The Waverley West subdivision was announced in 2005 as a new 13,000-lot subdivision for the city of Winnipeg (Manitoba, Canada). It encompasses 2,600 acres (1,052 hectares) and, on completion in 18 to 30 years, is expected to support a population of 40,000 with 13,000 homes. Economic conditions created load forecast uncertainty, specifically whether the entire development would be completed quickly or in the more typical 30-year scenario. This uncertainty increased the risk of significant stranded assets as a result of the high probability of error between the anticipated and actual loads.

Manitoba Hydro's planners considered three options for the supply of this large subdivision. The first option, a traditional design, would have called for a new 100-MVA substation or two 60-MVA stations — each station requiring 3 acres to 5 acres (1.2 hectares to 2 hectares) of property — feeding 25-kV distribution feeders that supply the subdivision through single-phase, looped networks. The second option was the expansion of an existing station. The third option was to use high-voltage padmounted transformers (HVPTs) in multiple distribution supply centers (DSCs).

The last option would supply the proposed subdivision by installing 10 or 12 10-MVA, 66/24 kV DSCs, as loading required. Using this approach, it was expected the capital requirements for the life of this project would remain relatively low and flat.

Addressing Concerns

Subdivision developers had expressed concerns about how Manitoba Hydro was going to supply the new subdivision. They were especially concerned about the visual impacts of traditional substations. If the traditional station approach was to be used, then it was the subdivision developers' preference that it be placed underground or be moved outside the subdivision limits, in the countryside somewhere.

The idea of providing a 3-acre to 5-acre site for a new conventional station was rejected. In meetings with senior managers, the primary development companies insisted on an outright ban for a conventional station. They were adamant that whatever Manitoba Hydro installed should complement the subdivision surroundings and, with proper landscaping, be a seamless blend of natural beauty and modern living.

The solution was to use, in a new way, the Manitoba Hydro-developed HVPT in a DSC concept. With a 10-MVA capacity, it would require 10 to 12 sites interconnected on the perimeter of the subdivision. The minimal footprint of the DSC — typically measuring about 100 sq (9.3 sq m) with a low overall height of about 10 ft (3.1 m) — offered such a substantial aesthetic improvement over the traditional substation that, when developers of the subdivision were shown this option, they responded with an offer to provide 10 sites at no cost.

Flexibility Is Key

The flexibility offered by the DSC concept permitted the supply infrastructure to be staged to meet the progress of the subdivision development, with changing load profiles, rather than installing a complete traditional station, with redundant transformer capacity, and having to wait for 10 years to 30 years for the homes to be built and the load to materialize.

The second option was eventually ruled out because the existing station was too far from the subdivision to permit the installation of sufficient distribution feeders. While that approach was theoretically possible, it was practically impossible, given the limited right-of-way capacity. With everything considered, the DSC concept was expected to save between CDN$13.8 million and $14.6 million net present value (NPV) in capital infrastructure costs.

It must be noted the DSC scheme included a new distribution system, which called for an interconnected, automation-ready 25-kV three-phase network between DSC sites operated by S&C Electric's IntelliTeam smart grid system. Developers received service on time with enhanced aesthetics; the utility received a lower-cost installation; the customers received service with greater reliability. This was a true win-win-win.

Another real benefit is the use of the installed transformer capacity. In a traditional station, a redundant transformer is required at the outset and always resulting in 50% usage of installed transformer capacity for the life of the station. With the DSC concept, the spare transformation capacity is actually built into each part. The plan for phased capacity additions has the usage of the installed capacity ultimately rising to more than 90% while still providing a redundant transformer. For the same reason, a mobile substation and the provision of the connection itself is not required.