**A: Main Issues of Zinc Oxide Surge Arresters:**
1. Zinc oxide surge arresters can be affected by environmental factors such as rain, snow, dust, and other contaminants. These elements may create a potential difference between the inner zinc oxide valve and the outer porcelain housing, leading to radial discharge. This phenomenon can damage the entire arrester and reduce its effectiveness over time.
2. The arrester is subjected to high-voltage surges, which cause the valve disc to age due to the energy from these impacts. Over time, this aging process reduces the arrester’s ability to protect electrical systems.
3. Since zinc oxide arresters are gapless, they must conduct current under normal operating voltage. The active component of this current generates heat in the zinc oxide disc, altering its volt-ampere characteristics. This creates a positive feedback loop, accelerating aging and potentially leading to thermal breakdown if left unchecked.
4. Moisture inside the arrester or poor insulation performance of the insulating bracket can increase the power frequency current, causing higher energy consumption. In severe cases, internal discharges may occur, further compromising the device's integrity.
**II: Instrument Test Principles and Features**
1. The software allows for automatic voltage reference detection, eliminating the need to connect to a PT (Potential Transformer). This feature can be enabled or disabled via the software interface.
2. The instrument uses FPGA-based hardware sampling and program-controlled amplification technology, increasing the sampling rate to 200 kHz. This ensures accurate capture of original current and voltage signals, improving test stability and reliability. It also effectively filters out high-frequency harmonics and interference.
3. On-site testing is made easier through the use of an internal lithium-ion battery and wireless data transmission, allowing for greater mobility and convenience during field operations.
4. With an embedded industrial processor, the instrument offers faster processing speeds, easier configuration, and the ability to simulate various algorithms. This increases transparency in testing methods and makes the device more versatile as an analytical tool.
5. The three-phase simultaneous testing capability helps eliminate interphase interference. This feature can be activated through the software, enhancing the accuracy of measurements.
6. The software includes functions such as device management and database management, with a unified interface between the host computer and the instrument for seamless operation.
7. The instrument measures voltage and current signals, performs fast Fourier transforms, and calculates both capacitive and resistive components (including fundamental and harmonic frequencies), providing detailed analysis of the arrester’s condition.
**III: Theory and Practical Conclusions**
1. The capacitive current at the base remains stable when the arrester degrades uniformly. However, if the degradation is uneven, the capacitive current increases. When half of the arresters are damaged, the capacitive current at the base reaches its peak.
2. The fundamental component of the resistive current shows a significant increase. If harmonic content does not rise much, it often indicates serious damage or moisture ingress.
3. Interphase interference may affect test results but does not invalidate them. Using historical data for longitudinal comparisons provides a more accurate reflection of the arrester’s operational status.
4. When the harmonic content of the resistive current increases significantly, but the fundamental component remains stable, it typically indicates aging of the arrester.
**IV: Why Resistive Current Testing Matters**
Resistive current testing is essential for identifying whether a zinc oxide arrester is experiencing aging or moisture-related issues. Under normal operating conditions, the resistive current is usually a small portion (10–20%) of the total current. Therefore, simply observing the total current change is not sufficient to detect subtle variations in the resistive component.
To accurately assess the condition of the arrester, it is necessary to isolate the resistive leakage current from the total current. This allows for a clearer understanding of how the resistive current is changing over time, helping to identify early signs of deterioration and ensuring timely maintenance.
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