About zinc oxide arrester charged measurement knowledge

Zinc oxide surge arresters (MOA) play a crucial role in protecting electrical equipment from overvoltage caused by lightning and switching surges. However, due to aging of the valve discs and damage from heat and mechanical stress, these devices can fail, potentially leading to explosions or short circuits in the substation busbar, which may compromise the entire power system’s stability. As a result, it is essential to perform regular preventive tests and on-line monitoring. However, traditional pre-tests often require the main equipment to be shut down, which is not always feasible due to operational constraints. This makes live testing and continuous monitoring particularly important. Live testing of MOAs is conducted without disconnecting the equipment, allowing for real-time assessment of the arrester’s condition. During this process, several factors can influence the test results, including electromagnetic interference from nearby energized equipment, improper measurement techniques, and surface contamination. To ensure accurate results, it is vital to adopt reliable testing methods that minimize such interferences. The working principle of MOA is based on zinc oxide varistors, which exhibit high resistance under normal operating voltages but rapidly switch to a low-resistance state when exposed to overvoltage. This allows the surge current to be safely diverted to ground, protecting the connected equipment. The key performance indicator during testing is the ratio of resistive current to total leakage current, as an increase in the resistive component often indicates internal degradation or moisture ingress. To enhance the accuracy of live testing, different methods are employed, such as the secondary voltage reference method, induction plate method, and harmonic analysis. Among these, the secondary voltage method is considered more reliable due to its stable data output, although it requires coordination with other teams. The induction plate method, while convenient, is highly susceptible to external interference, making it less precise. Angle correction is also a critical step in improving measurement accuracy, especially when measuring three-phase MOAs arranged in a straight line. Due to phase-to-phase coupling, the measured phase angle (φU-Ix) can deviate, leading to inaccurate readings. By applying correction angles, the true value of the phase difference can be obtained, ensuring more reliable assessments of the arrester’s health. In addition to testing, proper technical management of MOAs is essential. This includes maintaining detailed technical files that record all test results, on-line monitoring data, and factory reports. These records help track the performance of each arrester over time and support informed maintenance decisions. Despite advancements in testing and monitoring, some failure causes remain unclear, highlighting the need for ongoing research and improvement. Future efforts should focus on refining testing procedures, reducing device complexity, and enhancing the accuracy of live measurements to ensure the safe and reliable operation of MOAs in power systems.

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