In live testing of zinc oxide surge arresters, it is common to observe significant dispersion in measurement results for the same phase across two tests. This is partly related to the separation algorithms used by the tester for parameters such as total current and resistive current, and also associated with the anti-interference design of the discharge tube tester itself. The following analyzes the measurement characteristics of surge protective component discharge tube testers from several comparative dimensions.
There are differences in the separation methods for total current and resistive current. Some instruments use harmonic analysis, extracting the fundamental and various harmonic components through Fourier transform; another type combines hardware filtering with software compensation. Discharge tube testers typically can measure total current (fundamental RMS and peak value), resistive current (including positive and negative peak values and various harmonics), capacitive current, etc. Technicians need to pay attention to the impact of their harmonic suppression capability on the repeatability of the positive and negative peak values of resistive current.
Attention should be paid to the measurement conditions for reference voltage and phase difference. The measurement of power-frequency reference voltage is relatively sensitive to the phase accuracy of the voltage sampling signal. When a discharge tube tester measures active power and phase difference, if there is an inherent phase shift between the voltage and current channels, it will directly affect the calculation results of resistive current. During on-site comparison, one can observe the phase difference reading deviations of different instruments on the same arrester.
There are clear boundaries for environmental adaptability. According to product technical data, the storage temperature of the discharge tube tester is -10~+45°C, and the humidity is +85%RH. Exceeding this range may affect the stability of internal references and components, leading to measurement drift. In humid or high-temperature sites, it is recommended to check whether the actual use and storage conditions of the instrument meet these parameters.
Operation and wiring methods affect comparability. The wiring differences between live testing and de-energized testing are significant. During live measurement, discharge tube testers typically use clamp-on current sensors to obtain current signals and obtain voltage signals from PT or busbars. When comparing data from different instruments, one should first confirm whether the method of obtaining the reference voltage is consistent; otherwise, the absolute values of total current and resistive current are not directly comparable.
Selection comparison should be carried out around measurement needs. If focusing on the insulation degradation trend of the arrester, emphasis should be placed on the repeatability of the fundamental and third harmonic of resistive current; if factory parameters need to be verified, power-frequency reference voltage and total current peak value are more critical. The multi-parameter comprehensive measurement capability of surge protective component discharge tube testers provides a comparable data basis for different purposes.
