MRO Magazine

Main Electrical Substation Upgrades

Part 2 – Project Phasing, Construction and Commissioning

January 21, 2021 | By Philip Chow and Bavan Poologarajah

Civil work for the temporary substation is being completed in the background. Sunnybrook remained powered from its existing substation in the foreground. Photos: Philip Chow

Civil work for the temporary substation is being completed in the background. Sunnybrook remained powered from its existing substation in the foreground. Photos: Philip Chow

In part one (February 2020 issue) we discussed design considerations, planning and equipment selection decisions for upgrading the main outdoor electrical substation at Sunnybrook Health Sciences Centre. With an equipment package consisting of 38 kV class gas-insulated switchgear housed in customized E-Houses, four new 7.5/10 MVA KNAN/KNAF transformers, and an intelligent control and monitoring system pre-selected, the next challenge was developing a detailed project phasing strategy, which coordinated utility upgrades to the site, demolition and construction of a new substation, while maintaining a reliable power distribution system to the site, and implementing the phasing strategy over a two and half year construction schedule.
“Sunnybrook’s main outdoor electrical substation is critical in providing reliable power throughout the entire campus,” said Michael McRitchie, Director of Plant Operations, Maintenance and Biomedical Engineering, Sunnybrook. “Minimizing power interruptions during construction was a key priority for the team.”

The temporary substation is nearly complete, with equipment landed and 5 kV feeders being installed to the hospital’s main 4.16kV distribution switchgear. Photo: Philip Chow

At the onset of the project, coordination with the local electrical utility was an essential part of the planning process. Not only would Sunnybrook’s new main outdoor electrical substation provide critical power throughout the hospital, but it would interface with Toronto Hydro’s distribution system, which supplies power to the City of Toronto. Coordination on various design features, operational aspects and construction work was essential to ensuring a successful outcome.
Frequent design, planning and construction meetings were held between the utility, project engineers and hospital staff, throughout the project. In addition to replacing end of life equipment at Sunnybrook’s existing substation, the project would incorporate a new utility circuit from the local transmission station to site, replacement of existing utility feeders on the Sunnybrook campus and the installation of new SCADA controlled pad-mounted switchgear in the substation. A detailed phasing plan, with 14 major phases of construction was developed by the project engineers, which allowed both the project contractor and electrical utility to complete the work required to build the new substation, and connect it to an upgraded electrical service, while minimizing disruption to a fully operational hospital.
With a pre-selected equipment package and detailed phasing plan in place, the project was tendered to a group of pre-qualified electrical contractors, and awarded to Ontario Electrical Construction Company Ltd. Construction on the project started immediately after the project was awarded. First phase of the project involved constructing a temporary substation, which would allow for Sunnybrook’s existing substation to be decommissioned and demolished. Given the various construction parties involved with the work, including the hospital contractor, utility, and utility contractor, the project engineers needed to take a hand’s on project management approach to coordinate work between the various parties, and chaired numerous construction meetings over the course of the project.
When the civil work was complete for the temporary substation, newly manufactured equipment (for the permanent substation) was installed in the temporary substation, and one of the incoming 27.6 kV utility circuits was routed to it. The temporary substation and temporary utility feed had to be strategically located, such that they would not be affected by future demolition work, and future construction of the permanent substation. While the temporary substation was being commissioned and subsequently energized from one utility circuit, the hospital remained supported by the second utility circuit, thereby avoiding any utility power interruptions associated with temporary construction.

Once Sunnybrook was supported from the temporary substation, the existing substation was demolished and civil work for the new permanent substation started. Photo: Philip Chow

Once the newly constructed temporary substation was energized, each of the four new 7.5 MVA transformers were connected to part of Sunnybrook’s 4.16 kV distribution network, until the entire hospital was powered from the temporary substation. The cutover process was completed over four weekends, minimizing power interruptions to parts of the hospital during each cutover. Demolition of the existing substation started immediately after the last cutover was completed. Existing overhead distribution and pole mounted switches were removed by the electrical utility and existing switchgear and transformers were removed by the project contractor.
Civil work on the new permanent substation followed demolition work, with excavation and foundation work for a network of below grade service trenches. The new gas-insulated switchgear only accepts incoming and outgoing feeds via bottom entry connections, so below grade cable chambers and service trenches were required to connect the new upstream load break switches, and new downstream power transformers to the GIS.
Important design parameters were incorporated into the below grade service spaces, including: need for multiple access points; ability to house multiple levels of cable tray, and associated support structure, that facilitates future installation of new 27.6 kV campus circuits; maintaining cable bending radii for connections to equipment; concrete sloping and drainage, ensuring water penetration into the space would be routed to a sump pit and pumped away to the site’s drainage system.
When the civil work for the new permanent substation was complete, the load-break switch and E-House with integral GIS line-up, which were not in use, were installed in their permanent location. The incoming utility circuit, not in use during construction of the permanent substation, was connected to the switch, and the second gas insulated switchgear line-up was energized.

When civil work was finished in the new permanent substation, equipment was craned into place and energized in a phased approach. Both the temporary substation and permanent substation were operational for a period of time, to minimize disruption to the hospital. Photo: Philip Chow.

As initial electrical connections were being completed in the new permanent substation, the entire hospital remained supported from the temporary substation. Given the increased capacity of the new transformers, the hospital’s load could be fully supported off of three of the new transformers, while maintaining an N+1 redundancy in available capacity to support the electrical load. One of the four transformers was disconnected from the temporary substation, craned to the permanent substation, connected and energized. Once this transformer was online and serving hospital load, the process was repeated until three transformers were relocated to the permanent substation, and Sunnybrook’s entire load was being supplied from the permanent substation, in a temporary configuration.
At this point, the remaining equipment (the second E-House, a load-break switch, and the fourth transformer) in the temporary substation was relocated to its permanent position. The second utility circuit was connected to the second line-up of GIS, and two of the four transformers were subsequently connected. A tie connection between the two line-ups of GIS was installed, along with control/alarm wiring interconnections, and redundant pathways for the controls network. As the remaining electrical installation was being completed, the foundations for the temporary substation were being demolished and the parking lot was remediated.

Once the new permanent substation was operational (foreground), the temporary substation was demolished and the parking lot was remediated and returned to use. Photo: Philip Chow.

Throughout the project, a detailed commissioning plan was developed by the project engineers to test equipment, both in temporary and in permanent configurations. A test script was created for all of the new equipment, and commissioning was split in two groups: standalone tests and dynamic tests.
Standalone testing included: site acceptance tests for cable insulation and transformers; detailed site verification of protective relays, with functional verification of differential protection systems, for gas-insulated switchgear and transformers; and monitoring and control systems, including the transformer dissolved gas analysis (DGA) monitoring systems, which were networked to Sunnybrook’s alarming and data logging server.
Field service representatives from the various equipment suppliers would often have to be on-site at the same time, for joint commissioning efforts, which required additional coordination efforts. Once standalone testing was completed, final dynamic testing of the new automatic transfer system for incoming 27.6 kV utility circuits was scheduled with the hospital and utility. Various scenarios of utility power outages, including single circuit outages and coincident outages of both incoming circuits, were tested by opening and closing main load-break switches in the substation.

The gas-insulated switchgear (left photo) and 27.6 kV automatic transfer system (right photo) were dynamically tested at the end of the project. Photos: Philip Chow.

With the 27.6 kV automatic transfer system fully commissioned, Sunnybrook was left with the ability to transfer between utility circuits, in the event of a prolonged utility outage. One of the main challenges during the commissioning period was the onset of the COVID-19 pandemic, before the final dynamic tests were scheduled to occur in April 2020. Recognizing the importance of having the new substation fully commissioned, Sunnybrook undertook a significant effort to organize internal services to ensure disruptions associated with testing were minimized. Additional precautions were taken by the parties on-site, such as daily screenings before entering the job site, maintaining two-metre social distancing, wearing masks on-site, and minimizing the number of people in enclosed spaces, during testing.

Photos: Philip Chow

Replacing a main outdoor electrical substation can seem like a formidable challenge. By developing a detailed design, a phasing strategy, which minimized the impacts of construction, and maintaining a coordinated approach to construction management, Sunnybrook Health Sciences successfully upgraded their substation.
Similar to the equipment selection process, a number of innovative features were incorporated into constructing the new permanent substation. Removable, composite panels were used throughout the substation, to provide access to below grade service trenches and cable chambers, for the installation of future circuits. Medium voltage armoured cables were used as feeders and colour-coded based on voltage class, to help distinguish 5 kV and 35 kV circuits. Free-standing, fire rated walls were installed between transformers to provide an improved level of protection, in the event of an unexpected transformer failure. New fencing, flood lighting, and security cameras were installed, along with a ground grid spanning the entire substation area and complete with ground rod inspection boxes, for future maintenance and testing.
“The project was a success,” said McRitchie. “Sunnybrook will have an intelligent substation that will support future campus development and power the hospital’s distribution network for many years to come.” MRO
Philip Chow, P.Eng., P.E., was the lead engineer on the project and is a senior project manager at H.H. Angus & Associates Ltd. He specializes in electrical projects and construction in critical facilities and can be reached at
Bavan Poologarajah, P.Eng., was the senior electrical designer on the project. He has worked on a number of electrical projects in critical facilities and can be reached at


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