An updated solution3 June 2003
Jean-Maurice Bouchard and Gilles Lafleur explain how two gantry cranes are playing an integral role in rehabilitation work at Beauharnois generating station in Canada
AS THE GOVERNMENT of Québec power generation and distribution Company, Hydro-Québec continuously looks into ways of maintaining and improving the supply of electricity to its various markets. The commissioning of new power houses is obviously a means of achieving this aim; but as the water streams to harness become scarce and further away and the existing installations reach their economic lives, rehabilitation becomes a viable solution.
Because of its large capacity and useful location, Beauharnois generating station plays a strategic role in Hydro-Québec's power system. It supplies not only a portion of local and regional demand but also demand from neighbouring systems in Ontario and the US, on certain occasions.
The generating station fills three strategic functions:
• To meet electricity demand.
• To quickly restore power to Greater Montréal in the event of a system-wide outage.
• To sell electricity to neighbouring systems in Ontario and New York State.
It is imperative for Hydro-Québec to make sure that the Beauharnois development continues to fill these three roles under optimum conditions. Major rehabilitation work had become necessary in Beauharnois since the concrete structures were aging and some of the equipment was outdated.
Before coming to a decision, Hydro-Québec conducted a comprehensive draft-design study in 1988-89 in order to determine the best course of action. This approach was chosen since it covered all of the options available to the utility in such a case, including reconstruction or decommissioning of the generating station. The general aim is to maintain the facilities in good operating condition and ensure that maximum capacity is available at the lowest possible cost.
The study showed that it would be cheaper to modernise the existing generating station than build a new one. In addition to being the least costly solution, rehabilitation is in line with Hydro-Québec's strategic objectives, which are to keep rated in check and maintain the quality of service in Québec while ensuring corporate growth.
The rehabilitation of Beauharnois generating station has now been under way since the end of 1994.
Spread out over roughly 15 years, the renovation and modernisation work is designed to make the infrastructure last 50 years longer and the electrical and mechanical equipment 25 to 40 years longer. It will also bring the station up to today's standards, keep it in operation, and improve its reliability.
The US$1.03B project will increase the generating station's installed capacity to 1673MW.
Beauharnois generating station is situated 40km southwest of Montréal, Canada, between two lakes, Saint-François and Saint-Louis, in the municipality of Melocheville. Until Robert Bourassa generating station (formerly La Grande-2) came into service in 1979, it was the most powerful station in Hydro-Québec's system.
Today, with an installed capacity of 1673MW, Beauharnois ranks fifth among Hydro-Québec's power plants, but second in terms of energy output.
It would take from 1902, when Beauharnois Light, Heat and Power Company was founded, until October of 1929, when the groundbreaking ceremony was held, for Beauharnois generating station to go from dream to reality. Since the turn of the century, Joseph Robert and his family had been convinced of the site's tremendous hydroelectric potential. They owned a small canal that fed into the Saint-Louis river and envisioned a powerful run-of-river generating station on it. But the project would not begin to take shape until late in the 1920s, when the renowned engineer Robert Olivier Sweezy arrived on the scene.
Beauharnois, built in three phases, is the largest hydroelectric generating station powered by the waters of the St. Lawrence river.
The first 14 generating units, with a total capacity of 538MW, were placed in service from 1932 to 1948. The peak of construction saw 2300 workers on the site, with 500 of them living in camps nearby.
Hydro-Québec built the second section of the power house from 1948 to 1953, adding 12 new generating units with an installed capacity of 483MW. At that point, Beauharnois generating station ranked second in North America. Phase three of construction, which ended in 1961, added 10 more generating units and raised the installed capacity to 1574MW. Coincidentally, the generating station was finished just as the nationalisation of Québec's electricity industry was completed in 1963.
Today the generating station's facilities are still impressive: it has 36 generating units, as well as two small units, set out side by side in a building that extends almost 1km over the Beauharnois canal.
The rehabilitation project
The main challenge in the rehabilitation project is to keep the generating station in operation, since it has to continue supplying power to the grid. The strategy that was retained consists in dividing the work into three blocks, each with a different time frame.
With the exception of the first block, which also included the construction of a new 120kV substation, the type of work is the same in all three blocks, although each one involves a different group of generating units.
Hydro-Québec has succeeded so far in carrying out the rehabilitation work with minimal disruption to the power station operations. For instance, major repair work did not prevent the station from generating 12,740GWh of energy in 1997, breaking the record of 12,400GWh attained in 1973 before the project began.
Within the segment of modernisation of the equipment, canadian-overhead-handling (COH) a Boisbriand, Canada based company, dedicated since 1969 to the fabrication of Custom Design cranes and hoisting machineries, was awarded a US$4.8M turnkey project for the supply of two 136t, Stalled Torque Duty, Gantry Cranes installed and commissioned by experienced crew.
The first gantry was successfully commissioned in October 2002 and the second one, presently under construction at COH facility, will be commissioned by October 2003.
The main duties of the gantries include the service of the water intake gates and screens, handling of the hydraulic trash grab and clam shell mud bucket and finally the hoisting of the departure transformers from the ground level to the dam deck 92 inches up.
Serving a dam of this magnitude in Quebec's extreme weather where temperature ranges from 40°C in the summer to 40°C (and sometimes worse) in the winter, the existing gantries were due for replacement.
SNC-Lavalin consulting engineering firm worked closely with Hydro-Québec engineers to develop specifications encompassing all required duties of the equipment and assuring that the most up-to-date technology would be utilised, projecting the overhead handling tasks in the 21st century.
The gantry hoist house, sitting at 60 inches above the dam deck, shelters a twin hook 136t main hoisting machinery and two separate fast speed, open winch type, 3t secondary general purpose hoists.
Below the hoist house, straddled in between the two main hooks, a 25t auxiliary trolley rolls on a separate set of girders allowing the hook to cantilever 4m past the upstream gantry travelling rail to perform the cleaning duties.
All the above hoists are designed and fabricated by COH. All the gearboxes for the open winch hoists, trolley and gantry travel drives are of COH's own design and fabrication.
All the machineries are run with Marathon motors controlled by ABB ACC601 hoist and ACS601 horizontal translation AC Variable Frequency Drives.
Advantages of the gantries include:
• The 150% stalling torque capacity of the main and auxiliary hoists are electronically controlled.
• A Modicon PLC system, configured and programmed by COH software engineers, controls a vast array of functions and interlocks helping the operator maximise the safety of the operation.
• The PLC is coupled to I/O modules connected to each other by a network of Optic Fibre reducing drastically the interconnection wiring in between the modules and main panel, but also between the back plates in the main panel itself.
The operators have the benefits of a spacious, totally enclosed, air-conditioned and heated cab allowing them to better master their working environment. The cab offers an outstanding window arrangement allowing close to 360° visibility in both the vertical and horizontal axis facilitating ease of operation and thus safety.
The operators swivelling chair is fitted with armrest type consoles housing all motion feather control joysticks, switches, alarm and pilot lamps. An LCD intelligent display also allows the operator to communicate with the on-board PLC, keeping him all the time abreast of the condition of the equipment.
Related ArticlesSpotlight on… Canada