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.

Effect of physico-chemical degradation of epoxy resin on partial discharge behavior

Abstract: Epoxy resin coated electrode specimens were subjected to partial discharges (PD) in air at twice the discharge inception voltage for durations ranging to 5000 h. The PD behavior was characterized by a transition from initially large pulse type discharges (- 200 to 300 pC) to either small pulse (- 1 pC), pseudoglow, glow discharge, or a combination thereof. Although these different forms of discharges were capable of occurring simultaneously, each type tended to prevail over certain periods of the exposure time. The physical and chemical nature of the degradation products formed on the surfaces of the epoxy resin also varied accordingly, indicating that each discrete form of discharge exerts its particular effect on the overall degradation process. Droplet formation on the central portion of the epoxy surfaces typified the large pulse discharge regime, whilst crystals formed within the transition region over which small discharge pulses (- 1 pC) were usually superimposed upon a continuous glow (pseudoglow and true glow regime). The droplets were identified as being partially comprised of a mixture of acids, mainly formic, glycolic, glyoxalic and nitric acids, whilst the crystals consisted of hydrated oxalic acid. Since similar results were obtained with discharges in both air and nitrogen, the effects of gas phase reactions on the PD activity would appear to be only of secondary importance compared to the reactions taking place on the surface of the epoxy resin. Since the test cell design did not allow any pressure variation within the discharge gap, the observed discharge transition cannot be attributed to pressure changes such as may take place within occluded cavities. Nevertheless, the transition observed here is similar to what is found with actual stator bar type insulation, suggesting that pronounced chemical and physical modifications on the surface of the physical cavity inclusions in the bar insulation may account for the characteristic PD behavior observed as a function of time.

Three-transfer-function approach for building phenomenological models of synchronous machines

Abstract: The established practice of using only two transfer functions when modelling the d-axis of a synchronous machine at rest is physically questionable since it leads, from the network theory point of view, to ambiguous equivalent circuit realisations. The paper provides analytical and experimental evidence for the claim that a triple transfer function (3TF) parameterisation is the only one general enough to cope with both stator and rotor voltage perturbations, thus broadening the range of physical phenomena the model can account for. It is proposed that the third transfer function can be conveniently chosen from three closely related impedance operators, only two of which are classical. Using standstill frequency response test data from the Ontario Hydro's Lambton generator, it is shown that, for a given number of damper windings (3, 5, or 6), at least one equivalent circuit exists capable of accurately modelling the stator input inductance Ld(s) and the short-circuit stator to rotor transfer function sG(s), but failing dramatically to fit the third transfer function, i.e. the stator to field transfer inductance with field open Lafo(s). Only the 3TF approach consistently leads to equivalent circuits with definite phenomenological significance, thus enhancing the understanding of machine behaviour as affected by damper-cage design and excitation system.

Influence of particle size on the correlation between shear wave velocity and cone tip resistance

Abstract: The construction of the Peribonka dam involved deep compaction of its foundation using vibroflotation and dynamic compaction. Surface wave testing was used, in addition to classical tests (cone pen...

High Rate and Long Cycle Life of a CNT/rGO/Si Nanoparticle Composite Anode for Lithium-Ion Batteries

Abstract: Si nanoparticle (Si-NP) composite anode with high rate and long cycle life is an attractive anode material for lithium-ion battery (LIB) in hybrid electric vehicle (HEV)/pure electric vehicle (PEV). In this work, a carbon nanotube (CNT)/reduced graphene oxide (rGO)/Si nanoparticle composite with alternated structure as Li-ion battery anode is prepared. In this structure, rGO completely wraps the entire Si/CNT networks by different layers and CNT networks provide fast electron transport pathways with reduced solid-state diffusion, so that the stable solid-electrolyte interphase layer can form on the whole surface of the matrix instead of on single Si nanoparticle, which ensure the high cycle stability to achieve the excellent cycle performance. As a result, the CNT/rGO/Si-NP anode exhibits high performances with long cycle life (≈455 mAh g−1 at 15 A g−1 after 2000 cycles), high specific charge capacity (≈2250 mAh g−1 at 0.2 A g−1, ≈650 mAh g−1 at 15 A g−1), and fast charge/discharge rates (up to 16 A g−1). This nanostructure anode with facile and low-cost synthesis method, as well as excellent electrochemical performances, makes it attractive for the long life cycles at high rate of the next generation LIB applications in HEV/PEV.

A comment concerning the rise times of partial discharge pulses

Abstract: The influence of the discharge mechanism upon the rise time of partial discharge pulses is examined. In contrast to the long rise times characterizing the discharge pulses generated by glow discharges, spark discharges exhibit typically short rise times and large magnitude pulses. The occurrence of the latter is favoured by cavities wherein there is a paucity of free electrons that are necessary for electron avalanche formation. As a consequence, breakdowns across these cavities occur under overvoltage conditions, thus leading to space charge formation and photoemission at the cathode; this results in a rapid development of constricted spark-type breakdown channels. The question of detectability of short and long rise time pulses, utilizing PD detectors having different bandwidths, is considered both in the proximity to, as well as far removed from, the discharge sites.