Showing papers by "Ray Bartnikas published in 2008"

Corrosive Sulfur in Insulating Oils: Its Detection and Correlated Power Apparatus Failures

Abstract: Contamination of paper tapes by corrosive sulfur in insulating oils may cause shorting faults between turns. Typically, this occurs at higher temperature in the upper portions of the windings of shunt reactors and power transformers. In many of the tested oils, high amounts of dibenzyl-disulfide (DBDS) were found.

On-line detection and measurement of partial discharge signals in a noisy environment

Abstract: In extracting partial discharge (PD) signals embedded in excessive noise, the need for an online and automated tool becomes a crucial necessity One of the recent approaches that have gained some acceptance within the research arena is the Wavelet multi- resolution analysis (WMRA) However selecting an accurate mother wavelet, defining dynamic threshold values and identifying the resolution levels to be considered in the PD extraction from the noise are still challenging tasks This paper proposes a novel wavelet-based technique for extracting PD signals embedded in high noise levels The proposed technique enhances the WMRA by decomposing the noisy data into different resolution levels while sliding it into Kaiser's window Only the maximum expansion coefficients at each resolution level are used in de-noising and measuring the extracted PD signal A small set of coefficients is used in the monitoring process without assigning threshold values or performing signal reconstruction The proposed monitoring technique has been applied to a laboratory data as well as to a simulated PD pulses embedded in a collected laboratory noise

De-noising of partial discharge signal using eigen-decomposition technique

Abstract: The Rogowski coil method for the measurements and detection of PD signals represents a cost effective and practical way to measure PD signals in electrical power apparatus; however it is subject to excessive noise pick-up because of its inductive nature. This paper discusses the implementation of a de-noising algorithm using eigen-decomposition approach, which can be utilized in order to minimize the extraneous noise encountered with on-line tests in the field. The proposed algorithm possesses the inherent advantage of decomposing the signal space and separates it from the noise subspaces. Results discussed in the paper demonstrate the performance of the proposed technique for both simulated and experimental PD signals.

Particle identification in terms of acoustic partial discharge measurements in transformer oils

Abstract: Acoustic measurements of partial discharge (PD) are employed to classify particles in transformer mineral oil according to material and size. Wavelet multi-resolution analysis data of the acoustic signals together with higher order statistics of the particle intercollision times and magnitudes comprise the input features to a Support Vector Machine (SVM) classifier. The training and validation measurement data, which are contaminated by time varying noise, are first filtered using wavelet decomposition. Results indicate that the SVM algorithm with the selected features provides a remarkably high success rate when classifying particles by size and material type. A potentially significant conclusion is that acoustic measurements alone are by themselves effective in classifying discharged particles in terms of the foregoing selected features. The proposed algorithm can be employed to enhance quality control procedures based on acoustic measurements of partial discharge.

In Service Reduction of Corrosive Sulfur Compounds in Insulating Mineral Oils

Abstract: Removal of dibenzyl-disulfide (DBDS) from a mineral oil of an in-service transformer was found to greatly reduce the overall corrosive sulfur content of the oil. In addition, a very significant improvement was also obtained in the acidity, surface tension, and to some degree in the dielectric loss characteristics of the mineral oil.

PD pulse burst behavior of a transformer type synthetic organic ester fluid

Abstract: The partial discharge (PD) pulse burst characteristics of a transformer type synthetic organic ester fluid were compared with those of an equivalent transformer type mineral oil. Wide and narrow bandwidth measurements were carried out to determine simultaneously the apparent charge transfers associated with the overall PD pulse burst as well as that of the individual discrete pulses within the PD pulse burst. The PD pulse burst behavior was found to be similar in both insulating liquids. The discharge cavity formation times ranged from 0.5 to 1.5 mus, while the charge transfers associated with the PD pulse bursts in the liquids were found to extend from approximately 5 to 30 pC.

Partial discharge inception voltage measurements in dielectric liquids

Abstract: A test procedure is proposed for the measurement of the partial discharge inception voltage (PDIV) in dielectric liquids. The antecedent IEC point-to-sphere test cell arrangement is replaced with that of a point-to-plane. A dual ultrawide-narrow bandwidth PD detection system is employed, which permits to distinguish the PD pulse-burst discharges that occur in liquid dielectrics from the normal PD discharges that characterize stable voids occluded within solid-liquid insulating systems.