How to test lightning arrester?
Diagnosing High Voltage Surge Arresters Effectively
Surge arresters are essential for safeguarding electrical devices and equipment in high-voltage substations. Like any other device, they require regular diagnostics to ensure they function properly. The most straightforward method of inspection is visual: ensuring there is no visible external mechanical damage.
However, internal damage can occur without any visible external signs, compromising the arrester's ability to protect against surges. To address this, Doble Engineering has developed monitors that detect leakage currents in surge arresters. In collaboration with Fluke Europe, they used Fluke’s handheld thermal imaging cameras to create a reliable diagnostic solution.
Testing High-Voltage Surge Arresters
The IEC60099-5 international standard outlines various methods to diagnose high-voltage surge arresters. Using this standard, we developed the LCM500 Leakage Current Monitor to perform non-invasive diagnostics on varistor-type surge arresters during their operation.
This instrument measures the quality of the metal oxide blocks, helping manage the risk of failure. Specifically, it employs IEC60099-5 method B2, analyzing the leakage current's 3rd harmonic with harmonic compensation in the grid voltage. According to the international standard, this is the most reliable method to diagnose high-voltage surge arresters during operation.
Confirming Results with Thermal Imaging
We tested the LCM500 at a 110kV/6kV overhead power line substation equipped with valve-type surge arresters. The L2 phase leakage current was significantly higher than the other two phases, indicating potential damage to the L2 phase arrester.
To verify our findings, we used the Fluke Ti450 Pro Infrared Camera, which is capable of capturing and visualizing very small temperature differences with high accuracy. Thermal imaging allowed us to confirm the LCM500's results, showing additional local heating in the L2 phase arrester.
This dual method of using the LCM500 and Fluke’s thermal imaging camera provided a reliable diagnostic solution. It confirmed that the LCM500 could effectively assess the technical condition of high-voltage, valve-type surge arresters. Note that the Fluke Ti450 Pro Infrared Camera has been updated to the Ti480 since the original publication of this case study.
Understanding Lightning/Surge Arresters
Lightning and surge arresters protect electrical installations from unpredictable electrical surges caused by internal factors like electrical faults and external events like lightning strikes. Over time, these arresters have evolved, with modern versions using Zinc Oxide (ZnO) which, although superior, can fail violently when degraded.
Factors like lightning strikes, electrical surges, moisture buildup, environmental contamination, and gradual aging contribute to this degradation. Monitoring the health of these arresters involves understanding their electrical equivalent circuit which consists of a resistive component (R) and a capacitive component (C).
Techniques for Testing Surge Arresters
Three primary techniques are used to evaluate the health of surge arresters:
1. Tan Delta Measurement
This technique monitors the resistive current (Ir) to identify degradation trends in the arrester.
2. Insulation Resistance Test / Leakage Current Test on DC
This method isolates the resistive current (Ir) but is less accurate in providing a complete health assessment.
3. Third Harmonic Resistive Leakage Current Measurement
This online measurement technique uses a specialized clamp-on ammeter to measure the third harmonic resistive component, offering the most reliable results without requiring a shutdown.
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Resistive Leakage Current or Power Loss Measurement
According to IEC 60099-5, resistive leakage current or power loss can be measured using eight different methods, classified as A1 to A4, B1 to B3, and C. B1 and B2 methods generally provide the best results, with B2 offering the most accurate health analysis by compensating for harmonic errors in the system voltage.
Advanced Tools
SCOPE SA 30i+ is a state-of-the-art wireless leakage current analyzer designed to assess the residual life of Metal Oxide Surge Arresters. It measures total leakage current and third harmonic resistive leakage current according to IEC 60099-5-B2 standards, even in hostile electrostatic noise environments.
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