Werle, P: Erfassung und Evaluierung von Teilenladungen

eine effiziente Unterdrückung von vor Ort auftretenden Störsignalen erlaubt, wobei kontinuierliche Störsignale durch Frequenzsperrfilter im Frequenzbereich sowie durch Wavelet-Filter unterdrückt werden, während stochastisch entstehende impulsförmige Störungen durch eine Ortung der TE-Quelle zu separieren sind. Das Ortungsprinzip beruht dabei auf der gleichzeitigen Messung der TE-Signale an Durchführung und Sternpunkt und deren Zurückberechnung an den Entstehungsort mittels der Teilübertragungsfunktionen der Transformatorwicklungen, wodurch der TE-Signalverlauf am Entstehungsort berücksichtigt werden kann, was eine genauere Ladungsbestimmung als mit anderen breitbandigen Verfahren ermöglicht. Dies wurde an Messungen von unterschiedlichen TE-Signalen an einem Verteiltransformator im Labor nachgewiesen, wobei durch den Einsatz des Verfahrens an verschiedenen Transformatoren im Betrieb die Eignung des Systems verifiziert und optimiert werden konnte, so dass inzwischen eine partielle markttechnische Umsetzung des Systems erfolgte.




Abstract

Detection and Evaluation of Partial Discharges on Transformers using Innovative Sensor Technologies and Enhanced Digital Signal Processing Tools

Key-words:Power transformers - dry-type transformers - diagnostics partial discharges - transfer function - monitoring

Transformers belong to the most important and expensive components in energy transmission and supply systems wherefore condition assessment methods becomes increasingly essential in order to improve their reliability and profitability. Both is with regard to the fact that the mayor part of the transformers have reached or respectively exceeded their design age as well as due to the liberalisation of the energy supply market indispensable. Partial discharge (PD) measurements represent an established method for assessing the insulation condition of high voltage apparatus, thus in this thesis new methods for the detection and evaluation of PD signals are introduced especially for the use on dry type and paper-liquid insulated power transformers.
For dry type transformers insulated by epoxy resin a multi-PD-decoupling system has been developed, which uses a new sensor technology in order to detect the PD signals on various points on a transformer coil, thus allowing a PD localisation and a more precise determination of the apparent charge of a PD pulse in comparison to conventional techniques. Furthermore an online protection system has been realised, which uses a fibre optic sensor for the recognition of defects inside the solid insulation initiated by PD activity, wherefore this system has been installed in the meantime on more than 50 dry type power transformers and could prevent some units from serious damages.
For paper-liquid insulated transformers a PD detection and analysing system is introduced, which allows an efficient suppression of noises as they appear during measurements on-site due to the use of an improved signal decoupling and optical signal transmission combined with self adjusting digital filters. Continuous noises are separated by frequency rejection filters in the frequency domain and wavelet-filters, while stochastically appearing noise pulses can be suppressed by an impulse localisation. Therefore the PD signals are measured simultaneously at the bushing and at the neutral and mapped to their origins using the sectional winding transfer functions of the transformer coils. This visualises the PD shape at their source, thus a more precise determination of the apparent charge than with any other method using a wideband PD evaluation is possible, which has been verified on a distribution transformer in the laboratory. This system has been improved during various PD measurements on transformers in operation leading in the meanwhile to a partial commercialisation of the system.