Lessons for the Fragility of Canadian Hydropower Components under Seismic Loading

This paper presents results from a seismic vulnerability analysis of the components of hydropower systems in Canada. A number of dams and their associated components (hydropower plants, switchyards, transmission towers, and supplementary equipment) at selected locations in western and eastern Canada were analyzed in the study. The seismic vulnerability for a given hydropower component was estimated by combining the probabilities of various levels of the seismic hazard at the component location, with the damage probabilities of the component corresponding to the seismic hazard levels considered. In this study, the seismic hazard was represented by the peak ground acceleration of the seismic motions. The calculation of the seismic hazard was based on the latest seismic hazard model developed by Geological Survey of Canada. The damage potential for the hydropower components was represented by fragility curves. The seismic vulnerability for each component was expressed by the damage probability as a function of peak ground acceleration. The results from this study show that the most vulnerable components of a hydropower system are the switchyards and the power plants. Introduction A hydropower system consists of a dam, reservoir, and electric power components, which include a power plant (turbines, generators and powerhouse), switchyards, transmission towers, and supplementary equipment, such as telecommunication systems. The purpose of the system is to transform water energy into electrical energy and to transmit that energy to consumers. The failure of a dam would often have serious consequences to people, community structures and the environment. In Canada the likelihood of such failures is reduced by application of the Dam Safety Guidelines (CDA 1999). However, damage to electric power components may also result in a significant disruption of power supply, which can cause large indirect economic losses. Shinozuka et al. (2000) reported that the direct costs of full restoration of the electric power system due to 1994 Northridge earthquake and 1995 Kobe earthquake were $500 million and $4 billion respectively; indirect costs are harder to quantify but are likely to be of a similar order. Obviously, failure of any component of a hydropower system will affect the serviceability of the entire system as well as perhaps the national power supply. The objective of this study is to investigate the vulnerability of hydropower components in Canada to earthquake excitations. Secondary earthquake-induced effects, such as landslides and tsunamis are not considered. The components considered in the study are the dam, power plant, switchyards and 1 Graduate Research Assistant, Dept. of Civil Engineering, University of Ottawa, Ottawa, ON K1N 6N5 2 Seismologist, Geological Survey of Canada, Natural Resources Canada, 7 Observatory Cres., Ottawa, ON K1A 0Y3