Main Electrical Substation Upgrades
March 23, 2020
BY Philip Chow and Bavan Poologarajah
Design Considerations, Planning, and Equipment Selection.
Institutional campuses and large facilities share a common design feature: the use of a main outdoor electrical substation, used to distribute power to buildings and site loads across a large area. With an electrical demand load (kW or kVA), typically proportional to the size of the facility, campuses are often supplied by one or more electrical utility circuits at a supply voltage of 15kV or higher, due to circuit loading and ampacity constraints.
Incoming utility circuits are routed to a main outdoor electrical substation, which serves as the demarcation point between utility infrastructure and customer-owned electrical infrastructure. From here, the incoming utility service is distributed within the campus either at the service voltage or at a lower voltage, through the use of step-down transformers. A main electrical substation is a major component in an infrastructure portfolio and facility managers often face the problem of how to upgrade end-of-life equipment, without impacting operations.
Sunnybrook Health Sciences Centre (Sunnybrook) faced these challenges when it undertook a project to upgrade its main outdoor electrical substation. In this, the first of a twopart series on electrical substation upgrades, we will look at design, planning, equipment co-ordination, and procurement associated with this project.
Sunnybrook is a full-service, 1,355-patient bed hospital, with an aggregate campus area of approximately three million square feet. It is the largest regional trauma centre in Canada and has 1.3 million patient visits each year. At the onset of the project, Sunnybrook received its electrical service via two incoming 27,600V utility circuits. The existing outdoor substation consisted of 27.6kV load-break, switch and fuse type, switchgear, and four oil-filled power transformers, rated at 5/6.66 MVA ONAN/ONAF, which supplied a 5kV distribution network and approximately 20 smaller, downstream building substations.
Equipment in the existing substation had been installed over time, as campus development occurred, with the oldest sections of the existing switchgear lineup and power transformers dating to the 1970s. Routine preventative maintenance identified a number of issues with older equipment, including high dissolved gas levels in two of the power transformers (condition three and condition four dissolved gas levels), signs of corona damage on a high voltage bushing, and corrosion in the existing switchgear.
With equipment reaching end-of-life conditions and the future reliable operation of equipment being questioned, Sunnybrook undertook a project to upgrade its substation.
“Sunnybrook’s main outdoor electrical substation plays an essential role in distributing power throughout the campus,” said Michael McRitchie, Director of Plant Operations, Maintenance and Biomedical Engineering, Sunnybrook. “To ensure our substation would meet future campus needs, a project that completely upgraded the existing installation was prioritized.”
Given the large capital expenditure associated with building a new substation, an analysis of project goals and constraints was performed.
Project Design Goals Included:
• Increasing capacity within the new substation for future campus development;
• Allowing for the connection of a future combined heat and power plant and a future battery energy storage project;
• Developing a smart substation that would allow for improved monitoring and control features; and
• Improving on an existing automatic transfer system, which allows hospital staff to transfer between incoming utility feeders.
Project constraints included building within the footprint of the existing substation; creating a project schedule that aligns with funding requirements; minimizing any parking space losses in adjacent parking lots; and minimizing the impact of construction-related power interruptions to the hospital.
Project work would have to be carefully co-ordinated with work by Toronto Hydro, which included transitioning Sunnybrook from an overhead utility circuit to an underground utility circuit, replacing several kilometres of underground duct banks and utility cables for future capacity; and, to help facilitate construction of the new substation, replacing existing overhead switches with pad-mounted switchgear and upgrading utility metering and SCADA connections.
Design of Sunnybrook’s Main Outdoor Electrical Substation Redevelopment project commenced with the development of several concepts for a replacement substation. The first major design challenge was selecting the new service entrance switchgear. With a requirement for future generation sources to be connected in parallel with the utility, associated utility grade protection, metering and control features, and the ability to automatically add and disconnect loads, it was clear simple switch and fuse type switchgear would not be sufficient for future needs. Vacuum circuit breakers and switchgear with customizable metering, protection, and control elements would be required.
Using traditional, air-insulated switchgear in a weatherproof enclosure was initially considered; however, the footprint of the proposed lineup would necessitate a substantial expansion of the substation area and the loss of adjacent parking spaces. Consequently, the use of sulphur hexafluoride (SF6) insulated switchgear, also known as gas-insulated switchgear (or GIS), was considered. Given the high dielectric strength of SF6, GIS provides a more compact installation, with a footprint that is approximately 50 per cent of the size of equivalent air-insulated switchgear.
While gas-insulated switchgear is available in varying configurations, traditional freestanding type switchgear was selected as the right option for the project, given its ability for customization and improved ease of operability. Using panel type gas-insulated switchgear would require an indoor environment. As the funding constraints for the project prohibited the construction of new occupiable space, prefabricated enclosures for the electrical equipment (E-Houses), with a conditioned environment, would need to be supplied along with the GIS.
The next design challenges included creating additional capacity in the electrical substation for future campus development and designing a control system that would provide automated control of the gas-insulated switchgear. A load study for the site was performed, and forecasted load growth was contrasted with site constraints, which included both physical spaces to build on and electrical constraints in the existing electrical distribution system. It was determined that the existing 5MVA transformers could be replaced with four new 7.5/10 MVA KNAN/KNAF transformers, increasing the aggregate capacity of the new substation by a factor of 1.5 on the base rating (30MVA).
Completely replacing the existing transformers would also provide an opportunity to incorporate several innovative design features, including on-board dissolved gas analysis monitoring, alarm integration with the substation’s TCP/IP based control system, and improved transformer protection features with new protective relays. To improve power system reliability, an automatic transfer system was included to provide the ability to automatically switch between the two incoming utility circuits, in the event of an outage on a utility circuit.
Additional features included load management of 27.6kV feeder; user-friendly HMI screens with metering, alarm, and control features; and full hot/standby capability with redundant PLCs and system components. To integrate with the existing alarm and control system for the campus emergency generators, an Allen Bradley ControlLogix platform was used.
With major equipment concepts finalized, detailed engineered drawings and specifications were created for equipment procurement packages. Given the integrated requirements between the gas-insulated switchgear, its associated control system, and the E-House enclosures, one consolidated equipment procurement package was developed for GIS suppliers. A second independent procurement package was developed for the four 7.5/10 MVA liquid-filled power transformers.
Equipment suppliers submitted proposals for the separate packages and submissions were evaluated through a detailed RFP process, which reviewed bid compliance, company capabilities, production schedule, price, and other factors. The gas-insulated switchgear package was awarded to Siemens Canada, with Toromont CAT as the control system sub-supplier and AMSi Inc. as the E-House sub-supplier. The power transformer package was awarded to Northern Transformer Corp. Suppliers were directed to proceed with detailed design for equipment shop drawings, while the engineered design for the construction package was finalized.
“Pre-selecting major equipment provides an excellent opportunity for the owner to have direct input into the procurement process and to advance the project schedule,” said McRitchie. “Developing equipment procurement packages, selecting suppliers, and having detailed equipment shop drawings produced, prior to construction, allowed the construction team to focus on delivery and installation.”
As the pre-selected equipment would be critical to the successful operation of Sunnybrook’s new substation, a rigorous quality assurance program was maintained throughout manufacturing. The 38kV class gas-insulated switchgear underwent in-depth acceptance testing at the Siemens factory in Germany, with both the project engineer and hospital representatives attending.
Tests included a detailed inspection of components, mechanical and electrical operation tests, dielectric tests, verification of interlocks, and SF6 gas measurement tests. Once initial factory witness tests were successfully completed, the GIS was cleared for shipment to Canada. Several months later, the switchgear sections were installed in two separate E-House assemblies, complete with automatic transfer system (ATS) control cabinets. The E-House assemblies were equipped with a multitude of custom features, specified by the project engineers, including redundant HVAC systems, redundant DC power systems for station power, clean agent fire suppression systems, and specific criteria for construction of the enclosures and finishes.
An integrated acceptance test was subsequently performed, which tested the functional operation of the switchgear’s ATS, through the custom control system and HMIs, and tests of the various systems in the E-Houses and protective relays in the switchgear. Concurrently, the new power transformers were prepared for in-depth acceptance testing at the high voltage test lab at Northern Transformer’s factory. Transformer acceptance testing included a detailed physical inspection, heat run tests, electrical tests, dissolved gas analysis monitor tests, and lighting impulse (BIL) tests. Once the new substation equipment successfully passed all of the required off-site testing, it was cleared for shipment to the site.
Upgrading critical electrical infrastructure in a campus’ main outdoor electrical substation can require significant upfront planning. Decisions on equipment technologies, capacities for future load growth, and opportunities for functional improvements, both for operation and maintenance, need to be made before proceeding with the detailed design for construction drawings and specifications.
Given the complexity associated with procuring integrated equipment packages, and the desire to have technical and functional merits included in the bid evaluation process, it can be advantageous to have the owner and their engineer manage equipment procurement.
In the second part of the series on substation upgrades, we’ll examine the multi-phased construction project that allowed Sunnybrook to completely upgrade its main outdoor electrical substation, while minimizing power interruptions to the campus. 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 firstname.lastname@example.org.
Bavan Poologarajah, EIT, 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 email@example.com.