Vulnerability of electricity supply under extreme weather conditions



Extreme weather conditions can dramatically impact the electric power system. For instance, the “Lothar” hurricane in 1999 provoked power disruptions in several European countries for days. The strong wind brought down kilometers of EHV overhead power lines (OPL) on a large scale. Power lines are devised to withstand the vast majority of the weather conditions they can encounter. In case of extreme and infrequent Extreme Weather Event (EWE), outages are unfortunately inevitable. For economical reasons, OPL cannot be designed to resist to any force of the nature of any strength. Other factors can affect the OPL reliability like their standard of construction, lack of correct maintenance, proximity of vegetation, …

OPL failures during EWE’s are unavoidable but their frequency and their consequences on the power supply can be reduced. EWE’s are likely to cause Common Mode Failures (CMF) which can strongly endanger the security of supply. The identification of plausible and critical CMF can help to secure the supply. Plausibility of failures is hard to obtain in proportion to the lack of reliable data regarding EWE’s. Indeed, they are infrequent with a great time-space variance that makes hard to calculate accurate probabilities of (common) failures. A relative index of plausibility has been chosen to rank CMF according to our model. Criticality is obtained by a contingency analysis performed with load flows of some particular and representative scenarios of the power system to study (CH in our case). CMF that create overloads or trigger cascading failures are identified and ranked on a scale of criticality. In order to identify these plausible and critical CMF, a methodology has been developed and implemented using Geographic Information System (GIS), contingency analysis of electrical network (Neplan) and Matlab.

A Matlab-based application has been created to simulate EWE and determine the vulnerability of the security of supply. Although this application is still under implementation, the preliminary results are encouraging. Thunderstorms have been simulated based on a 10 years lightning strikes data base of Switzerland. More than 1400 periods have been retained to calculate the CMF plausibility for 2 summer scenarios of the Swiss transmission network. Some tools as been developed to show the exposure of any OPL section, exposure correlation between sections or OPL, total exposure of any sections,… The application is flexible and let us easily integrates new tools. Other EWE like hurricane or wet snow accretion could be simulated in the future.



Identification of plausible and critical common mode failures provoked by extreme weather conditions

Identification of possible countermeasures to handle and reduce the vulnerability of the security of supply

Test the efficiency of the countermeasures and evaluate their feasibility

Conception of a flexible application for weather and power system simulations and analyses 




Here under a general view of the methodology:




A)     Extreme weather events simulation: Past weather data, spatial interpolation, Geographic Information System (GIS), OPL path, topography and vegetation, exposure and failure plausibility calculation, plausible contingencies generation

B)     Power system model for AC-flow, electrical scenarios , European transmission network, upcoming transmission and generation infrastructures, power flow transit

C)     Contingency analysis, Neplan, cascading failures & hidden failures, identification of plausible and critical contingencies

D)     Vulnerable lines and sections, suggestion of efficient measures as local reinforcements, modifications of topology, construction of new OPL

Here are some preliminary outcomes that show the potential of the methodology: