There are only a few installations worldwide whose purpose is to assess performance of different designs of line hardware and conductors under stresses caused by environmental factors such as wind and icing. One of these, operated by Hydro-Québec, is located in a flat agricultural region south of Montreal.
In 2017, INMR visited this installation and also the related conductor and hardware test facility at the nearby Institut de recherche (IREQ).
Hydro-Québec’s transmission system consists of over 34,000 km of lines of which about a third operate at 735/765 kV. Indeed, this was the first network in the world to rely so extensively on 735 kV lines to link hydroelectric power in the province’s distant northeast with key demand centers in Montréal and Québec City.
Given the vast scale of this power grid and the typically severe wintry conditions to which it is exposed, testing different conductors and related line hardware such as dampers and spacers has always been a priority. In the past, this work was performed at a facility located on the windy Magdalen Islands at the mouth of the St. Lawrence River. Then, in 1991, testing was relocated to a special line in Varennes, only minutes from Hydro-Québec’s major research and testing institute.
Pierre Van Dyke, a Sr. Scientist in the group charged with such testing and also active in the related CIGRE Working Group within SC 22 (Overhead Lines), explains that the 1.575 km test line consists of five spans – three suspension and two dead-end.
Distances between suspension towers vary from 400 m to 450 m, the latter being the average length of the spans used on the Hydro-Québec transmission network. Van Dyke also points out that the test line has been refurbished twice over the years with all the former gauges replaced by a new data acquisition system as well as centralized computer control.
The basis for selecting four suspension towers was to reproduce a typical line section with three suspension spans, where most conductor problems such as strand failure from fretting tend to occur. This is also where dampers and spacers play a critical role in minimizing such damage. Says Van Dyke, “spacers and spacer dampers not only maintain the geometry of conductor bundles under normal service conditions but the use of unequal subspan lengths (distances between spacers or spacer dampers) will reduce the susceptibility to subspan oscillations. Spacer dampers also dampen Aeolian vibrations by allowing the energy to be dissipated.”
Van Dyke explains that three anemometers positioned on poles along the middle span monitor the wind speeds that actually impact conductors and line hardware. The horizontal wind flow will generate vertical aeolian vibrations due to alternate shedding of vortices from the top and bottom sides of the conductor. The test line site is also equipped with a full-fledged weather station that records not only wind velocity, azimuth and turbulence but also meteorological variables including barometric pressure and air density. Such information is then readily available depending on the data needs of any particular research project.
Our facility is unique in the world,” reports Van Dyke. “Although there are test sites in Japan devoted to study of galloping, here we are able to also work on other phenomena, from Aeolian vibrations to low frequency sub-span oscillations that lead to conductor clashing. Such oscillations not only risk damaging conductor strands but also impact articulation of the spacer dampers.”