Hydro-Québec

About: Hydro-Québec is a government organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Electric power system & Dielectric. The organization has 2596 authors who have published 4433 publications receiving 100878 citations.

Capacitance calculations for some basic high voltage electrode configurations

Abstract: Calculation of the capacitance to ground, as well as of the capacitance between objects of various shapes is a problem occurring frequently in high voltage engineering. Simple methods do not exist, however, for such calculations even in the case of some basic electrode configurations. Although general purpose computer programs may have been developed for most of the configurations, their availability is rather limited, and the data preparation often cumbersome. Accurate computer calculations of the capacitance to ground have been made for a large number of electrode configurations. The results are presented graphically in a normalized form, and should permit a rapid and precise determination of capacitances for most practical electrode arrangements. Furthermore, some simple equations have been developed which permit an approximate, but often sufficiently accurate, evaluation of the capacitances by hand calculations. It is believed that both the accurate graphs and the simple equations would be of great practical value, especially to high voltage engineers.

Understanding ethanol versus methanol formation from insulating paper in power transformers

Abstract: The life of an electrical transformer is mainly determined by that of its cellulosic solid insulation. The analysis of the chemical markers of cellulose degradation dissolved in oil is a simple and economical way to indirectly characterize the insulating paper. Methanol, a marker that is intimately linked to the rupturing of 1,4-β-glycosidic bonds of cellulose, has been observed together with ethanol during laboratory ageing experiments. Regardless of the simulated ageing conditions (temperature, humidity, air), the ratio of methanol to ethanol concentration is always higher than one (unity). However, in approximately 10 % of transformer oil samples, the ethanol generation is higher than that of methanol. In this study, thermal degradation by pyrolysis is coupled with gas chromatography/mass spectrometry to assess the volatile by-products generated at high temperatures with emphasis on methanol/ethanol generation. Some cellulose model compounds were also pyrolyzed and thermally aged in oil. The results showed that the generation of ethanol from paper pyrolysis is always smaller than for methanol, but it only occurs at temperatures higher than 300 °C. However, thermal ageing of levoglucosan in oil generates a massive amount of ethanol compared to methanol regardless of the conditions (temperature, humidity, air, nitrogen, acidity). The hypothesis that ethanol is a by-product of cellulose degradation through levoglucosan as an intermediary in power transformers is proposed. The presence of ethanol during transformer oil analysis is of high interest because it can be related to a thermal fault or hot spot within the solid insulation.

Simultaneous ultrawide and narrowband detection of PD pulses in dielectric liquids

Abstract: Simultaneous narrow band (300 kHz) and wide band (500 MHz) measurements were carried out to obtain estimates of the apparent charge transfer associated with discrete isolated discharge pulses and discharge pulse bursts, which are observed to occur in dielectric liquids when wide band detection systems are utilized. The integrated apparent charge transfers determined with the narrow band system ranged from 12 to 95 pC, which represents typically the lower range of values normally encountered with PD activity in dielectric liquid-filled or impregnated equipment. While the discharge phenomena in perfluoro polyether liquids was found to be typified by sporadic appearances of single isolated pulses involving charge transfers between 33 and 38 pC, the discharge events in mineral oils assumed most frequently the form of pulse bursts, displaying the usual pulse sequences of quasi-ascending amplitudes; the overall integrated apparent charge transfer of the observed pulse bursts extended commonly from 12 to 16 pC. The charge release, occurring with the first (initiating) smallest discharge pulse within the pulse bursts, was estimated to be of the order of /spl sim/1 pC.

Vibro-acoustic signature treatment process in high-voltage electromechanical switching system

Abstract: In the present method and apparatus for processing a vibro-acoustic signal (1) emitted by a high-voltage switching system, the vibro-acoustic signal (1) is converted into a digital signal (3). The digital signal (3) is rectified and the resulting rectified signal (5) is applied to a convolutional filter with a spectral window (6) to produce a smoothed signal (7). The smoothed signal (7) is decimated to produce a decimated signal (9) representing an envelope of the vibro-acoustic signal (1). A time realignment of the decimated signal (9) is carried out with respect to a reference signature (13A) to produce a realigned signal (11). Time deviation values generate an alarm if they exceed a limit threshold. The realigned signal (11) is added as a factor of means providing a reference signature (13A) and an actualized signature (13B). Variances (15A, 15B) of the realigned signal (11) are calculated with respect to the reference and actualized signatures (13A, 13B). The realigned signal (11) is compared with the actualized and reference signatures (13A, 13B) to detect a gradual behavior change or a sudden defect, taking the variances (15A, 15B) into consideration.

Iteratively reweighted least squares for maximum likelihood identification of synchronous machine parameters from on-line tests

Abstract: This paper presents a new approach for the statistical identification of synchronous-machine parameters from on-line test data that were recorded on a 202 MVA hydro-generator at Hydro-Quebec's La Grande 3 generating station. Data processing is performed to remove harmonics in noise-corrupted measurements. The time-domain parameter identification is carried out by means of our proposed maximum-likelihood estimation method, also called the iteratively reweighted least-squares algorithm. A comparison of the results with the ordinary weighted least-squares estimation, which is equivalent to the maximum-likelihood estimation only when the noise is white, shows the superiority of the proposed method. This procedure appears more convenient than previous schemes for parameter identification of the synchronous-machine linear equivalent-circuits, especially when the noise statistics are poorly known.