NEWS
JWinsulators
In early January 1998, a huge mass of moisture from the Gulf of Mexico met a stationary system of cold air from Labrador, resulting in sustained freezing rain and ice pellets over a vast area of southeastern Ontario, southwestern Québec and the northeast U.S. The onslaught lasted five days producing an accumulation of up to 80 mm of freezing rain and leading to what then became the largest power disruption ever recorded in North America. Millions were affected, some for weeks. Equally significant, the outage occurred during the harsh regional winter and in areas where up to 80 per cent of inhabitants rely on electricity for heating.
Most transmission towers used in Québec until that time were designed to bear up to 45 mm of radial ice – a load considered sufficiently conservative inasmuch as meteorologists claim that a situation of excess freezing rain occurs only once every 50 to 150 years. However, the combination of ice loading from the storm on these structures, which in some cases tripled their weight, and from ice-laden conductors brought down hundreds of transmission towers and tens of thousands of wood poles. In one unusual case, a 735 kV line built after 1973 survived the ice storm while a similar adjacent line built earlier was completely toppled. Although vertical capacity of the newer towers was probably less than for the older collapsed towers, balancing between components combined with anti-cascading structures managed to keep this line intact.
Most analysts of the Great Ice Storm of ‘98 agree that utilities must draw from the experience of such calamities to better prepare. For example, Hydro-Québec officials acknowledged that the utility did not have any computer simulation on how to respond to such a catastrophic power failure. While the severe freezing rain that lashed the region for days may have been without precedent in duration and intensity, these events could well become more common as the Earth experiences greater and greater climatic change.
