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Recent progress in the development of ultrasonic fibre-optic sensors for detecting acoustic emission from partial discharge in elastomeric insulations is presented. These sensors are an important part of a proposed comprehensive scheme for the fibre-optic monitoring of cable accessories. After specifying the underlying design goals the improved fibre-optic sensor design is outlined. It is experimentally shown that it offers about ten-fold improvement over a previously investigated resonant cantilever-type design in terms of detection limit, making it competitive with conventional piezoelectric transducers, however with the added compatibility with strong electrical fields and electromagnetically noisy environments.
In high-voltage facilities of power stations and transmission networks, discharge activities leading to catastrophic failure can occur. Early detection of partial discharges (PD) in polymeric insulations of HV cable terminations and joints is therefore increasingly important. This paper describes a monitoring methodology to detect PD activity in silicone elastomer by two independent fibre-optic sensor types. Fluorescent fibre-based sensors are sensitive to plasma optical emission already at the onset of PD while an acoustic fibre-optic sensor responds to acoustic emission from the PD during its progression. The sensitivities of both sensor types are compared, and it is demonstrated that they provide complementary information for fibre-optic sensor-based monitoring of high-voltage cable accessories.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Konventionelle elektrische Verfahren zur Erfassung von Teilentladungen (TE) in hochspannungstechnischen Bauteilen und Betriebsmitteln erfordern elektromagnetisch ungestörte Messbedingungen und sind für die Überprüfung von Anla-gen während des laufenden Betriebs nicht unproblematisch. Daher werden für Prüfung und Überwachung im Feld zu-nehmend unkonventionelle elektromagnetische (HF, VHF, UHF) und akustische Detektionsverfahren eingesetzt. Wegen ihrer prinzipiellen Immunität gegen elektromagnetische Störungen sind darüber hinaus faseroptische Verfahren der TE-Detektion in Erprobung. Im vorliegenden Beitrag werden zwei Typen akustisch-faseroptischer Sensoren (a-FOS) vorgestellt und auf ihre Eignung untersucht, Teilentladungen in elastomeren Isolierkörpern, wie etwa Silikon-Feldsteuerelementen von Kabelgarnituren, zu detektieren. Die hier präsentierten Laborergebnisse zeigen, dass die zur Detektion von TE mit kritischer Intensität (z.B. in Kabelgarnituren) notwendige Empfindlichkeit erreicht werden kann. Darauf basierend wird das Potential der faseroptisch-akustischen Detektion von TE in der hochspannungstechnischen Zustandsüberwachung allein und in Kombination mit fasergekoppelten fluoreszenzoptischen Sensoren diskutiert.
Fibre-optic acoustic detection of damage processes in elastomeric insulation under AC and DC stress
(2013)
Fibre-optic acoustic detection of damage processes in elastomeric insulation under AC and DC stress
(2013)
We present a demodulation method that partially compensates for the nonlinear and random transfer function of fiber-optic direct detection coherent Rayleigh optical time-domain reflectometry (C-OTDR). Specifically, the proposed method is shown to improve the detection of small amplitude, high frequency dynamic optical fiber strain as it occurs in acoustic emission sensing. The method is applicable provided that the dynamic fiber strain to be sensed is known to affect a longer section of sensing fiber in a spatially homogeneous way. It is shown that this knowledge can be used to extract more quantitative information from the measured C-OTDR signal by averaging signal components from the affected fiber section in a suitable and efficient way. The theoretical basis of the method is developed and supporting experimental results are presented.
New sensors for the detection of partial discharges (PDs) in high-voltage (HV) cable accessories are being de-veloped consisting of a fluorescent polymer optical fiber (F-POF) as sensing element. Depending on the fiber material F-POFs can be attached to and even integrated into the translucent silicone rubber insulation of HV cable terminations. As the embedment into the insulation material plays an important role, the sensor should not weaken the dielectric strength of the insulation material and should not be the origin of PD incidents. A sensor consisting of a commercial F-POF has been tested in the high-voltage lab regarding its PD detection ability un-der AC in comparison to a conventional electrical sensor. New silicone rubber F-POF (Si-F-POF) fiber models functionalized with coumarin dyes have been produced. The optical properties of these dye functionalized silox-anes are presented. These potential sensor fibers are highly flexible and might be embeddable at medium to high-voltage level. An additional way to further improve the level of PD light detection is to modify the translucent type of silicone rubber used in HV cable accessories in terms of optical transparency. In this context we present our first results of the optical and mechanical properties of new elastomeric transparent silicone materials specif-ically designed for the application as HV insulation materials in stress cones.
We propose the application of Distributed Acoustic Sensing (DAS) based on Rayleigh Coherent Optical Time-Domain Reflectometry (C-OTDR) to unconventional sensing tasks in industrial condition monitoring. As examples we present results on the way to fibre-optic remote sensing of dielectric damage processes in high voltage cable joints as well as to condition monitoring of passive rollers in large industrial belt conveyor systems.