The demands on the modern electric grid are enormous – and only growing.
Our society lives increasingly in a digital world and sees electrification as the key to fighting back against the effects of climate change. Substations occupy a critical place in the electric power delivery system, stepping voltage down or up as needed from power plants to users.
The new second edition of Substation Structure Design Guide, Manual of Practice 113, has arrived to help structural designers of outdoor electrical substation structures and foundations, utility engineers, and manufacturers address today’s demands and anticipate those to come. It updates what’s changed in the 16 years since the original was issued in 2008.
The Structural Engineering Institute’s Task Committee on Substation Structural Design took on revising the original manual of practice, led by editor George T. Watson, P.E., M.ASCE, whose expertise in substation design spans more than 50 years. Watson spoke with Civil Engineering Source about the new guide and how it will help engineers design and build substations that will stand up to current and future demand.
Source: It’s been 16 years since the first edition. What was the spark behind producing a new edition?
Watson: Some ASCE/SEI Electrical Transmission Structures committee members asked me to chair the revision committee since I was vice-chair of the first edition. We felt it was time to update the MOP. There were questions on how to use the MOP that consistently came up, and we felt we could address those topics to help users. It was also an opportunity to update the MOP with current information for the design of substation structures.
Source: How extensive are the changes?
Watson: The revision started as a minor evolution and to add a very brief chapter on foundation types used in substations. As we progressed, newer and better hazard maps became available in ASCE 7, and we wanted to include the best available content. One major change was the design of anchor bolts. Another change was the first edition had a simple seismic philosophy. The second edition has greatly expanded the seismic content and equations to be more compatible with ASCE 7 and IEEE 693 (Seismic Design of Substations).
Source: How involved was the process of drafting the new edition? Were there any surprises? Any unexpected challenges that proved difficult to address?
Watson: One large challenge was using MS Word. The committee consisted of 33 engineers who designed substation structures, so the use of MS Word to write a technical document with its references and headings, plus subheadings, tested our soft skills set. The other challenge was in-person meetings and making progress between meetings. The pandemic was also a challenge, with virtual meetings to address over 800 peer-review comments.
Source: What guidance might be considered the biggest change since the first edition?
Watson: The second edition recommends that anchor bending is always considered where base plates are supported on leveling nuts. The first edition and industry practice followed ASCE Standard 48, where bending could be neglected if the gap between the top of the concrete and the bottom of the base plate was less than twice the anchor bolt diameter. New equations were developed to always include bending stress.
Source: The ASCE 7-22 standard is a basis for some of the manual’s guidance. How is it applied?
Watson: ASCE 7-22 has the most current hazard maps for buildings and “other structures,” and we used the maps as they apply to substation-type structures. The MOP uses loading combinations that are applicable to substation structures with utility practice load factors and method of application.
[Note: The free online ASCE Hazard Tool is available at ascehazardtool.org.]
Source: What do you think this manual of practice improves upon most in the current practice of designing and building substations?
Watson: Until the first edition was published, there were limited reference sources where an engineer could go to find design information for substation structures. The second edition adds some content, such as a generic foundation chapter to list some foundation types used in substations. We have also added an appendix for a deeper dive into short-circuit forces. A chapter on oil containment and barrier walls has been added, along with the retrofit of existing structures.
Substation Structure Design Guide, Manual of Practice 113, is available in print and e-book formats in the ASCE Bookstore.
