The Chilean Transmission System’s response to a major earthquake in February 2010 exposed serious vulnerabilities, notably failure of conventional equipment and components located far from the quake’s epicenter. These failures underscored the need to re-evaluate seismic criteria then in effect.
Experts conducted the reassessment in two phases: the first, from 2010 to 2012, focused on investigating the nature of damage and underlying causes. This culminated in a set of recommendations. The second phase, conducted between 2016 and 2018, aimed to formally develop updated seismic requirements tailored to the country’s electrical infrastructure.
This edited contribution to INMR by Marcela Aravena at Ingtegral Engineering Services presents Chile’s development of a rigorous seismic standard for electrical substations which are dominated by high-magnitude subduction earthquakes. The new standard aims to integrate equipment, structural, and geotechnical requirements while taking account of their seismic interaction to ensure post-event operability and infrastructure resilience. She also outlines how this process led to publication in January 2025 of Chile’s legally binding Seismic Requirements.
Chile is among the most seismically active countries in the world. Accordingly, it has national seismic standards for residential buildings and industrial facilities. However, at the time of the 2010 earthquake, no seismic standard existed specifically for high voltage electrical facilities.
Official seismic requirements for electrical facilities in Chile are outlined in the Technical Standard for Safety and Quality of Service and its annexes, issued by the National Energy Commission. As of 2009, this regulation required that substation equipment must meet the seismic criteria defined in either the Chilean Standard ETG 1.020 or IEEE Std 693-1997. It did not, however, include seismic requirements for support structures or foundations of that equipment. According to interpretation of IEEE Std 693 by Chilean engineers at the time, specifying seismic requirements only for electrical equipment would be sufficient to ensure a facility’s operability post-earthquake.
State-of-the-Art Design of Electrical Substations as of 2010
1. Official Seismic Requirements for Electrical Facilities Before Feb. 2010
• Electrical equipment: to meet the seismic criteria defined in either the Chilean standard ETG 1.020-1998 or the international IEEE Std 693-1997.
• No seismic requirements were specified for the support structures or foundations of that equipment.
2. Unofficial Seismic Requirements for Electrical Facilities before Feb. 2010
Chilean structural engineers used to design equipment support structures and foundations with seismic requirements based on ETG-1015 (ENDESA, 1987), a document developed following the 1985 earthquake (magnitude 7.8) and grounded in that event’s seismic experience. However, by 2000, as new Chilean engineering firms began participating in substation projects, most were unfamiliar with ETG 1.015. Also, from 2005 on, the transmission system saw increasing involvement from international transmission companies who typically brought their own engineering standards, often from regions with much lower seismic activity.
3. Seismic Situation for Electrical Facilities by 2010
In summary, by 2010, substations in Chile were characterized by the following:
• Equipment built to comply with either IEEE Std 693 (1997 or 2005) or ETG 1.020 — the latter being less rigorous and outdated compared to the IEEE standard;
• Equipment support structures either followed well-known Chilean seismic guidelines (usually rigid structures) or failed to meet these as in the case of flexible structures;
• Structures and foundation were designed based primarily on the Chilean Static Method, even when the support structure was not rigid;
• Equipment foundations that either followed unofficial Chilean seismic practices or did not meet seismic expectations;
• Mostly traditional foundation types as shown in Fig. 1 (slab with pedestal).
Analysis of Electrical System Performance in 2010
CIGRE Chile formed a Special Study Committee to assess how transmission facilities performed during the event. The failures observed during the February 27, 2010 earthquake can be classified into the following categories:
i.) Breakage of equipment mounted directly on their own support structures (Image 1).
ii.) Breakage of equipment due to a rigid electrical connection (Image 2)
iii.) No damage to the equipment itself, but failure in the electrical connection between the equipment and the substation (Image 3).
iv.) Equipment materials that were expected to behave in a ductile manner but instead exhibited brittle failure.
v.) Failure of transformer anchoring systems to their foundations due to design flaws — specifically, the absence of seismic stops to absorb shear forces (Image 4).
vi.) Damage and collapse of equipment installed on top of firewalls (Image 5).
vii.) Collateral damage to nearby equipment caused by the “projectile effect” of components mounted on failed firewalls (Image 5).
Photo from [9].
Photo from Reference [9].
Photo from Reference [9]
• Equipment behavior is influenced by the support structure and/or foundation, emphasizing the role of seismic interaction;
• Numerous equipment failures were caused by inadequate support structure;
• The ETG 1.020 spectrum may not be inherently sufficient.
• There is a clear need for a seismic code that addresses entire electrical facilities, not just the equipment itself.
Topics Considered for New Chilean Seismic Standard
1. Type of Seismic Origin
In subduction earthquakes, such as those occurring in Chile, the energy accumulated before rupture can be extremely high, making them more powerful than other types of earthquakes. Subduction events are particularly notable for their high magnitudes and longer durations.
The significance of different earthquake types is acknowledged in IEEE Standard 693-2018, specifically in Clause 6.4.5:
“The application of spectral shapes presented in Figure A.1 and Figure A.2 may result in qualified equipment that have lower margins against failure when subjected to subduction zone earthquakes compared to crustal earthquakes. The possibility of subduction earthquakes needs to be evaluated when determining seismic requirements.”
Based on the above, Chilean seismic requirements included:
• Seismic requirements for electrical equipment are defined by seismic behavior groups. This type of classification enables the requirements to be applied to any equipment mentioned in the document, as well as to any other equipment with similar seismic behavior;
• Seismic load for electrical equipment plus other simultaneous loads such as short circuits;
• Differences in the Shake Table requirements compared to IEEE 693-2018:
◦ Input motion must have a duration of at least 45 seconds of strong motion rather than 20 seconds;
◦ Duration of the strong motion is the time interval between 10% and 90% of Arias Intensity.
2. Spectrum & Soil Classification at Site
The importance of soil classification lies in understanding its bearing capacity, deformation behavior, natural period or frequency of vibration, and potential for additional seismic amplification, among other factors. From a seismic perspective, soils are classified in descending order based on stiffness. Seismic parameters used to categorize soil types are defined in relevant national or international seismic standards.
Although specific parameters may differ between standards, the seismic soil classification and descriptions used in Chile are consistent with those established in ASCE 7-16.
Analysis of the ETG 1.020 Spectra (ETG A.020 by Transelec was also an unofficial seismic standard used for electrical equipment and its spectra is the same as the ETG 1.020) revealed that it is representative of seismic soils classified as Class A to Class C. This aligns with the system’s performance during the 1985 earthquake (the base event used to develop ETG 1.020), when most equipment was made of porcelain (ceramic).
In the 2010 earthquake, although most equipment was still made from similar materials, no damage was reported in substations related to soil behavior. However, damage was observed on transmission lines and in other types of national infrastructure. Today, most equipment is made from polymeric materials, which exhibit more flexible behavior compared to porcelain. Additionally, wind farm developments in southern Chile are primarily situated on Class D (softer soils).
Because of these factors, it became necessary to update the Chilean seismic spectrum to incorporate polymeric equipment on site Class D soils within the new seismic requirements.
For sites not classifiable within Classes A through D, a Site-Specific Seismic Study must be performed to establish a Design Response Spectrum (Article 20, Document [1]).
Fig. 2 shows the new Design Spectrum compared to those from ETG 1.020 and IEEE 693-2018. Fig. 3 shows the new Spectrum alongside those analyzed in Fig. 5 of the article Development of UHV Bushings for Extremely Severe Seismic Conditions, published by INMR. Although comparing spectra provides important information and is usually included in technical documents, it is insufficient for comparing seismic standards. It is necessary to consider that each spectrum has its own definitions and requirements that could vary according to different standards, such as soil class validity, support structure requirements, and other loads in addition to seismic loads, among others.
Seismic Interaction Between Soil Classification & GIS Equipment Behavior
Gas-Insulated Switchgear (GIS) is particularly sensitive to relative displacements between its components. Therefore, its seismic behavior is closely tied to shear waves or “S-waves,” i.e. surface waves that cause vertical ground movement while propagating horizontally. The amplitude of S-waves (vertical motion) tends to be lower on rigid soils and increases with more flexible soil conditions.
Given that Chilean earthquakes are typically subduction-type (long duration), manufacturers must consider the amplitude of S-waves when designing GIS equipment (Articles 62 to 66, Reference [1]). While this specific requirement for GIS has been officially included since 2025, it has been mandatory since 2020 for all High Voltage Facilities in Chile to include a geotechnical study at the project site. This study must provide all parameters necessary to classify the soil in accordance with national seismic regulations (Article 24, Reference [2]).
Seismic Behavior of Structure and/or Foundation in Relation to Equipment Supported
1) What does it mean that structure or foundation is inadequate?
This means that while the structure and foundation may be able to withstand seismic demands, their behavior under seismic loading causes amplification relative to the accelerations experienced by the equipment they support (the resonance effect).
Referring to the spectra in Fig. 2 and a peak ground acceleration (Ao) of 0.5g:
• If the equipment is mounted on a properly designed support structure and foundation, the acceleration at its base will be Ao = 0.5g, and the maximum acceleration at its center-of- gravity will reach 1.37g (or 1.61g, depending on the spectra applied).
• However, if the same equipment is installed on an inadequate support structure or foundation, both, the base and center-of-gravity, accelerations may significantly exceed these expected values.
2) How much higher can it be?
It depends on how flexible the structure and foundation system are in comparison to the equipment itself. Some recommendations and standards specify an Amplification Factor “Kh” for the horizontal seismic acceleration Ao = 0.5g.
This means that the horizontal acceleration for the equipment will be:
Kh ∙ A0 = Kh ∙ 0.5g at the base
Regarding this, the Chilean documents, and the IEEE Standard state the following:
3) Can a support structure and/or foundation be adequate for one equipment but inadequate for another?
Yes. The structure and/or foundation must be appropriate for the specific equipment they support.
If an equipment is replaced with another that differs in its seismic characteristics, it is essential to verify that the existing structure and/or foundation are suitable for the new equipment—even if it performs the same electrical function or operates at the same voltage level.
An equipment is considered seismically different when at least one of the following properties varies: total height, weight, location of the center of gravity, natural frequency of vibration, sensitivity to displacement, among others.
Amplification Factors for Equipment
Amplification factors represent the increase in seismic acceleration experienced by equipment due to the supporting structure’s dynamic behavior, particularly when the structure’s purpose is not exclusively to support the equipment.
Based on the analyses carried out by CIGRE Chile, Reference [6], and accepted by the committee cited in Reference [3], the following amplification factors have been established:
Kh = 3 for horizontal seismic acceleration
Kv = 1 or 1.4 for vertical seismic acceleration
In Chile, this situation occurs due to lack of space in substations, (Image 6) especially when updates are needed it (gantry photo in Image 7, and due for safety reasons as shown to the transmission line.
These values are considered realistic (i.e. not conservative). This means that the structural designer must incorporate rigid elements in the local area where the equipment is installed, ensuring that the seismic acceleration at the base of the equipment does not exceed Kh ∙ Ao for horizontal acceleration and Kv ∙ Av for vertical acceleration.
Conclusions
Why a Chile-specific standard?
Subduction earthquakes, like those that occur in Chile, release a great amount of energy and last significantly longer than other types. This means, among other things, that strong motion duration is longer than that considered in IEEE 693-2018. As a result, it is necessary to consider longer durations for strong ground motion in Shaking Table Tests, as well as other loads acting simultaneously with seismic loads.
Real seismic behavior of equipment is influenced by supporting structure and/or foundation, as well as soil class at installation site. This emphasizes the role of seismic interaction when defining seismic requirements for electrical facilities to ensure post-event operability and enhance infrastructure resilience.
Similarly, the seismic response of the ground at the site plays a critical role for equipment sensitive to relative displacements between components, such as GIS equipment. Since Chilean earthquakes are typically subduction-type and characterized by long durations, the amplitude of shear waves (S-waves) i.e. those which cause vertical ground motion while propagating horizontally, must be explicitly considered in design of such equipment.
Moreover, due to safety concerns and spatial limitations, some facilities require equipment to be mounted on structures that were not specifically designed to support them (see Images 6 & 7). This makes it essential to define seismic requirements not only for the equipment but also for these support structures.
Does the Chile-specific standard mean the IEEE Std 693 is no longer valid?
IEEE Std 693 is still valid. However, it is not sufficient: additional seismic requirements are necessary for the equipment, as well as for their support structures and foundations.
What do the new Chilean seismic requirements do?
• Define consistent seismic requirements for equipment, supporting structures, and foundations into a single document, ensuring that changes to one component require updates to the others;
• Define seismic requirements for electrical equipment by seismic behavior groups. This type of seismic classification enables the requirements to be applied to any equipment mentioned in the document, as well as to any other equipment with similar seismic behavior;
• Include soil seismic behavior as a variable, both in definition of Design Spectrum and in the procedures for sites with soil classified as unstable and/or prone to deformation;
• Address soil-structure interaction when designing displacement-sensitive equipment such as GIS;
• Introduce a mandatory role of “Seismic Reviewer” for each seismic design—not only for equipment, but also for structures and civil works (e.g., “Equipment Seismic Reviewer” and “Structure Seismic Reviewer”);
• Define clear responsibilities for all stakeholders involved in engineering, supply, construction and assembly phases.
REFERENCES
[1]. January 2025 – Chilean National Energy Commission: Public document “Seismic Requirements for High Voltage Electrical Facilities”, official document included as an Annex in the Safety and Quality of Service Standard.
[2]. January 2025 – Chilean National Energy Commission: Updated version of the 2020 public document “Minimum Design Requirements for Transmission Facilities”, official document included as an Annex in the Safety and Quality of Service Standard.
[3]. 2022–2023 – Chilean National Energy Commission: Public documents from the 10 Sessions of the Advisory Committee for the drafting of the official document on Seismic Requirements.
[4]. Jun 2019 – Presentation by Marcela Aravena at Chilean Engineers Association: “Seismic Loads for High Voltage Facilities: The need for a National Seismic Standard”.
[5]. December 2018 – Presentation by Marcela Aravena and Hernán Casar at the CIGRE Chile Tutorial: “Seismic Requirements for High Voltage Electrical Facilities. Toward a National Seismic Standard.”
[6]. 2018 – CIGRE Chile Publication: “Recommended Seismic Requirements for High Voltage Facilities”, Working Group led by Hernán Casar and Marcela Aravena.
[7]. IEEE Std 693-2018 – Recommended Practice for Seismic Design of Substations.
[8]. 2013 – ETG A.020 Version 8, Transelec. Seismic Design Specifications for High Voltage Electrical Facilities.
[9]. 2012 – CIGRE Chile Publication: “Lessons and Recommendations for the Electrical Sector Derived from the February 27, 2010 Earthquake in Chile.”
[10]. June 2011 – Presentation by Marcela Aravena and Hernán Casar at the Chilean Association of Engineers: “Lessons Learned in the Chilean Electrical Transmission System. Are the Seismic Specifications Adequate?”
[11]. October 2010 – Presentation by Marcela Aravena at the CIGRE Chile Seminar: “Seismic Design of Structures and Foundations in Electrical Transmission Facilities.”
[12]. IEEE Std 693-2005 – Recommended Practice for Seismic Design of Substations.
[13]. IEEE Std 693-1997 – Recommended Practice for Seismic Design of Substations.
[14]. ETG 1.020-1997 – Ingendesa: General Technical Specifications. Seismic Design Requirements for Electrical Equipment. Condensed version.
[15]. ETG 1.015-1987 – Endesa: General Technical Specifications. Seismic Design.
[16]. “Development of UHV Bushings for Extremely Severe Seismic Conditions.” Authors: P. Cardano, G. Testin, V. Fogliani, A. Pastore, M. Sehovac. Published by INMR.
