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pubblicazioni - Memoria

An innovative electro-optic sensor for AC and DC electric field detection: experimental results

pubblicazioni - Memoria

An innovative electro-optic sensor for AC and DC electric field detection: experimental results

La memoria descrive l’attività svolta in RSE relativa allo sviluppo e alla sperimentazione di una sonda per la misura del campo elettrico basata sull’uso di un cristallo elettro-ottico. La sonda consente di effettuare misure delle componenti radiale ed assiale del campo elettrico lungo gli isolatori compositi delle linee AT.

Composite insulators of overhead power lines have demanding request of immunity from defects both at the beginning of their life, and after long periods from their installation. Problems caused by lack of insulation can be in fact quite severe, leading in the worst cases to discharge events and consequently to possible blackouts. To prevent these faults, periodic inspection of line insulators should therefore be required. Many techniques for the in-field measurement of the insulating properties of the high voltage line insulators have been developed: the visual and acoustic detection, that in presence of electric discharge or corona effect detect the emission of IR or UV electromagnetic wave or acoustic wave, and the technique based on the measure of the electric field around the high voltage component. The visual and acoustic detections can detect only advanced state of deterioration and don’t allow to discover the initial stages of degradation. The detection of the electric field around the insulator allows to detect, preventing the discharge event, anomalous variation of the electric field profile due to internal damages. The measurement of the electric field can be done by means of electrical or optical probes. The electrical probe, due to the presence of metallic components, can modify the spatial distribution of measured electric field, moreover it has quite large dimensions and it can’t discriminate between the different components of the electric field. In this work we present an innovative optical measurement probe and the experimental results obtained on full size power line insulators. The optical technique we developed is based on an electro-optic crystal, and the probe we developed is totally dielectric. The probe does not affect the field to be measured, it is quite small, and has a linear response. The probe can perform electric field directional measurement. The sensor performances have been tested by measuring the radial and axial components of the electric field along 150kV high voltage composite insulators: the measurement is performed with the insulator carrying the line cable powered with AC high voltage and, in a second series of tests, with DC high voltage. The measurements were performed for three insulators of the same type: two with known damages in different positions and one without damages. By analyzing the variation between the field profiles of the insulators, it has been possible to detect clearly the position of the internal damages. In our knowledge, these measurement results are the first obtained on real composite insulators for the radial and axial component of the electric field both for AC and DC applied voltages. It can be noted, for DC measurements, that a change of sign of the radial component occurs when moving the sensor along a line parallel to the axis of the insulator. The experimental measurement shown that the proposed electro-optic sensor can be used to detect damages inside the high voltage insulators. The same sensor can detect as well the damages on different types of high voltage components.

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