After decades in operation, utilities often face the inevitable reality that their unit substations are old, overloaded and potentially a maintenance concern. Alabama Power Co. is one utility currently looking for alternatives in refurbishing its system. The utility found the perfect opportunity to address aging unit substations.

THE SITUATION

Alabama Power serves a community in the Birmingham, Alabama, U.S., metro area that has particular challenges inherent in the terrain: heavily wooded areas with estate homes. This area is served by 13.2-kV to 4-kV unit substations that combine the transformer, voltage regulation and low-side overcurrent protection in one package. A large number of the distribution lines are located off road and along rear property lines. Due to the limited rights-of-way, conversion to a higher voltage is not possible. The unit substations serving the area were several decades old, had become heavily loaded and continued maintenance had become a concern. It was clear that replacement of the unit substations was needed. Alabama Power needed a solution that would lower the overall cost, minimize the size of the installation's footprint, present a design that is aesthetically pleasing, ensure safety and security, and greatly reduce the amount of ongoing maintenance.

Alabama Power evaluated Cooper Power Systems' padmounted substation design as a possible replacement for the dated unit substations. The relatively small footprint and dead-front padmounted design made it an ideal solution for this particular location. In addition, the option to have the padmounted transformer, reclosers and voltage regulators preinstalled on a steel pallet would make the installation quick and eliminate the need for time-consuming cable installation between the components.

An additional confidence factor was that Gulf Power (Pensacola, Florida, U.S.), a sister Southern company, had used Cooper Power's padmounted modules and was pleased with their performance and reliability. Alabama Power decided that Cooper Power's Modular Integrated Transportable Substation (MITS) would meet the utility's requirements.

MITS TECHNOLOGY SOLUTION

The MITS turnkey process capability was an important factor in Alabama Power's selecting this solution. Cooper assembled all the components — controls, wiring, transformers, reclosers, regulators and other equipment — into a working substation that was mounted onto a self-supporting steel base. The fully integrated, factory-assembled system was wired and tested, including protection, control and automation devices.

The project consisted of replacing one unit substation transformer at three different substation sites, each of which consisted of two unit substation transformers. Initially one unit substation transformer at each site was replaced with the MITS technology. It is anticipated that additional units will be installed at each of these sites, dependent on the success of the initial installations.

Site preparation for installation consisted of simply preparing a concrete pad for the steel pallet and installation of the cables for connecting to the existing overhead 13.2-kV and 4-kV systems. The MITS units were delivered to the substation sites on flatbed trailer trucks, lifted by crane from the trailer and placed onto the concrete pads. From crane to placement, it only took about half a day to set the substations, reducing the time needed for substation replacement from several days to just a few hours.

Electric power in this particular area is stepped down by these units from 13.2 kV to 4 kV. Elements of each substation include:

• Padmount reclosers with a Form 6 control

• Padmount regulators with a CL-6A control

• 3750-kVA padmount transformer

• Single-phase station service padmount transformer

• 600-A molded-rubber “T” body interfaces on all padmounted modules.

PROJECT BENEFITS

Using the turnkey approach is a great advantage to implementing MITS technology. Comparing this process with that of constructing a conventional substation, it reduces the number of people involved in the design and construction process, which helps avoid delays and potential communication issues. Normally, the utility would be working with design personnel, construction personnel, checkout personnel (for SCADA equipment), steel shop personnel, a transformer manufacturer, a recloser manufacturer and other manufacturers to complete a substation project. Alabama Power would have to design the substation, purchase all the components, keep track of delivery and then assemble each of them on site.

With the modular substation approach, Cooper engineers the MITS configuration — including the interconnection of the substation components, system analysis, design and specification — coordinates the procurement of the proper equipment from multiple factories, gets it to the job site on time and assists, if necessary, with the construction phase of the project. Although Alabama Power is comfortable with working with multiple suppliers of products on projects, dealing with one company to develop a lock-and-key package helped streamline the process and expedite the in-service date.

The utility anticipates the same high quality that can be expected from traditional substation designs while, at the same time, realizing reductions in field labor, cost and project time line due to the system's modularity. And since the MITS units are all dead-front, and the dead-front connections are in a locked cabinet, the connections are protected from the elements, which will reduce maintenance needs during the life of the units.

Due to the heavily wooded nature of the substation sites, there was a concern that leaves and other natural debris would build up between the padmounted units. This issue had the potential to significantly increase the amount of maintenance required to keep each substation clean. Cooper actively addressed the situation and worked with the steel pallet manufacturer to design a cover to fit between the padmounted units to prevent any leaves, debris or other natural elements from falling into and accumulating in the crevices over time.

In addition to cost savings, the project met the utility's aesthetic requirements. The integrity of the heavily wooded area needed to be preserved. A traditional overhead-fed substation would require protective fencing due to the exposed live parts. Couple this with drastically increased installation time, and the construction could have created a prolonged inconvenience to our customers. With modular padmount substations, all the equipment and connections are within tamper-proof metal enclosures, and the feeder conductors are underground, which presents an aesthetically pleasing, low-profile-type design that blends into the environment. The cable and control wires are pulled through the trays and built directly into the skids. The appearance of the modular substations, with their components housed in attractively painted, unobtrusive enclosures, has increased aesthetic appeal compared to the steel structures of an overhead substation.

The flexibility of MITS technology also met the constraining space requirements of the project. The substation lots were limited in all three instances. Since the replacement substations were installed at the existing substation sites, reducing the project footprint proved to be a key benefit. Cooper's compact specifications fit appropriately within the existing space, resolving an issue that could have proved problematic with a traditional substation.

MITS technology's complete dead-front design also adds to the overall public safety of the project. The dead-front connections are in a locked cabinet that are safe and secure. This is a key feature that protects against unauthorized access as well, increasing the modular substations' overall safety and reliability.

ENVIRONMENTAL BENEFITS

Working with Cooper on this project gave Alabama Power the opportunity to use its environmentally friendly EnviroTemp FR3 dielectric fluid, which offers many benefits compared to traditional dielectric fluids (nonconductive fluids used to insulate and cool electrical distribution products such as transformers), including added performance and enhanced environmental characteristics.

EnviroTemp FR3 fluid uses base food-grade soybean oil, which is proven to be nontoxic according to guidelines developed by the Organization for Economic Cooperation and Development, a worldwide standard-setting organization. It is also biodegradable based on testing done by the U.S. Environmental Protection Agency.

EnviroTemp FR3 fluid is advertised to extend insulation life by five to eight times, lowering life-cycle costs. Tests have shown this dielectric fluid can increase performance during peak usage times when consumers are using more electricity, because it allows transformers to increase power loads without leading to premature insulation failure.

It also has increased fire-resistant qualities. Two nationally recognized testing laboratories, UL and FM Global, have listings allowing EnviroTemp FR3 transformer installations outdoors and indoors, typically without costly fire-protection devices. With higher-than-average flash points, this fluid provides maximum protection against transformer malfunctions and will not cause negative effects to the environment in the event of an incident.

MOVING FORWARD

MITS technology has helped Alabama Power accomplish its initial project goals of lowering the overall cost, minimizing the size of the installation's footprint, presenting a design that is aesthetically pleasing, ensuring safety and security, and improving the reliability. In addition, the implementation of EnviroTemp FR3 fluid provides an environmentally friendly solution and has the potential to increase the life of our new transformers.

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G. Bruce Shattuck began his electric utility career with Alabama Power as a student engineer in 1969 and graduated from the University of Alabama with a BSEE degree in 1971. He progressed through various positions of increasing responsibility to his present position of principal engineer in the Power Delivery — Distribution Engineering Services group. He is past chairman of the Southeastern Electric Exchange UD Committee and Distribution System Testing Application and Research (DSTAR) Committee. He is an active member of the Association of Edison Illuminating Companies (AEIC) Cable Engineering Committee and serves as the Southern Company lead product engineer for underground cables. GBSHATTU@southernco.com