Evaluating Current Standards of Seismic Qualifications of Substation Equipment and Applying to Other Regions of the World

Maintaining operability and performance of the grid during and after a seismic event is crucial for system operators, as the consequences of failure can disrupt power supply to customers, damage critical and costly equipment, and even negatively impact the environment due to oil spill and runoff. In the past decade, both the frequency and geographical range of earthquake influence has increased affecting wider areas that are not typically seismic prone.

Due to the unpredictability of a seismic event in magnitude, frequency and location, the approach to seismic design is quite different from those used in designing components sustaining loads from high-speed winds or floods. Seismic structure design often considers multiple load paths and structure ductility to ensure structural integrity, to control structure damage and prevent collapse, and most importantly to ensure the structure and/or equipment remain functional. For substation equipment supporting structures, the approach is similar with modifications to better suit utility common practices; however, for substation electrical equipment, the process is much more stringent and could be considerably more conservative when compared to seismic design of structures. This is mainly because many components of electrical equipment, such as bushings, are made of brittle materials, like porcelain, with low ductility. Damage to these electrical components could potentially cripple the functionality of substation equipment and could result in a power disruption.

In this paper, the authors will first briefly discuss the background of seismic qualification of substation electrical equipment and its methodologies that are different from seismic design of structures. The authors will then present the updates made to the latest versions of two documents commonly referenced by utilities around the world that provide guidance on substation equipment seismic qualification: IEEE 693-2018 (and its associated amendment

IEEE 693a-2024) and IEC 62271-207:2023. The paper will discuss results from comparing the two documents and assessing their alignments and note the changes from the previous versions.

Next, results from a literature review of available seismic qualification procedures around the world will be presented with discussions on how similar standards compare to IEEE 6932018/693a-2024 and IEC 62271-207:2023. Lastly, the authors will outline guidance for utilities to effectively qualify their seismic equipment in locations where there is no seismic qualification standard available based on the results of the comparison of the references previously presented. Potential challenges and barriers to adopting the guidance will also be discussed. The goal of this paper is to provide utilities with a better understanding of current standards of seismic qualification of substation electrical equipment and to provide the guidance of procedures for those areas with no available standards to prevent power disruption and strengthen utility grid resilience.