Of the Substations that ITCTransmission Initially Acquired in 2003, four were mid-1970s vintage gas-insulated substations (GIS). The SF₆ gas used as the primary insulating medium for the 120-kV transmission bus and circuit breakers had been leaking since just a few years after the original installation. The gradually increasing rates of SF₆ gas emissions from the GIS bus and the problematic dual-pressure gas circuit breakers had been a black eye against the overall performance and expectations of the small-footprint GIS that were installed.

ITCTransmission, a subdivision of ITC Holdings Corp. (Novi, Michigan, U.S.), had one substation in particular, the St. Antoine site, that had developed numerous breaches, which resulted in weekly service call-outs to raise the pressures back to the normal level. When these problems began occurring, the gas leaks were not considered an environmental issue; rather, they were viewed as helping to contribute to a service man's job security and paycheck. After several attempts to repair the variety of leak sources and welded bus construction (with limited success), it simply became routine to either react to frequent alarms or schedule gas fills.

The St. Antoine site was not alone in being problematic. The three other sites within a 10-mile (16-km) perimeter feeding into the city of Detroit, Michigan, presented nearly similar challenges during the course of their lifetimes. In retrospect, the empirical evidence suggests the OEM designs of the 1970s era were not robust enough for the outdoor environment and seasonal climate changes of Michigan. The four existing GIS sites did not have the advantage of being housed in the climate-controlled indoor environment that other utilities with GIS decided was prudent.

Because the four GIS sites were located in Detroit and fed important loads, including General Motors' world headquarters, a reliable transmission supply throughout the city was deemed an important issue, as was heightened international awareness of greenhouse emissions affecting climate.

To a lesser degree, but still important, was that there were very few critical spare parts for the 30-year-old GIS equipment. The substation designs had been out of production for a long time, and in the event of a serious failure, ABB (Zurich, Switzerland) and AREVA T&D (Philadelphia, Pennsylvania, U.S.) anticipated long lead times in support of the OEM equipment. Quite simply, given the frequent maintenance of the vintage GIS, their effective life cycle had ended.

So, by early 2004, the ITCTransmission engineering group took steps to address the 120-kV GIS infrastructure issues at the St. Antoine, Caniff, Midtown and Cato substations.

AN ALLIANCE PARTNERSHIP

Implementing a business strategy, ITC Holdings Corp. — including its subdivision ITCTransmission — entered into an alliance partnership with Mitsubishi Electric Power Products Inc. (MEPPI; Warrendale, Pennsylvania). Although there is nothing revolutionary about the company's tight manufacturing tolerances, simple proven designs and attention to detail during assembly (especially with single O-ring seals and sealant products), MEPPI has developed a reputation for high-quality products with the lowest overall cost of ownership.

Choosing to partner with MEPPI made sense to ITC for a variety of reasons. An important design feature required for new circuit breakers was that the mechanisms driving the interrupters not rely on pneumatic or hydraulic pressure. ITC's past experience with the inherited air-blast and hydraulically driven circuit breakers was that these systems required frequent maintenance and repairs. Also, earlier versions of gas breakers and other equipment using SF₆ had a less-than-stellar record of being leak-free, producing moisture ingress and refilling problems. MEPPI indicates that its equipment will lose less than 1% gas volume per year, or it will perform the repair to make it right under warranty. Consistent with ITC's vision and goal, a prominent sign within the Mitsubishi factory indicates that the company takes leak controls seriously: "No Leak Too Small … We Catch 'em All."

The alliance partnership established for outdoor switchyard transmission-class circuit breakers served as the impetus for ITC to further explore the abilities of MEPPI to supply GIS replacements. A separate substation department within MEPPI handles GIS, and conceptual design meetings began in March 2005. At the first and subsequent design meetings, discussions revolved around technical details of the state-of-the-art replacement for the failing GIS at the St. Antoine substation.

A major challenge of the St. Antoine GIS replacement was the requirement that, at most, only one-third of the normal 120-kV load could be removed at any given time. This challenge alone required several custom interfaces between the existing and new GIS to keep two-thirds of the 120-kV station load fed at all times.

The existing bus was of the welded design, which increased the difficulty of the fieldwork that would be necessary to install the interfaces. The schedule was fairly aggressive, such that within the three-month construction phase, there would be the replacement of a three-circuit-breaker ring bus connected to three 24/32/40-MVA transformers, a solid dielectric underground cable and two high-pressure gas-filled underground cables.

In addition, the congested vicinity of St. Antoine GIS in downtown Detroit afforded little construction lay-down space for staging and storing materials. Therefore, the scheduling of materials for just-in-time delivery was another challenge MEPPI had to meet.

In performing due diligence of other GIS suppliers' economics and abilities, ITC found that only MEPPI had the experience of replacing GIS in part, while keeping portions energized and serving load during the construction process. While it was a calculated risk to attempt such an endeavor, MEPPI had recently completed two similar replacement in-part projects for Southern California Edison (Rosemead, California, U.S.), which included replacing failing 230-kV and 550-kV GIS at Serrano. The 230-kV substation replacement resulted in a total of 14 MEPPI breakers, making this the largest 242-kV GIS installation in North America.

After weighing all of its options, ITC decided that given the risk and visibility of its project, and in support of its newly forged alliance partnership, MEPPI was the logical choice. ITC and MEPPI also agreed to use M.J. Electric, LLC (Iron Mountain, Michigan) as the installation contractor. This was another risk-reducing measure for the St. Antoine GIS project, because MEPPI and M.J. Electric had worked together previously and recently completed a GIS project for Commonwealth Edison of Chicago, Illinois, U.S. (see T&D World, July 2008).