''Listening instrument'' for high-voltage cables

Walter Hansen, EFI is looking for faults using the new instrument.

The internal discharges that sometimes occur in high-voltage cables may break down their insulation between high-tension components and earth. Breakdowns of this sort can leave whole towns or villages without electrisity.

The instrument that can detect internal partial discharges was originally developed for use in gas-insulated systems. However, tests showed that it was as least as suitable for detecting internal discharges in the end terminations of high-voltage cables.

When measurements are made in a power station, for example, the door to the high-tension cell is opened and a fibre-glass rod, that acts as an acoustic wave-guide, is placed against the end-connector of the high-voltage cable. The rod also functions as an insulator between the high voltage and the acoustic sensor (microphone) that is safely earthed at the other end. The acoustic signals are transformed into electrical signals in the sensor. These are recorded and analysed by the instrument itself ­ a portable unit with a display. The instrument also comprises a small loudspeaker which emits a crackling noise if there are discharges. The instrument, which measures only 25 x 15 x 31 cm and weighs 6 kg, is about to be manufactured and marketed by TransiNor AS in Trondheim. Potential users are power stations all over the country.