Peak structure in PD spectra of hydrogenerators through “HF grounding” of the couplers and “time and amplitude” calibration

In order to develop a reliable tool for the maintenance planning of hydrogenerators, research works have been pursued to improve the immunity to noise of the “differential” technique of partial discharge measurements (PD). In this paper is presented 1) the “high-frequency grounding” technique that has been developed at IREQ to improve the signal-to-noise ratio of PD measurements systems and 2) the “time and amplitude” calibration technique that has been concurrently developed to achieve the low noise levels required for PD spectra measurements. Following the implementation on hydrogenerators of the HF grounding technique and of the enhanced calibration technique, noise-free PD spectra have been obtained. It is believed that these noise-free spectra will be more sensitive for the monitoring of the insulation conditions with time and for the detection of insulation defects at their early stages of development