During routine testing of 10kV gapless metal oxide arresters (MOA), O&M personnel often encounter the following situation: when using an arrester characteristic tester to measure the DC 1mA voltage (U1mA), the reading fluctuates and has poor repeatability; when reading the leakage current at 0.75U1mA, the value is easily affected by the environment and wiring. The problem often lies not in the arrester itself, but in the wiring method of the test circuit and the habits of parameter reading.
The tester needs to judge internal defects such as poor contact between MOA valve discs before the thunderstorm season, and its core basis is the leakage current at U1mA and 0.75U1mA. If there is common-mode interference between the reference terminal of the DC high-voltage output and the grounding terminal of the arrester, or if the high-voltage lead is too long and the shielding layer is suspended, the microampere-level leakage current measurement will deviate from the true value. On site, the grounding terminal of the tester should be connected to the grounding down-conductor of the arrester as close as possible, and the high-voltage output line should be as short as possible and kept away from the grounding loop to avoid forming an additional loop.
The intelligent arrester characteristic tester can measure parameters such as full current (fundamental RMS and peak value), resistive current (including positive and negative peak values and various harmonics), capacitive current, power-frequency reference voltage, active power, and phase difference, and display the real-time waveforms of voltage and current through a large-size LCD touch color screen. O&M personnel can observe whether the DC voltage boost process is stable and whether the leakage current shows abnormal jumps, thereby judging whether the wiring is reliable and whether the arrester valve discs show signs of moisture or aging. When reading, the value should be recorded after the voltage boost is stable for several seconds, avoiding taking values during the voltage ramp-up process.
In the parameter verification stage, the dispersion of U1mA is more informative than a single absolute value. If multiple measurement results of the same phase arrester deviate significantly, the grounding and shielding should be checked first, and then the arrester condition should be considered. The leakage current at 0.75U1mA should preferably be read after the U1mA measurement is completed by reducing the voltage to 0.75 times that point, reducing the disturbance to the valve discs caused by repeated voltage boosts. The rechargeable power supply design facilitates continuous on-site operation, but it should be noted that the output voltage stability may decrease when the battery is low, so the battery status should be confirmed before measurement.
