PMDT Acoustic Contact
PD inside of oil-filled equipment or SF6 equipment will have an acoustic emission at a high frequency near 90kHz in SF6 and near 160kHz in oil. These emissions do not travel through air. The contact probe is used by placing the sensor onto the transformer or GIS tank. A vacuum gel is used to bridge the airgap and ensure the signal is received by the probe. Acoustic contact measurements are very sensitive. Very small PD signals can be detected and characterized. Also because they travel at the speed of sound, the origin of the signals can be triangulated using multiple sensors simultaneously.