In high-seismic zones, the seismic resistance of electrical equipment in substations and industrial and mining power distribution rooms serves as the last line of defense for maintaining power supply after a disaster. Compared to building structures, switchgear cabinets have a high center of gravity, precision internal components, and complex cable layouts. Under the combined vibrations of seismic P-waves and S-waves, they are highly susceptible to failures such as cabinet tilting, structural deformation, unintended switch operation, and busbar fractures. According to national seismic design standards, core power equipment must pass vibration table tests simulating a rare magnitude 9 earthquake to ensure it remains upright, intact, and operational after an earthquake. There are significant differences in structural rigidity, mounting methods, and seismic redundancy among various types of switchgear. Among them, the 24 kV switchgear and air-insulated switchgear (AIS) commonly used in power grids and industrial and mining facilities are the mainstream equipment prioritized for testing, optimization, and upgrading in high-seismic-risk areas; their seismic performance directly determines the post-earthquake recovery capability of the power distribution system.
Many on-site operations and maintenance personnel hold a misconception: they believe that heavy switchgear is inherently earthquake-resistant. In fact, conventional switchgear cabinets without seismic reinforcement are highly susceptible to resonance failure under high-frequency repetitive vibrations. To verify equipment reliability under extreme conditions, the industry commonly uses vibration test benches to simulate real seismic waveforms, replicating the acceleration, frequency band, and duration of a rare magnitude 9 earthquake, thereby comprehensively evaluating the cabinet's structural integrity, mechanical performance, and electrical stability. This article combines standardized vibration test protocols to compare the seismic performance of different types of switchgear, focusing on analyzing the seismic weaknesses and reinforcement solutions for 24 kV switchgear and air-insulated switchgear (AIS).
1. How Severe Is a Rare Magnitude 9 Earthquake? Core Risk Factors for Seismic Failure of Switchgear
A rare magnitude 9 earthquake constitutes an extreme operating condition beyond design criteria, with peak ground acceleration far exceeding conventional seismic design standards and vibration frequencies spanning the natural resonance range of switchgear. For power distribution equipment, seismic damage is not a single impact but rather a series of oscillations and torsional vibrations lasting tens of seconds, which can easily trigger equipment resonance and cause both structural and electrical damage.
From an operational perspective, post-earthquake failures in switchgear can be broadly categorized into three types: first, deformation of the cabinet frame, loosening of anchor bolts, and cabinet overturning, resulting in total equipment write-off; second, unintended tripping of internal circuit breakers and isolating switches due to seismic shaking, leading to power outages and short-circuit faults; and third, loosening or breakage of busbars, insulators, and secondary wiring, causing electrical circuit failure. Different types of switchgear have distinct structural designs, and their failure risks vary accordingly.
Conventional air-insulated switchgear (AIS) features an open cabinet design with relatively lightweight support structures and overall low rigidity, making it prone to excessive cabinet sway and component loosening during vibrations; In contrast, the primary medium-voltage 24 kV switchgear contains numerous internal components, features wide busbar spans, and has a high center of gravity, making it highly prone to resonance. It poses significant risks such as insulator fracture and busbar displacement, and is therefore a key focus of seismic testing in strong-seismic zones.
2. Seismic Performance of Different Switchgear: Differences in Equipment Under Vibration Table Testing
Under standardized vibration table test conditions simulating a rare magnitude 9 earthquake, various types of switchgear exhibited distinct performance tiers. Structural rigidity, overall stability, and seismic redundancy directly determined the success or failure of the tests, providing a clear basis for equipment selection in high-seismic-risk areas.
Air-insulated switchgear (AIS), relying on air insulation and an open cabinet layout, features a simple structure and relatively light weight, resulting in significant sway during seismic vibrations. AIS equipment that has not undergone specialized seismic reinforcement is prone to issues such as deformation of the enclosure sheet metal, jamming of operating mechanisms, and loosening of external leads during testing. However, due to its distributed structural stresses and the absence of rigid, enclosed compartments that cause tensile forces, its seismic stability can be significantly enhanced-and the basic power distribution requirements for high-seismic-risk areas met-as long as proper foundation reinforcement and position-limiting restraints are implemented.
As core medium-voltage equipment for industry and power grids, 24 kV switchgear features a regular cabinet structure with concentrated loads; however, its overall center of gravity is relatively high, and it contains a dense array of precision internal components. Under high-frequency vibrations of magnitude 9, standard cabinets are highly prone to resonance, leading to circuit breaker drawer displacement, cracking of insulating supports under stress, and loosening of busbar terminals. Therefore, qualified 24 kV switchgear must incorporate specialized designs-such as structural reinforcement, damping optimization, and limit-stop protection-to successfully pass vibration table limit tests.
3. Successfully Passing the 9-Degree Seismic Test: The Core Design Logic Behind the Switchgear's "Weeble-Wobble" Mechanism
Switchgear capable of passing a 9-degree rare-event earthquake shake table test does not rely on its own weight to withstand pressure. Instead, it employs a systematic seismic design approach-comprising "structural reinforcement, resonance avoidance, limit locking, and stress dispersion"-to endow various types of switchgear with seismic self-healing and stability capabilities, truly ensuring that the equipment "does not tip over, does not collapse, and does not malfunction" during an earthquake.
First, Enhanced Rigidity of the Overall Frame to Strengthen the Structural Foundation
To address the weaknesses of 24 kV switchgear-namely, a high center of gravity and susceptibility to resonance-an all-welded frame with reinforcing ribs is employed. This enhances the overall rigidity of the cabinet and reduces the amplitude of vibration-induced deformation. Thicker base connection plates and a dual-bolt fastening structure prevent base slippage and loosening during seismic events, thereby eliminating the risk of cabinet tilting or overturning at its source.
Second, a dedicated limit-stop locking design prevents component displacement
Seismic limit-stop devices are installed on movable components such as circuit breaker drawout units, isolating switches, and secondary terminals to restrict displacement deviations caused by seismic vibrations. Specifically addressing the looseness inherent in the open structure of air-insulated switchgear (AIS), mechanical stops and anti-loosening latches are added to prevent operating mechanisms and external components from misalignment, jamming, or detachment due to seismic shaking.
Third, resonance frequency optimization to avoid the seismic vibration range
By adjusting structural counterweights and damping modules, the natural vibration frequency of the cabinet is altered so that the resonance range of various types of switchgear avoids the high-frequency vibration band associated with a magnitude 9 earthquake. This prevents resonance-amplified deformation and significantly reduces seismic damage to the equipment's structural and electrical performance.
Fourth, optimization of electrical connection flexibility to withstand deformation-induced tension
Flexible connection structures are adopted for busbars and secondary wiring, allowing for vibration-induced deformation. This prevents minor cabinet deformations from pulling on cables and terminals, thereby eliminating secondary faults such as post-earthquake wire breaks, short circuits, and insulation damage, and ensuring the continued integrity and operability of electrical circuits in 24 kV switchgear and air-insulated switchgear (AIS) after an earthquake.
4. Value of Testing: Seismic Resistance Is Not a Gimmick-It Is the Safety Baseline for Power Distribution in High-Seismic-Risk Areas
A rare magnitude 9 earthquake represents a low-probability, high-risk extreme scenario. The core significance of shake table testing lies in simulating extreme disaster scenarios to verify the fault-tolerance and post-disaster availability of switchgear. For power systems in high-seismic-risk areas, power distribution equipment does not need to emerge "unscathed" from an earthquake, but it must "remain standing, avoid collapse, and be capable of rapidly restoring power."
Fully seismic-optimized 24 kV switchgear can maintain the stability of the main power supply infrastructure even under extreme seismic conditions; reinforced and upgraded air-insulated switchgear (AIS) can effectively prevent component detachment and mechanical failure, ensuring the normal operation of branch circuits. Standardized seismic upgrades for various types of switchgear establish a multi-layered seismic protection system for power distribution networks in high-seismic-risk areas, providing core support for rapid post-disaster grid restoration and the maintenance of power supply for both residential and industrial needs.
Conclusion
Truly reliable switchgear not only handles routine operating conditions smoothly but also withstands the extreme tests of natural disasters. The rare magnitude 9 seismic shake table test reveals the true seismic resilience of power distribution equipment. From core 24 kV switchgear to air-insulated switchgear (AIS) suitable for a wide range of applications, all types of switchgear must undergo rigorous seismic testing to be deployed in high-intensity seismic zones. Through structural optimization, limit protection, resonance avoidance, and flexible adaptation, power equipment is designed to possess the resilience of a "roly-poly toy," ensuring that every switchgear unit becomes a solid bulwark for the power grid's seismic resilience and supply security.
About us
Zhejiang Lvma Electric Co., Ltd., established in 2018, draws on 17 years of collective industry expertise. As an ISO 9001:2015-certified manufacturer, we specialize in intelligent switchgear systems and both oil-immersed and dry-type distribution transformers. Our products reach customers in Europe, the Middle East, South America, Southeast Asia, and Africa.
With over 40 patents held by our R&D team, we are advancing from a traditional producer to a technology-driven provider of smart energy solutions. Digital manufacturing and real-time monitoring systems ensure our equipment delivers consistent safety, efficiency, and reliability.