earthquakes damage these structures.…”