Creating civil engineering standards
Most utilities have some level of electrical and physical design standards for their substations. These standards typically focus on the way a utility implements their yard layouts, grounding, conduit, and other considerations. Many of the details and drawings for the electrical and physical design also have common civil design elements.
This raises an interesting question – should a utility create civil engineering standards for their structures and foundations? There are a number of factors that determine if this is a sound and reasonable choice.
To standardize or not to standardize; that is the civil question
Cost is a primary consideration when upgrading an existing substation or creating an entirely new one. This work inevitably entails the installation of structures and foundations to support new electrical equipment. How do civil engineers contribute to this effort? The answer is design.
Civil engineers will typically design the structural support for a new piece of equipment, followed by the design of the supporting foundation. Both of these key design elements are repeated for the entire substation, and then translated into construction detail drawings to be built. All of the designs must meet site-specific loading criteria as well as any utility requirement for the strength and stability of that specific structure and foundation.
When it comes to standardization of civil design, it is possible to streamline the design process.
Three steps to standardizing civil designs
Utilities can save costs through standardized design processes. Here are three steps to consider:
Step 1: Identify the most common structures and foundations that are utilized in your substations. The list may be long, so focus on the most repetitive installations. Structures with repetitive installations typically consist of line terminals, rigid bus supports, switch stands, instrument transformer supports, and surge arrester supports. For pad-mounted foundations, circuit breakers and transformers generally top the list of common installations.
Step 2: Identify the most common equipment ordered by your procurement department. Focus on vendors that have supplied high quality equipment over the years. Identify equipment that is cost-effective and performs well. Additional economies can be gained from forming relationships with these vendors to obtain additional volume discounts on equipment that can be ordered in bulk, and stocked in your store rooms as a standard.
Step 3: Identify your service territory’s most extreme environmental loads and common soil types. This is a key step in developing civil engineering standards. The goal is to be able to use these standards without costly re-engineering every time you use these standards for an installation. For example, in the Midwest region, identify the most common extreme wind speed, ice loading, and subsurface soil conditions; on the West coast, seismic conditions are a typical consideration. By designing for these conditions, the resulting standard structure and foundation designs should be adequate for your entire service territory, less any special situations which may not fall into the typical category such as less than adequate soil conditions.
Implementing civil engineering standards requires initial planning, internal coordination, and upfront costs. The result, however, delivers versatile designs for both structures and foundations that can be implemented without repetitive design engineering costs for each and every project. The initial cost and effort are offset over time by the savings and efficiencies gained with each subsequent substation project. Additionally, standardized designs can result in cost savings associated with bulk material ordering, standard sizes, and available spare parts that fit the standardized designs.