A state of the art used technology in linear accelerator chains is a microphone setup. A specific frequency range is filtered out of the spectrum, schmitt trigger behaviour at the input drives the arc detection circuit.

One of the technique that can measure or detect the PD is by using ultra high frequency (UHF) method for HV equipment insulation condition monitoring and assessment

https://link.springer.com/content/pdf/10.1007%2Fs13320-014-0146-7.pdf

Piezoelectric sensors

The choice of the optimal PD sensor depends on many factors, including the place of installation of the transformer (shielded HV laboratory of the transformer manufacturer or noisy power substation), the size of the transformer tank, or the type of PD measurements (detection, location or online monitoring).

For tests carried out in a test laboratory, the conventional IEC 60270 electrical technique is unrivaled (guarantees the highest sensitivity of detection). Together with the acoustic emission (AE) method, it can be used to locate PD sources using the advanced auscultatory technique (AAT). Of course, the PD location can be done using the AE method alone (TDoA technique, which requires a minimum of 4 AE sensors) or the combined AE / UHF method (usually one UHF antenna installed in the oil drain valve and at least 3 AE sensors). Good results can be achieved with the standard auscultation technique (SAT), in which one AE sensor is enough. The SAT technique allows you to find the place (s) in the vat where the AE pulses with the greatest amplitude and energy are recorded. Then, based on the analysis of the transformer construction diagrams, it is possible to deduce the location of the defect of the insulation system being the source of PD. The SAT technique is easy to use and, unlike the TDoA technique, it does not require a lot of experience. Unfortunately, it does not allow us to know the exact XYZ coordinates of the PD source, but only the XZ coordinates.

In turn, for power transformers tested at substations, in the presence of strong electromagnetic disturbances, we must use unconventional techniques of PD detection (the conventional technique of IEC 60270 is not immune to EM disturbances and therefore is not suitable for field measurements). For small units (power up to several MVA) you can even use a cheap high-frequency current transformer (HFCT sensor) and an oscilloscope. The situation becomes more complicated when we test a large power transformer. From my experience (I have performed PD tests on over 200 transformers), I can recommend the acoustic emission method. To obtain high sensitivity of PD detection, it is worth choosing low-frequency AE sensors (20 kHz - 100 kHz) instead of the popular 150 kHz resonance sensors. This is due to the fact that PDs generate AE signals in the 20-100 kHz band. Generally, the higher the discharge energy, the frequencies dominating from PD shift towards lower frequencies (20-60 kHz).

The UHF method seems to be the best choice if we plan long-term PD monitoring. The monitoring system based on the UHF method is unfortunately quite expensive, and its installation is a much greater logistical and technical challenge than in the case of the AE system. Therefore, the AE method will be sufficient for short-term PD monitoring (e.g. for one week). In order to obtain high diagnostic reliability, it is worth installing as many AE sensors as possible (8 or 16-channel systems are popular and readily available).