Ekard GROSSMANN - Institute of Power Transmission and High Voltage Technology, University of Stuttgart Germany
Kurt FESER - Institute of Power Transmission and High Voltage Technology, University of Stuttgart Germany

A PD-monitoring system on site has already been presented in publications as e.g. [1], [3]. Thus the complete system will only be reviewed in a brief way. Suitable sensors for continuous online measurement are e.g. ferrite cores mounted on the measuring tap of the bushings and/or in the connection of the neutral to the earth of transformers. Followed by an amplifier and an A/Dconverter, the signals can be downloaded by a personal computer, performing the signal processing. Electrical p.d. measurement on site online has two major factors reducing the achievable sensitivity. The first common disturbance in substations are the narrowband noises, caused mostly by radio stations or power electronics. The second common source of disturbances in online p.d. measurements are corona impulses and impulses of power electronics. Both of them can be rejected by digital filter algorithms, so that a sensitivity of about 700 pC is achieved [3]. Further effects reducing the sensitivity are strong electromagnetic radiation or corona, capacitive coupling of the phases, p.d. flowing over the earthed housing and a high in the transformer grounding.

Online PD-Monitoring, Transformer, Acoustic Emission Technique, Diagnostics