At the live testing site of zinc oxide surge arresters, test personnel often find that the results of two measurements on the same phase have large dispersion, or that the resistive current reading deviates significantly from historical data. After excluding the aging factor of the arrester itself, the state and operation mode of the tester are often key variables. Design and selection personnel understanding the maintenance points of the instrument can help reduce data fluctuations during the procurement and use stages.
Q: The reference voltage input range of the tester is nominally 10V～200V. Can it be measured directly when the voltage on the low-voltage side of the PT is low?
A: The reference voltage input range (peak value) is 10V～200V, and it can be customized to 0～250V. If the voltage on the low-voltage side of the PT is lower than 10V, it is necessary to confirm the minimum input threshold of the instrument, and if necessary, expand the range through customization. Before measurement, the PT transformation ratio and the actual voltage on the secondary side should be checked to avoid angle calculation deviation caused by an excessively weak input signal. For the measurement ranges of total leakage current, resistive current, and capacitive current, all are 100uA～8mA, and can be customized to 0～20mA. During selection, the current interval should be estimated according to the arrester model and operating voltage, leaving an appropriate margin.
Q: During daily maintenance, which operations are likely to affect angle measurement accuracy?
A: The angle measurement range is 0°～360°, with a resolution of 0.01°. During on-site wiring, the voltage sampling and current sampling should maintain a corresponding phase relationship to avoid installing the clamp current transformer in the reverse direction. If the tester has not been calibrated for a long time, the internal clock or sampling channel may drift, and it is recommended to send it for inspection according to the metrological cycle. The instrument should be stored away from strong magnetic fields and humid environments to prevent sensor zero drift.
Q: How can selection be completed when the measurement voltage and current ranges are uncertain?
A: First obtain the arrester operating voltage, continuous operating current, and expected resistive current component. If only the test voltage on the low-voltage side of the PT needs to be measured, the reference voltage range can cover 0～250V; if the total current and resistive current need to be analyzed, then focus on whether the basic range of 100uA～8mA is sufficient. For high-precision analysis occasions, a customized 0～20mA range can be considered. It should be noted that the upper limit of the measurement range is not the larger the better; an excessively wide range may reduce the resolution of small signals.
Q: When poor reading repeatability occurs in on-site testing, from which aspects should troubleshooting be carried out?
A: First check whether the grounding is reliable and whether the voltage and current leads are far away from interference sources. Second, confirm that the tester has sufficient battery power, as low battery may affect sampling stability. Finally, check the cleanliness of the arrester surface and the weather conditions. If multiple measurements are still inconsistent, a known stable reference component can be used for comparison to determine whether it is an instrument problem or a test object problem.
