January 26, 2004

Turnkey Circuit-Switcher And Trans-Rupter II^® Installations Improve System Reliability.

Background

To improve system reliability, a large Southern U.S. electric utility needed to upgrade the fault protection scheme for ten 134/13.8-kV transformers and one 67/13.8-kV transformer. In the existing arrangement, fault clearing was achieved by tripping the bus and line circuit breakers — taking the entire high-voltage bus off line; a motor-operated air-break disconnect switch on the high side of each transformer would then open to isolate the transformer. Only after all the transformers had been isolated and the system operator had located the faulted transformer through SCADA could the disconnect switches of the unfaulted transformers and the breakers be closed, bringing these loads back on line.

Traditionally, the utility handles the engineering and construction work for such upgrade projects in-house. But they were required to complete and use the budgeted dollars for this project before the end of the calendar year . . . and it was already June! They simply didn&rst have the resources available to complete this fast-paced project on schedule.

S&C’s Services and Products Solutions

The utility turned to S&C’s Power System Services to perform the engineering, procurement, installation, testing and commissioning work on a turnkey project basis. Power Systems Services’ engineers got right to it, scheduling field visits, talking to structural steel fabricators, drawing up concept designs, and reviewing protection schemes with utility engineers.

An S&C Series 2000 Circuit-Switcher or a Trans-Rupter II® Transformer Protector was chosen as the protective device at each transformer location. The existing protection scheme would need to be modified to trip only the Circuit-Switcher or Trans-Rupter II Transformer Protector of the affected transformer — a much more desirable arrangement.

But there would be challenges in installing the new equipment. Careful project management and planning would be essential to complete all the work on time, as equipment outages had to be scheduled well in advance with the utility’s planning department.

Unique mounting structure designs would be needed, capable of withstanding hurricane-force winds of 120 mph. In some instances, non-standard foundations and modification of existing structures would be necessary. See physical design below:

Space was also an issue. At three locations, the existing motor-operated disconnect switch would need to be relocated to allow installation of an S&C Series 2000 Circuit-Switcher. At other locations, space was so limited the only solution would be a Trans-Rupter II mounted on a 30-foot high steel structure; a special S&C Type LS-1 Switch Operator would be needed to automatically sequence the operation of the existing disconnect switch with the Trans-Rupter II.

Utility’s Foresight Helped to Accomplish the Goal

The utility had previously established a General Service Agreement with S&C. S&C was thus in the position to support the utility’s engineering staff if and when required, and also perform product maintenance and repairs quickly. Having the agreement in place further allowed the contract process for this project to proceed smoothly, eliminating delays associated with negotiating contract terms and conditions.

Services Provided by S&C

S&C provided a wide variety of services for this project, specifically:

• Physical design engineering, including foundations, structural steel, layout, grounding, and conduit.
• Protection and control engineering, including single-line diagrams, electrical schematic and wiring diagrams, cable and conduit tables, SCADA RTU point assignments, and existing relay panel modifications.
• Specification and procurement of all equipment for the project, including seven Series 2000 Circuit-Switchers, four Trans-Rupter II Transformer Protectors, four Type LS-1 Switch Operators, structural steel, protective relays, wire and cable, and conduit.
• Equipment installation, including foundations, switch erection, and wiring.
• Testing and commissioning of the Series Circuit-Switchers, Trans-Rupter II Transformer Protectors, and new protection scheme.
• Project management and site management.

Results

The results exceeded the utility’s requirements. S&C completed the project within budget . . . and almost two full months ahead of schedule. The utility is very pleased with S&C’s work and is looking to utilize S&C’s Power Systems Services to perform additional transformer protection upgrade projects in the near future.