Surge Protection Devices (SPDs) are critical components in safeguarding electrical systems from voltage spikes and surges. However, like any other device, SPDs can fail. Understanding the failure modes of SPD open-circuit and short-circuit—is essential for ensuring continuous protection and system reliability.
Open-Circuit Failure in SPDs
Open-circuit failure is a common mode of failure in SPDs, particularly those with varistors. This type of failure typically occurs due to the natural ageing process or thermal protection mechanisms. When an SPD reaches the end of its life, an internal disconnector is activated, rendering the SPD inoperative. This disconnector is designed to disable the SPD to prevent further damage.
In SPDs with gas discharge tubes, internal disconnectors (thermal protection) may also be used to protect against abnormal overheating caused by unexpected follow currents or surge currents. It’s important to note that thermal runaway, a common cause of failure in varistor-based SPDs, does not apply to SPDs with gas discharge tubes or encapsulated spark gaps.
A spark gap, another type of SPD, may fail in an open-circuit mode when it can no longer ignite an arc due to electrode wear or a faded electronic ignition circuit. In this state, the SPD becomes permanently open, leaving the system unprotected.
Why Open-Circuit Failure is Hard to Detect
One of the challenges with open-circuit failure is that it often goes unnoticed. Since the SPD is no longer operational, the system remains unprotected, but there are no immediate signs of failure. To address this, SPDs with failure indication functions are recommended. These indicators alert users when an SPD has failed, ensuring timely replacement before the next surge event.
Short-Circuit Failure in SPDs
Short-circuit failure is another critical failure mode that can have severe consequences. This type of failure can be caused by sustained abnormal over-voltage (TOV) or faults in the distribution system, such as neutral/phase switchover or neutral disconnection. Additionally, surges with unexpected energy levels can also lead to short-circuit failures.
When an SPD fails in short-circuit mode, the system is significantly impacted. The short-circuit current flows through the failed SPD, potentially causing excessive energy dissipation and fire hazards. To mitigate this risk, SPDs must undergo short-circuit withstand capability tests as outlined in the IEC 61643-11 standard.
The Role of Overcurrent Protective Devices
To further protect against short-circuit failures, external overcurrent protective devices, such as fuses, circuit-breakers, or RCDs, are often used in conjunction with SPDs. These devices act as backup protection, interrupting the short-circuit current and preventing potential fire hazards.
Compliance with IEC 61643-11 Standards
The IEC 61643-11 standard provides comprehensive guidelines for testing and verifying the failure modes of SPDs. It mandates that SPDs must have disconnectors (internal, external, or both) to ensure safe operation. Additionally, the standard requires that the operation of these disconnectors be indicated by a corresponding status indicator.
Thermal Protection and Arc Extinguishing Devices
Thermal protection is a critical feature in SPDs, designed to prevent overheating due to degradation or overstress. However, this test is not performed on SPDs containing only voltage switching components and/or ABD devices.
For enhanced safety, some SPDs are equipped with arc extinguishing devices. Porsurge patented to permanently and securely disconnected from the power system, cutoff AC arc /short circuit to prevent fire hazard
Conclusion
Understanding the failure modes of SPDs—open-circuit and short-circuit—is crucial for maintaining system protection and preventing potential hazards. By adhering to IEC 61643-11 standards and incorporating features like thermal protection and arc extinguishing devices, SPDs can provide reliable and long-lasting protection against surges and voltage spikes.
For more information on our surge protection devices and how they comply with industry standards, visit our www.prosurge.com
