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.

Distribution transformer overloading capability under cold-load pickup conditions

Abstract: Greater use of electric heating in residential areas in North America has led to the appearance of a new type of thermal stress resulting from service restoration following a power outage This loading condition, known as cold-load pickup, is simulated on a sample of 18 distribution transformers by applying overloads up to three times the rated current at ambient temperatures as low as -40 degrees C The data gathered is used to develop a thermal model representing the transient behavior of distribution transformers The results are then generalized to produce a loading guide for evaluation of maximum hot-spot temperatures and loss of life under given cold-load pickup conditions >

Update on IEC 61000-3-6: Harmonic Emission Limits for Customers Connected to MV, HV, and EHV

Abstract: IEC Standards for controlling harmonic distortion levels on the power system fall into two categories. IEC 61000-3-2 and 61000-3-12 outline limits for harmonic emissions from individual equipment. These standards apply for equipment up to 75 amps (on 230 volt systems). IEC 61000-3-6 outlines procedures for evaluating harmonic emissions from facilities that are connected to MV, HV, and EHV systems. This standard is currently undergoing revision. This summary paper and the associated presentation describe important aspects of the 61000-3-6 standard for comparison with IEEE harmonic standards

PD pulse burst characteristics of transformer oils

Abstract: Partial Discharge (PD) characteristics of four typical transformer oils, having respective viscosities of 3.5, 9.1, 13.0, 18.3 cSt at 40/spl deg/C, were examined under ac conditions, using a needle-to-plane electrode system. Wide and narrow bandwidth measurements were carried out to determine simultaneously the apparent charge transfers associated with the overall PD pulse bursts in the oil as well as that of the individual discrete PD pulses within the PD pulse bursts themselves. Based on the apparent charge transfer value, the size or depth of the PD initiating microcavities in the field direction within the oils, producing the first detected discrete PD pulse, were estimated to be in the order of 2 /spl mu/m. The recurrence rate of the PD pulse bursts was found to increase with voltage above the PD inception voltage; this increase was accompanied by both an increase in number of discrete PD pulses and their amplitude within the pulse burst itself. These increases were reflected by a substantial rise in the apparent charge transfer per PD pulse burst. The charge transfer levels of the PD pulse bursts associated with the highly pressurized gas microcavities were of the same order of magnitude as those produced within the normally much larger macroscopic cavities that exist under atmospheric pressure in conventional oil-impregnated insulating systems of power transformers.

Dams have varying impacts on fish communities across latitudes: a quantitative synthesis

Abstract: Dams are recognised to impact aquatic biodiversity, but the effects and conclusions diverge across studies and locations. By using a meta-analytical approach, we quantified the effects of impoundment on fish communities distributed across three large biomes. The impacts of dams on richness and diversity differed across biomes, with significant declines in the tropics, lower amplitude but similar directional changes in temperate regions, and no changes in boreal regions. Our analyses showed that non-native species increased significantly in tropical and temperate regulated rivers, but not in boreal rivers. In contrast, temporal trajectories in fish assemblage metrics were common across regions, with all biomes showing an increase in mean trophic level position and in the proportion of generalist species after impoundment. Such changes in fish assemblages may affect food web stability and merit closer study. Across the literature examined, predominant mechanisms that render fish assemblages susceptible to impacts from dams were: (1) the transformation of the lotic environment into a lentic environment; (2) habitat fragmentation and (3) the introduction of non-native species. Collectively, our results highlight that an understanding of the regional context and a suite of community metrics are needed to make robust predictions about how fish will respond to river impoundments.