Common Fault Diagnosis and Troubleshooting Guide for Low-Voltage Surge Protective Devices (SPDs): Safeguarding Electrical Equipment

Low-voltage Surge Protective Devices (SPDs) serve as critical defenses in

protecting electrical equipment against lightning strikes and overvoltage impacts. However, during actual operation, SPDs themselves may

experience various failures. Understanding the causes of these common

faults and mastering precise troubleshooting methods is essential for

maintaining the safety and stability of power supply systems.

Common Fault Types and Mitigation Strategies:

Degradation/Failure of Insulation

Causes: Excessive environmental humidity, natural aging of

insulating materials, physical impact damage.

Troubleshooting: Thoroughly inspect the SPD housing and

insulation components. Clean surface contaminants and ensure the device is dry. If insulation material aging or physical

damage is confirmed, replace the entire SPD immediately.

Erosion/Failure of Spark Gap (Electrodes)

Causes: Exposure to lightning surges exceeding design specifications or cumulative damage from frequent strikes.

Troubleshooting: Perform regular visual inspections of the

spark gap. If severe electrode erosion, deformation, or loss of proper discharge function is observed, replace the SPD or have the spark gap professionally repaired (depending on

product design).

Excessive Leakage Current

Causes: Aging and degradation of internal components

(e.g., Metal Oxide Varistors - MOVs), leading to reduced

insulation performance.

Troubleshooting: Precisely measure the SPD's leakage current

under operating voltage using a multimeter or dedicated

leakage current tester. If the leakage current exceeds the

manufacturer's specified safe threshold, replace the SPD

promptly.

Internal Thermal Runaway

Causes: Abnormal internal component heating (potentially due

to sustained overvoltage, aging, or degradation), ultimately causing insulation failure.

Troubleshooting: Verify ventilation and heat dissipation

conditions at the SPD installation site, ensuring ambient

temperature complies with product specifications. If internal components are damaged due to thermal runaway, replacing the device is the only solution.

Inadequate Grounding System

Causes: Loose/corroded ground connection points or excessive

grounding resistance.

Troubleshooting: Periodically tighten ground connections and

measure grounding resistance, strictly ensuring it is ≤ 10 Ω (complying with relevant standards). If grounding issues are found, rework the connections or replace/upgrade the

grounding system.

Improper Installation Location

Causes: SPD installed too far from the protected equipment,

using excessively long or thin connecting conductors.

Troubleshooting: Optimize the installation location to place

the SPD as close as possible to the protected equipment. Use short and thick (sufficient cross-section) connecting conductors to minimize the detrimental

effect of lead inductance on protection performance.

Status Indicator Failure

Causes: Internal circuit failure within the indicator or

external physical damage (e.g., broken window).

Troubleshooting: Check the indicator display status. If

confirmed inaccurate (e.g., permanently green, no change,

or physically damaged), replace the indicator module or the

entire device (depending on model).

Systematic Troubleshooting Procedure:

Initial Inspection:

Visual Inspection: Carefully examine the SPD housing for cracks, deformation, bulging, scorch marks, discoloration, or other abnormalities.

Status Indication: Verify the indicator color or marking to

preliminarily determine if the device is functional

(e.g., Green/Normal, Red/Failed).

Electrical Performance Testing:

Leakage Current Test: Measure the SPD's leakage current under

operating voltage using appropriate instruments. Compare

results against specifications to assess health.

Insulation Resistance Test: With the SPD de-energized (and disconnected if necessary), measure the

insulation resistance between terminals and between terminals and ground, confirming compliance with safety standards.

Protection Function Verification:

Simulated Surge Test: Apply standard surge waveforms

(e.g., combination wave) using a professional surge generator to test the SPD's performance characteristics (clamping voltage, energy handling capability, response time) against

requirements.

Protective Operation Check: Confirm the SPD activates effectively to divert surge energy during simulated tests, and that the status indicator changes correctly (e.g., from Green to Red).

Grounding System Verification:

Ground Resistance Measurement: Precisely measure the grounding

system resistance using an earth resistance tester, ensuring ≤ 10 Ω.

Connection Integrity Check: Visually and manually inspect ground wire connections at the SPD's ground terminal and the ground rod/network for tightness, absence of corrosion, and unbroken strands.

Maintenance and Replacement Decisions:

Regular Cleaning & Maintenance: Keep the SPD surface clean and

dry to prevent dust/dirt accumulation and moisture ingress.

Preventive Replacement: Strictly follow the manufacturer's recommended service life, periodic test results, and operating

environment (e.g., high lightning activity areas) to

proactively replace aged, degraded, or end-of-life SPDs.

Conclusion:
Implementing regular preventive inspections, standardized electrical

testing, functional verification, and diligently following the

troubleshooting steps outlined above enables the effective identification and timely resolution of potential issues in low-voltage SPDs. Consistently selecting high-quality products, ensuring correct installation and reliable grounding,

and adhering to a schedule of periodic testing and maintenance

significantly extends SPD service life and continuously optimizes its

protective performance, building a robust and reliable safety barrier for the power supply system.