About zinc oxide arrester charged measurement knowledge

Zinc oxide surge arresters (MOA) are widely used in power systems due to their excellent overvoltage protection characteristics. However, aging of the valve discs and damage caused by heat or mechanical shocks can lead to failure. In severe cases, this may result in explosions or short circuits in the substation busbar, posing a serious threat to system safety. As a result, it is crucial to perform regular preventive tests and on-line monitoring of MOAs. However, traditional pre-testing often requires the main equipment to be powered down, which may not always be feasible due to operational constraints. Therefore, live testing and real-time monitoring have become essential practices. Live testing of zinc oxide arresters presents several challenges, such as electromagnetic interference from adjacent energized equipment, improper testing methods, and environmental factors like surface contamination. These factors can significantly affect the accuracy of test results. To ensure reliable performance, it is important to use proper testing techniques that minimize these interferences. The working principle of MOA relies on zinc oxide varistors, which exhibit high resistance under normal operating voltages but rapidly switch to a low-resistance state when exposed to overvoltage conditions. This allows them to divert excess current safely to ground, protecting electrical equipment from damage. The ability of the varistor to return to its high-impedance state after the overvoltage event makes MOA an effective and durable protective device. The importance of live testing lies in identifying early signs of internal degradation, such as moisture ingress or aging of the valve disc. By measuring the resistive current component relative to the total leakage current, technicians can assess the health of the arrester. An increase in the resistive current indicates potential internal faults, which may lead to further deterioration if left unchecked. Several factors influence the accuracy of live testing, including phase-to-phase interference, sensor placement, and the method used for measurement. Among the available techniques, the secondary voltage reference method is considered more accurate and stable compared to the induction plate method, which is more susceptible to external interference. However, the secondary voltage method requires coordination with other teams and access to the PT secondary voltage, making it less convenient in some scenarios. Angle correction plays a vital role in improving the accuracy of measurements, especially when testing three-phase arresters arranged in a straight line. Phase-to-phase coupling can cause shifts in the measured phase angle between voltage and current, leading to incorrect readings. Applying an appropriate correction angle helps restore the true relationship between the voltage and current signals, ensuring more reliable results. In practice, technical management of MOAs involves maintaining detailed records of each device, including factory reports, test results, and on-line monitoring data. This ensures that any changes in performance can be tracked over time. Despite the advancements in MOA technology, some failure causes remain unclear, highlighting the need for continued research and improvement in testing methodologies. In conclusion, live testing of zinc oxide arresters, particularly using the secondary voltage method and incorporating angle correction, provides a more accurate assessment of their condition. This approach helps avoid misdiagnosis and ensures the safe and reliable operation of power systems. Future improvements should focus on simplifying testing procedures to enhance their practicality in the field.

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