PROBABILISTIC-BASED HURRICANE RISK ASSESSMENT AND ...

1.1.4 Hurricane Risk for Power Distribution PolesThe power systems include three main components: the generation, the transmission, andthe distribution. The generation plants produce power and are generally large facilities,located in a centralized location. The transmission system transports large, city-sizedamounts of power long distances from the generation plant to the distribution substations.Transmission systems are comprised of lines that are approximately 150 ft high, strungbetween steel, lattice patterned towers that are 850 ft apart. The transmission lines carrypower at voltage level greater than 34.5 kV and the network is typically parallel (i.e. thereare two or more routes between two points for power to flow). The distribution systemtransports neighborhood-sized amounts of power several miles to individual customers.The distribution system includes lines that are 30 to 50 ft high, strung on timber poles,located 100 to 200 ft apart. The power carried by the distribution lines is at 34.5 kV orlower voltage levels, and the network is radial (i.e. one route between two points forpower to flow) (Saadat 2002). Figure 1.2 shows a generalized schematic of the powersystem.The vulnerability of these three components to potential damage due to hurricane windsvaries. As generation plants are few in number and are often designed to withstand highwind speeds, damage to the plants is rare. Damage to the transmission system is also rarebecause these lines and towers are designed to withstand high wind intensities, and theyusually have large tree setbacks. The parallel network of the transmission lines alsoinsures against lengthy or costly loss of power supply to communities (Davidson et al.2003a). The distribution systems (lines and poles), on the other hand, are the mostsusceptible to damage due to high wind intensities. This is mainly because moredistribution lines and poles are exposed to hurricane winds than transmission systems, thedistribution poles are not often designed to withstand high wind speeds (Davidson et al.2003a).20