New underground transformer station in downtown Toronto designed to withstand floods

With condominiums sprouting up in Toronto’s downtown core and along the lakeshore, Toronto Hydro is having to build a new transformer station to ensure it can fulfill the area’s energy needs. Since 2006 the population of down has increased by over 50%, compared to a growth of 9% in the city as a whole. Even though the downtown area already has five transformer stations, Toronto Hydro believes that between 2017 and 2022 the load demands will be more than they can handle.

As a result excavations are under way to construct the new Copeland 144-MVA transformer station in Roundhouse Park near the Metro Toronto Convention Centre and CN Tower. The park site has train locomotives and other railway artefacts, as well as the massive roundhouse and turntable where trains were once repaired. The roundhouse now houses a brewery, store and other amenities.

The transformer station is being built mostly below the reconstructed machine shop at the side of the roundhouse. The shop has been temporarily disassembled brick by brick and will be reassembled around 2014 to house the transformer station’s controls and protection equipment. The main equipment such as the transformers, switchgear and cabling will be located below in three underground levels excavated to 45 feet below grade. The electrical supply will come via a new underground cable tunnel from existing 115-kV circuits within Hydro One’s Front Street tunnel.

IBI Group is the consulting engineer for the station, and MMM Group is consultant for the cable tunnel.

The station is being built below ground to minimize the area it takes up and to help it blend in with the surroundings, but after floods knocked out two transformer stations in Toronto’s west end in July, questions have been raised about the wisdom of burying the station underground.

Toronto Hydro’s spokesperson, Jennifer Link, points in an e-mail out that the sensitive control and protection equipment is located above grade. And the underground structure is being carefully designed to withstand flooding: “A caisson wall is being constructed for shoring. Approximately 400 [concrete caissons] will be installed, interlocking to form the basis of the wall surrounding the station. The station walls will rest within the caisson wall, which will be relatively impermeable. The station exterior (walls, floor and roof) will be concrete containing a waterproofing admixture and completely enclosed in a waterproofing membrane. There are no penetrations in the foundation that will allow water entry.”

Also she writes: “There are three sump pits with redundant sump pumps fed from redundant power supplies and emergency transfer switches. Three sources of power are incorporated into the station services design and there is provision for additional emergency power connections.”

The $195-million project is currently on schedule, with excavation well under way

An on-site construction camera can be viewed here.