Persistent Equipment Failures Despite SPD Usage: Unveiling Potential Causes

Key Takeaways

Oversized Surge Protection Devices (SPDs) can allow smaller, more frequent transient overvoltages to bypass protection, gradually degrading equipment.
Failure to implement cascaded transient voltage mitigation leaves equipment vulnerable to both failure and misoperation.
Equipotential differences compromise mitigation efforts, leading to imbalances that compromise sensitive components.
Equipment immunity levels should align with protection strategies to ensure reliable system operation.

Introduction

The adoption of surge protection devices (SPDs) is at an all-time high, driven by increasing code requirements. Despite this, equipment failures and misoperations caused by transient overvoltages persist and, in some cases, are even on the rise. This paradox highlights systemic issues in SPD application and system integration.

This paper explores the most common reasons for these failures:

Oversized SPDs
Not following IEEE’s recommended practice of applying a cascaded transient voltage mitigation system
Equipotential differences
Common mode SPDs inducing excess voltage onto equipment due to high current transient overvoltage events on ground

By addressing these challenges, this Tech Note aims to provide actionable insights for hardening systems against transient overvoltage and enhancing overall system reliability.

Is Your TVSS Sized Properly?

Selecting the right SPD requires a thorough understanding of an electrical system’s voltage environment and the immunity levels of individual equipment.

Equipment immunity levels refer to the maximum transient overvoltage a device can withstand without sustaining damage or performance degradation. Matching these levels to the SPD’s protection capability is critical. Fortunately, determining an immunity level is straightforward. According to both EPRI and the IEEE, equipment with electronics should not be exposed to transient overvoltage exceeding twice its nominal voltage. With the proliferation of electronics, we can take a conservative estimate by declaring an immunity level of 2X the nominal voltage.

Research by the Electric Power Research Institute (EPRI) indicates that correctly sized Type 2, Type 3, and Type 4 SPDs provide superior long-term defense against repetitive impulses, which gradually degrade equipment. Lower clamping SPDs, being more responsive to frequent transient overvoltages, ensure sustained mitigation from cumulative damage.

This aligns with the IEEE 1100-2005 (Emerald Book), which notes, “While electromechanical devices can generally tolerate voltages of several times their rating for short durations, few solid-state devices can tolerate much more than twice their normal rating.” The progressive deterioration of semiconductor junctions in solid-state devices underscores the importance of appropriate SPD selection to mitigate such vulnerabilities.

Importance of a Cascaded Transient Voltage Mitigation System

SPDs are categorized into Type 1, 2, 3, and 4, with each type serving a specific purpose:

Type 1 SPDs: Installed at the service entrance to defend against external transient overvoltage events like lightning strikes or utility faults. Typically placed on the line side of the main service disconnect.
Type 2 SPDs: Installed on the load side of service equipment, offering additional advantages to Type 1 including internal surges.
Type 3 and Type 4 SPDs: Located closer to equipment, these mitigate transient events affecting individual devices and sensitive electronics.

IEEE recommends implementing a cascaded transient voltage mitigation system, which strategically combines multiple SPD types at different points in the electrical network. This layered approach ensures comprehensive protection by addressing both externally generated (uncommon) and internally generated (common) transient overvoltage events. For example, a Type 1 SPD at the service entrance provides a first line of defense against externally generated transient overvoltage events like lightning, while Type 2 and Type 3 SPDs closer to sensitive equipment mitigate the residual overvoltage the Type 1 SPD could not dissipate as well as the more common localized transient overvoltages originating from load switching.

Failure to adopt a cascaded approach is most likely the leading cause of transient overvoltage equipment failure despite SPD usage. Most SPD utilization is only installed at the service entrance and is not sized to mitigate the more frequent transient overvoltage events. In electrical systems with multiple panels, a single SPD at the service entrance cannot appropriately harden the electrical system to mitigate equipment failure from transient overvoltage.

Has the Electrical System Been Bonded Properly?

Bonding is a cornerstone of electrical system integrity, providing a safe, low-impedance path for fault currents and reducing the risk of electric shock and fire.

Equipotential differences within an electrical system occur when grounding paths are inconsistent or impeded, creating variations in voltage levels at different points. These differences disrupt the uniform distribution of fault events, leading to localized voltage increases that can bypass the SPD and travel through sensitive equipment. Even with an SPD installed, these equipotential variations can introduce destructive voltage imbalances, particularly in systems with long conductors or multiple grounding points that are not properly bonded.

Such differences are exacerbated in complex electrical systems where multiple panels or circuits create additional challenges. High transient overvoltages, originating either internally or externally, can cause voltage increases between bonding points, leading to the degradation or outright failure of sensitive electronic components. Addressing equipotential differences requires not only ensuring low-impedance paths but also proper bonding connection and adherence to IEEE standards to minimize risks and enhance SPD effectiveness.

Common Mode SPDs Inducing Excess Voltage onto Equipment

While SPDs are designed to minimize the effects of transient overvoltage events, common mode SPDs can inadvertently introduce excess voltage onto equipment during high current transient overvoltage events from grounded objects. MOVs, a key component in modern SPDs, are nonlinear in their clamping actions—allowing more voltage to pass through as the current increases. During transient overvoltage events, such as lightning strikes propagating on grounding conductors, this nonlinear behavior can result in significant voltage being “backdoored” into the protected circuit. This occurs because the MOV is not a one-way device; it will pass voltage regardless of its source. But this scenario is alleviated when no connection exists.

In these scenarios, the transient overvoltage on the grounding conductors can propagate through the SPD and into sensitive equipment causing failure when the overvoltage exceeds the immunity level of the protected devices.

Read our Tech Note on common mode SPD application for a comprehensive analysis:
Maxivolt.com/home/concerns-with-common-mode-spd-application

Conclusion

Effective transient overvoltage mitigation is essential for safeguarding sensitive equipment and ensuring system reliability. However, their effectiveness depends on proper sizing, strategic implementation, and adherence to correct grounding and bonding practices. Equipment failures after SPD installation can arise from oversizing SPDs, or relying solely on single-point protection strategies. By overcoming these challenges, facilities can significantly enhance equipment operation, reduce failures, and minimize process disruptions.

Resources

Pattison, M., Hansen, M., Bardsley, N., Thomson, G. D., Gordon, K., Wilkerson, A., SSLS, Inc., LED Lighting Advisors, Bardsley Consulting, PlanArchology, Pacific Northwest National Labs, & Guidehouse, Inc., “2022 Solid-State Lighting R&D Opportunities,” DOE BTO Solid-State Lighting Program
Kladar, D., Martzloff, F., Nastasi, D., Eaton Electrical, Surges Happen!, & EPRI Solutions, “TOV effects on Surge-Protective devices,” 2005.
EPRI Power Quality Knowledge Program, “Protecting Against Surges and Temporary Overvoltage”, PQ TechWatch, Electric Power Research Institute (EPRI), August 2011
F. D. Martzloff, “Surge Protection Techniques in Low-Voltage AC Power Systems,” INTELEC – 1979 International Telecommunications Energy Conference, Washington, DC, USA, 1979, pp. 86-93, doi: 10.1109/INTLEC.1979.4793608.
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Electric Power Research Institute, “Characteristics of Lightning Surges on Distribution Lines, Second Phase – Final Report”, Research Project 2542-1, December 1991