Principle of Surge Arrester Measurement and Method for Evaluating Test Results Performance

Surge Arrester Measurement Principle
To determine whether a zinc oxide surge arrester has aged or become damp, the change in resistive current flowing through the arrester under normal operating voltage is typically observed, specifically by checking whether the resistive leakage current has increased.
Resistive leakage current often accounts for only 10% to 20% of the total current; therefore, it is difficult to determine changes in the resistive current of zinc oxide surge arresters merely by observing variations in the total current. The resistive leakage current must be separated from the total current.
The arrester tester relies on a voltage reference signal, rapidly sampling the reference voltage and arrester leakage current. Using harmonic analysis and fast Fourier transform, it separately calculates resistive components (fundamental and harmonics) and capacitive components.

Resistive current fundamental = total current fundamental × cosΦ, where Φ is the phase angle difference between the total current and the voltage fundamental.
Surge Arrester Performance Evaluation
When the fundamental component of resistive current increases significantly while harmonic content shows little change, it generally indicates severe contamination or moisture.
When the harmonic content of resistive current increases significantly while the fundamental component shows little change, it generally indicates aging.
The bottom capacitive current remains unchanged only when the surge arrester undergoes uniform degradation. When uneven degradation occurs, the bottom capacitive current increases. The bottom capacitive current reaches its maximum increase when half of the surge arrester has degraded.
Phase-to-phase interference affects the test results but does not compromise their validity. The longitudinal comparison method using historical data can effectively reflect the operating condition of zinc oxide surge arresters.
Arrester performance can be assessed by the fundamental component of resistive current, but it is more effective to evaluate it based on the phase angle difference Φ between current and voltage, since 90°−Φ corresponds to the dielectric loss angle. If the resistive current is specified to be less than 25% of the total current, the corresponding angle Φ would be 75°.