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- Acoustic emission (4)
- Partial discharge (4)
- Silicone elastomer (4)
- High voltage cable accessories (3)
- Fibre-optic condition monitoring (2)
- Monitoring (2)
- Stress cone (2)
- AC dielectric strength (1)
- Acoustic sensors (1)
- Breakdown strength (1)
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Sensitive partial discharge (PD) measurements on HV/EHV cable systems are usually based on electrical or electromagnetic PD detection. Unfortunately, interferences may significantly reduce sensitivity, especially in on-site after-installation testing and, even more, in on-line PD monitoring. This paper deals with optical PD detection, which is absolutely immune to any kind of electromagnetic interference. Optical PD detection necessarily requires transparent or translucent insulation systems to be applicable. Stress cone elements for HV/EHV cable accessories meet the requirements for optical PD detection, if made from transparent silicone elastomers.
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.
Fibre-optic acoustic detection of damage processes in elastomeric insulation under AC and DC stress
(2013)
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.
Fibre-optic sensors for early damage detection in plastic insulations of high-voltage facilities
(2011)
Fibre-optic sensors (FOS) have great potential as online damage detectors when integrated in HV accessories. Among their well-known use as temperature and strain sensors, there are some more opportunities of use, e. g. they can intimately be embedded in polymeric insulations of HV cable terminations and joints to detect and monitor partial discharges right at the location of their origin. Two FOS types for early PD detection were investigated: an embeddable fibre-optic acoustic sensor to measure acoustlc waves in polymeric insulations generated by PDs, and a fluorescent optical fibre to detect first optical effects during ionization processes in the insulation material. The paper descrlbes these methods, related monitoring Problems and shows first test results.
Partial discharge in elastomeric high voltage insulations is a major reason for device failure. The special challenges of the high voltage environment limit the use of conventional acoustic emission sensors. Fibre-optic sensors can cope with these challenges thanks to their optical sensing principle and the use of all-dielectric materials. In this contribution, improvements to a previously introduced design of ultrasonic fibre-optic acoustic partial discharge sensors for elastomeric insulations are presented. The improved performance of fibre-optic acoustic sensors in detecting AC partial discharge is demonstrated. Furthermore, their ability to detect low-level damage processes in elastomeric insulation under DC dielectric stress is shown to outperform the highly sensitive electrical detection method.
Optical methods and monitoring systems for the PD detection in GIS, GIL and oil-immersed type transformers have been demonstrated. Very recently these methods have been extended to the detection of PDs in solid insulation materials of cable accessories. This novel application in high-voltage (HV) cable terminations consists of integrated fiber-optic sensor which requires transparent insulation materials. Therefore, transparent silicone rubbers are considered as replacement material for currently used opaque elastomeric insulation material in stress cones of HV cable accessories. For this purpose a preliminary study on the long-term stability of two commercially available fully transparent silicone rubbers was performed. Accelerated thermal aging tests were carried out for 4 hours up to 100 hours at 200 °C under a normal air atmosphere and normal atmospheric pressure. The impact of thermal aging on the AC dielectric strength of the silicone samples was investigated and additionally the optical transmittance was determined using UV-Vis spectrophotometer. The investigation indicated that the dielectric strength value of the silicone samples was seriously reduced for long-term exposures to elevated temperatures. In addition, the UV-visible transmittance of thermally aged silicone samples was also decreased. The influence of these phenomena must be taken into account for the design of HV insulation materials, particularly under extremely high temperature operating conditions.
The mechanical and electrical properties of new transparent silicone materials modified with two fluorescent dyes were investigated by measuring stress-strain behaviour, electrical breakdown strength, capacity and dissipation factor, before and after thermal ageing, as well as electrical and optical partial discharges.
Mechanical properties of the new materials are comparable to the reference and the addition of dyes stabilises them against thermal ageing. All materials are equivalent in terms of breakdown strength and capacity. The added value of transparency and fluorescence make them suitable materials for novel diagnostic applications in HV cable accessories and insulators.
Wir demonstrieren die Machbarkeit rückwirkungsfrei integrierter optischer Teilentladungssensorik für Aufschiebeelemente aus Silikonelastomer zur Verwendung in Kabelgarnituren. Zu diesem Zweck wurden sowohl ein Funktionsmodell eines optisch transparenten Silikon-Kabelendverschlusses mit integriertem Silikon-Lichtwellenleitersensor als auch ein rein optisches TE-Messsystem auf Basis von zwei Einzelphotonendetektoren und einer Koinzidenzschaltung (PD-COP) entwickelt, die hier vorgestellt werden. Die Leistungsfähigkeit und Stärken der optischen TE-Messtechnik zeigen sich sowohl in Kombination mit der elektrischen Messtechnik, als auch bei alleinigem Einsatz.
Partial discharge in polymeric insulation of high voltage equipment causes cumulative damage that progressively deteriorates the insulation, leading to eventual failure. The electrical detection of related discharge current pulses may be challenged by electromagnetic interference from the environment. In such situations the detection of acoustic emission from partial discharge can greatly enhance its detectability, especially when electromagnetically immune fiber-optic acoustic sensors are used. During experiments involving such fiber-optic sensors that were specifically designed for the detection of partial discharge in elastomeric insulation, an unexpected type of acoustic emission was observed in silicone elastomer specimens with tip–plate electrode configurations and under DC electrical stress. We present and discuss experimental results that indicate space charge injection and subsequent spontaneous dynamical processes as the source of the detected acoustic emission. We use sensitive conventional partial discharge measurement instrumentation to show that the apparent acoustic efficiency of the processes leading to the observed acoustic emission is very high. Acoustic emission triggered by discharge events with individual apparent charge values of only a few femtocoulombs could be detected.
Faseroptische Sensorsysteme bieten heute die Möglichkeit des Online-Monitorings von sensiblen, für die Energieversorgung wichtigen Betriebsmitteln. Insbesondere Hochenergiekabel, wie diese sowohl im Offshore- als auch im Onshorebereich eingesetzt werden, sind prädestiniert für eine zustandsorientierte Überwachung. Gerade Hochspannungshochenergiekabel sind Betriebsmittel, die im Falle eines Ausfalls durch Schäden mit hohen Reparatur- und Folgekosten verbunden sind. Mit dem Einsatz von faseroptischen Sensoren sind mechanische Einflüsse wie Vibrationen z. B. verursacht durch Ankerfall, Temperaturhotspots oder auch Teilentladungsaktivitäten an dezidierten vulnerablen Stellen wie Kabelendverschlüssen oder –muffen über längere Kabelstrecken detektierbar. Der Einsatz von im Rahmen des Verbundprojekts Monalisa entwickelter faseroptischer Diagnosetechnik in Verbindung mit faseroptischen Sensoren wird hier aufgezeigt.
Verteilte faseroptische Sensorik eignet sich sehr gut für eine Zustands- und Gefährdungsüberwachung von ausgedehnten Hochspannungskabelinstallationen. Basierend auf der Messung von verschiedenen faseroptischen Rückstreueffekten in der Sensorfaser lassen sich ortsaufgelöste Profile von Messgrößen wie Temperatur, Dehnung oder Vibrationen erzielen.
Hier demonstrieren wir die Leistungsfähigkeit verschiedener faseroptischer Sensorikansätze bezüglich dieser Größen anhand von Experimenten u.a. an einem Mittelspannungskabel. Des Weiteren zeigen wir, wie die Verwendung von verschiedenen Sensorkabeltypen mit unterschiedlicher Applikation auf der Kabeloberfläche die Messergebnisse bei einem Biegeversuch beeinflussen und schlussfolgern damit auf die für die Einbettung in Kabeln geeigneten Sensoren.