When design and selection personnel face GIS partial discharge testing tasks, they often encounter a specific problem: there is obvious electromagnetic interference on site, while the sensitivity, frequency band, and range specified in the tester selection parameter table appear similar. Whether the tester can actually stably capture partial discharge signals during the operation of hydraulic or compressed air drive mechanisms needs to be checked item by item from the engineering parameter level. The operating mechanisms of GIS switches are mostly hydraulic drive or compressed air drive. To confirm the reliable working performance of the drive system, the motor needs to be started regularly to perform work and pressurize. Such motor start-stop and valve actions will generate pulse-type interference. If the anti-interference design of the tester is insufficient, weak partial discharge signals are easily submerged.
The frequency band and anti-interference circuit are the first items to check. Partial discharge testers are usually equipped with high-frequency elliptical scanning and time-base display circuits. The high-frequency time-base ellipse can be adjusted to normal size according to an input voltage of 10–250 V, and its absorbed power is less than 3% (based on full scale). During selection, it should be confirmed whether the elliptical scan can maintain stable synchronization within the range of power-frequency voltage fluctuations, avoiding phase display deviation caused by voltage waveform distortion. For GIS sites, models with a gate display circuit or phase windowing function should be preferred, so that the display window is aligned with the phase interval where partial discharge may occur, suppressing interference in irrelevant phase sections.
The range and voltmeter configuration directly affect the reliability of test voltage monitoring. A common test voltmeter range is 100 kV, with a 100 kV voltmeter resistor R, and a 3.5-digit digital voltmeter is used for display, with error controlled within ± (specific values are subject to the product technical documents). During design and selection, it is necessary to check the isolation method between the voltmeter and the partial discharge channel to ensure that no additional noise is introduced between the voltage application circuit and the measurement circuit. If the test object has a large capacitance, the matching of the coupling capacitor and detection impedance should also be considered to avoid signal attenuation or waveform distortion caused by impedance mismatch.
Multi-channel and wiring methods affect on-site efficiency. Some partial discharge testers support multi-channel switching, allowing all tests to be completed with one wiring setup, and are suitable for multi-winding reactors, motors, and other equipment. For GIS, if multiple gas compartments or bays need to be monitored simultaneously, models with low crosstalk between channels should be preferred, and it should be confirmed whether switching operations generate operating overvoltage pulses. For portable models that can quickly detect the partial discharge status of high-voltage electrical equipment on site, volume and weight parameters also need to be included in the selection trade-off.
Maintenance and calibration steps cannot be ignored. The tester should regularly check the linearity of the elliptical scan, voltmeter error, and channel consistency. Before on-site use, a known pulse calibrator can be used to inject a quantitative charge to verify whether the gain of the detection impedance and amplifier chain has drifted. For GIS rooms where hydraulic or compressed air drive mechanisms operate frequently, it is recommended to observe the background noise level during motor startup periods and set thresholds accordingly to avoid false alarms.
The selection conclusion usually comes down to the matching of three groups of parameters: whether the frequency band and anti-interference circuit can adapt to the on-site electromagnetic environment, whether the voltmeter range and error can cover the test voltage, and whether the channel configuration and wiring method can meet the gas compartment monitoring requirements. Comparing these three items with the operating characteristics of the GIS operating mechanism has more engineering reference significance than simply comparing nominal sensitivity values.
