Showing papers by "Hydro-Québec published in 2009"

Lakes and reservoirs as regulators of carbon cycling and climate

Abstract: We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.

Development of Rule-Based Classifiers for Rapid Stability Assessment of Wide-Area Post-Disturbance Records

Abstract: The paper proposes a systematic scheme for building compact and transparent fuzzy rule-based classifiers for rapid stability assessment; the classifiers are initialized by large accurate decision trees (DTs). The approach starts by selecting strategic monitoring buses where phasor measurement units (PMUs) are placed to capture wide-area response signals in real-time operation. These measurements are processed in the time and frequency domains for extracting selected decision features such as the peak spectral density of the angle, frequency and their dot product evaluated over the grid areas. These so-called wide-area severity indices (WASI) are reliable time-varying stability indicators that form the basis of an effective classification system. Large-size DTs are used to generate initial accurate classification boundaries for decision making as early as 1 s or 2 s after fault clearing. From the DT classification boundaries, fuzzy membership functions (MFs) are developed and the corresponding fuzzy rule base is formulated parsimoniously by eliminating redundant MFs and rules using a similarity measure. The resulting fuzzy-rule classifiers are successfully tested for system-wise and area-wise contingencies based on a large database of detailed simulations of the Hydro-Quebec grid and are further confirmed on actual measurements recorded with existing wide-area measurements (WAMS).

Synthetically derived profiles for representing occupant-driven electric loads in Canadian housing

Abstract: As one objective of the International Energy Agency's Energy Conservation in Buildings and Community Systems Programme Annex 42, detailed Canadian household electrical demand profiles were created using a bottom-up approach from available inputs, including a detailed appliance set, annual consumption targets and occupancy patterns. These profiles were created for use in the simulation of residential cogeneration devices to examine the issues of system performance, efficiency and emission reduction potential. This article describes the steps taken to generate these 5-min electrical consumption profiles for three target single-family detached households – low, medium and high consumers, a comparison of the generated output with measured data from Hydro Quebec, and a demonstration of the use of the new profiles in building performance simulations of residential cogeneration devices.

Fuzzy Partitioning of a Real Power System for Dynamic Vulnerability Assessment

Abstract: Recently, the authors proposed a clustering approach based on the fuzzy C-medoid algorithm (FCMdd), for segregating large power systems into coherent electric areas centered around a representative so-called medoid-bus. This bus was shown to be a natural location for PMU in the context of wide-area measurement system (WAMS) configuration for of dynamic vulnerability assessment (DVA). The method was demonstrated on two test systems. The goal of this companion paper is to extend the approach to an actual grid (Hydro-Quebec) with more realistic characteristics in terms of geography and system dynamics. We start by developing a formulation of the coherency matrix that is recursive in time to enable online grid partitioning. The FCMdd is then implemented and compared with other statistical learning techniques. It is observed that only FCMdd is able to provide an intuitively appealing 7-clusters solution for 429-bus system. It is further demonstrated that medoids-based system-wise indices can forecast the contingencies severity under varying network configurations and loadings.

Electrochemical and Thermal Studies of Carbon-Coated LiFePO4 Cathode

Abstract: The carbon-coated LiFeP0 4 Li-ion cathode material was studied for its electrochemical and thermal performance. This electrode exhibited a reversible capacity corresponding to more than 90% of the theoretical capacity when cycled between 2.5 and 4.0 V. The material also showed good capacity retention at high powers, implying that the carbon coating improves the electronic conductivity and hence the cycling of this material. The diffusion coefficient of this material was calculated from its electrochemical impedance spectroscopy. The heat generation during charge and discharge was studied using an isothermal microcalorimeter. Thermal studies were also investigated by using a differential scanning calorimeter and an accelerating rate calorimeter, which showed that LiFePO 4 is safer than the commonly used lithium metal oxide cathodes with layered structures.

Analysis of performance of the optimized divertor in ITER

Abstract: The paper describes the results of a physics analysis of a modified divertor cassette for ITER. The issues addressed are the impact on the operational window, the effect of gas leaks through the broader gaps between the divertor cassettes and radiation power loading of different components of the cassettes. The analysis shows that the new design ensuring more flexibility for ITER operation remains acceptable within the framework of the usual trade-off between the target power loading and helium removal efficiency. The radiation load on the side walls of the cassette structures in the inter-cassette gaps is identified as a design constraint not previously considered.

Transmission line maintenance robots capable of crossing obstacles: State-of-the-art review and challenges ahead

Abstract: Power line inspection and maintenance already benefit from developments in mobile robotics. This paper presents a comprehensive review of the state of the art. It focuses on mobile robots designed to cross obstacles found on a typical transmission line while using the conductor as support for traveling. Promising areas of research and development as well as challenges that remain to be solved are discussed with a view to developing fully autonomous technologies. Maintenance tasks, including inspection and repairs, are identified as high-value applications in transmission live-line work. Conclusions are drawn from experience, and the future of mobile robotics applied to transmission line maintenance is discussed. © 2009 Wiley Periodicals, Inc.

Corrosive Sulfur Induced Failures in Oil-Filled Electrical Power Transformers and Shunt Reactors

Abstract: The nature and causes of corrosive sulfur induced failures are examined in oil-filled transformers and shunt reactors. Copper sulfide, which is formed when the corrosive sulfur in a mineral oil reacts with the copper conductors, is likely to diffuse into the paper tapes insulating the conductors. Since copper sulfide is partially conducting, the dielectric losses of the contaminated oil-impregnated-paper tapes are markedly increased; paper tapes in close proximity to the copper conductors are found to attain tan delta values > 1.0 even at room temperature. It is highly likely that thermal instabilities develop at those sites at operating temperatures, leading to increased loss currents and, ultimately, short circuits between the turns. This sequence of events is substantiated by evidence from the field, which indicates large areas of thermally degraded insulations and charred breakdown regions along the coils, the extent of which becomes more pronounced at higher operating temperatures (toward the top of the windings).

The role of hydrological model complexity and uncertainty in climate change impact assessment

Abstract: . Little quantitative knowledge is as yet available about the role of hydrological model complexity for climate change impact assessment. This study investigates and compares the varieties of different model response of three hydrological models (PROMET, Hydrotel, HSAMI), each representing a different model complexity in terms of process description, parameter space and spatial and temporal scale. The study is performed in the Ammer watershed, a 709 km2 catchment in the Bavarian alpine forelands, Germany. All models are driven and validated by a 30-year time-series (1971–2000) of observation data. It is expressed by objective functions, that all models, HSAMI and Hydrotel due to calibration, perform almost equally well for runoff simulation over the validation period. Some systematic deviances in the hydrographs and the spatial patterns of hydrologic variables are however quite distinct and thus further discussed. Virtual future climate (2071–2100) is generated by the Canadian Regional Climate Model (vers 3.7.1), driven by the Coupled Global Climate Model (vers. 2) based on an A2 emission scenario (IPCC 2007). The hydrological model performance is evaluated by flow indicators, such as flood frequency, annual 7-day and 30-day low flow and maximum seasonal flows. The modified climatic boundary conditions cause dramatic deviances in hydrologic model response. HSAMI shows tremendous overestimation of evapotranspiration, while Hydrotel and PROMET behave in comparable range. Still, their significant differences, like spatially explicit patterns of summerly water shortage or spring flood intensity, highlight the necessity to extend and quantify the uncertainty discussion in climate change impact analysis towards the remarkable effect of hydrological model complexity. It is obvious that for specific application purposes, water resources managers need to be made aware of this effect and have to take its implications into account for decision making. The paper concludes with an outlook and a proposal for future research necessities.

Corrosive sulfur effects in transformer oils and remedial procedures

Abstract: The behavior of corrosive sulfur in mineral oils is examined in terms of the failures observed in transformers, the surfaces of the copper sulfide covered conductors and degraded paper insulating tapes. The role of dissolved gas analysis (DGA) in the evaluation of the risk of copper sulfide formation is described. The degree of corrosiveness of some sulfur compounds is examined and compared using a Kraft paper wrapped-copper test (standard IEC 62535). The occurrence of DBDS as the most relevant corrosive compound is compared with the presence of other corrosive species in insulating mineral oils. A number of mitigation techniques for corrosive sulfur are described and evaluated.

Kinetics of the production of chain-end groups and methanol from the depolymerization of cellulose during the ageing of paper/oil systems. Part 1: Standard wood kraft insulation

Abstract: Recently, the existence of a relation between the rupture of 1,4-β-glycosidic bonds in the cellulose during thermal-ageing of paper/oil systems and the detection of methanol in the oil has been reported for the first time in this journal (Jalbert et al. 2007). The present study addresses the rate constants of the reaction for standard wood kraft papers, two immersed in inhibited naphthenic oil under air (paper/oil weight–volume ratio of 1:18) and one in non-inhibited paraffinic oil under nitrogen (paper/oil weight–volume ratio of 1:30). The isotherms in the range of 60–130 °C show that the initial rate of methanol production markedly increases with temperature and to a lesser extent with the moisture of the specimens (initially between 0.5 and 2.25% (w/w)), similarly to what is noted for the depolymerization through the Ekenstam’s pseudo-zero order model. The Arrhenius expression of the rate constants reveals linear relationships that confirm the dominance of a given mechanism in both cases. A very good agreement is also noted for the activation energy over the entirely paper/oil systems studied (106.9 ± 4.3 and 103.5 ± 3.7 kJ mol−1 for methanol and scissions, respectively). Furthermore, a comparison of the rate constants \( \left( {k_{{{\text{CH}}_{ 3} {\text{OH}}}} /k_{\text{scissions}} } \right) \) shows approximately constant values indicating an apparent yield for the methanol of about one-third molecule per every scission for the tests under air (0.27 ± 0.04 for Clupak HD75 and 0.37 ± 0.14 for Munksjo TH70) and even lower for the ones under N2 (0.12 ± 0.03 for Munksjo E.G.). As expected from a pseudo-zero order model, these values were shown to be consistent with a similar comparison of the amount of CH3OH and chain-end groups produced under specific time–temperature ageing conditions (168 h at 120 °C). Finally, an additional test carried out with unaged cellulose in contact with a fresh solution of methanol in oil (cellulose/oil weight–volume ratio of 1:18) shows that at equilibrium, over 58% of the species is lost from the solution due to penetration into the fibres. Such results reveal the importance of the species partitioning in establishing the true correspondence between the molecules of CH3OH produced and the scissions.

Formation and properties of C-S-H–PEG nano-structures

Abstract: Results of an investigation of the intercalation potential of polyethylene glycol (PEG) with synthetic and pre-treated C-S-H are reported. The partial intercalation of PEG molecules in the interlayer of C-S-H is discussed. The effective and strong interaction of PEG molecules with the C-S-H surface was shown using XRD, 13C CP and 29Si MAS NMR, and DTGA. The position and character of the 002 low angle XRD peak of C-S-H are affected by drying procedures and concomitant chemical treatment preceding intercalation and the reaction temperature. Recovery of the initial 002 position after severe drying and intercalation with distilled water or PEG is incomplete but is accompanied by an increase in intensity. It is inferred that the stability of C-S-H binders in concrete can be impacted by a variation in nanostructure dependent on curing temperature and use of chemical admixtures.

Investigations on some electrochemical aspects of lithium-ion ionic liquid/gel polymer battery systems

Abstract: Electrochemical and interfacial characteristics of Li-ion battery system based on LiFePO4 cathode and graphite anode with ionic liquid (IL) electrolytes have been investigated, both with and without addition of a small amount of polymer to the electrolyte. The IL electrolyte consisted of bis(fluorosulfonyl)imide (FSI) as anion and 1-ethyl-3-methyleimidazolium (EMI) or N-methyl-N-propylpyrrolidinium (Py13) as cation, and operated at ambient temperature. We reported previously that the SEI formation with IL was stabilized in the graphite anode at 80% coulombic efficiency (CE) in the first cycle, when FSI anion is used. In this work, we extend the study to the LiFePO4 cathode material. Gel polymer with IL is one part of this study. The stepwise impedance spectroscopy was used to characterize the Li/IL-Gel polymer/LiFePO4 at different states of charge. This technique revealed that the interface resistance was stabilized when the cathode is at 70% DoD (Depth of Discharge). The diffusion resistance is higher at the two extremes of discharge when monophase LiFePO4 state (0%DoD and 100%DoD) obtains. When polymer is added to the IL, interface resistance is improved with 1 wt.% but results with IL alone are not improved for the case of 5 wt.% polymer added. Good cycling life stability was obtained with Li/IL-FSI/LiFePO4 cells, with or without polymer. The first evaluation of the Li-ion cell, LiFePO4/IL-FSI-(5 wt.%) gel polymer/graphite, has shown low first CE at 68.4% but it recovers in the third cycle, to 96.5%. Some capacity fade was noticed after 30 cycles. The rate capability of the Li-ion cell shows a stable capacity until 2 C discharge rate.

Tools for the assessment of hydrological ensemble forecasts obtained by neural networks

Abstract: The increasing demand for uncertainty assessment in streamflow forecasts has drawn the hydrological community's interest toward ensemble forecasting techniques. The widespread deterministic hydrological forecasting point of view focuses to a great extent on the search for a hydrological model that would come as close as possible to “perfection” (i.e. the aim is to implement a model that produces a point forecast that is as close as possible as the observed outcome). On the other hand, ensemble forecasting departs from the deterministic point of view by avoiding the assumption that the “perfect” model exists and instead focuses on issuing a type of forecast that accounts explicitly for the uncertainty inherent to the forecasting process as a whole. In this paper, one-day-ahead hydrological ensemble forecasts obtained by stacked neural networks are presented and analysed. To do so, three simple performance assessment criteria are presented. Those criteria were originally developed in the meteorological and statistical communities to accommodate the need for a quality assessment methodology that is coherent with the probabilistic nature of ensemble weather forecasts. It will be shown that, even though the ensemble forecasts suffer from underdispersion, they outperform point forecasts.

LineScout Technology: From inspection to robotic maintenance on live transmission power lines

Abstract: Power line inspection and maintenance practices are evolving as changing market regulations, significantly increased line loading and system availability requirements put pressure on grid owners to innovate. Robotics is thus making its debut in that field. Described in previous papers as an inspection tool, Hydro-Quebec LineScout Technology is evolving into a teleoperated mobile robot capable of performing basic maintenance tasks. Programmable pan-and-tilt camera (PPTC) units were designed and implemented as the first step towards enhanced teleoperation control. LineArm, a dual end effector robotic arm, was specifically designed for work on bundled conductors. Design specifications and kinematics of these two subsystems are presented. Implemented application modules to be mounted on LineArm are also presented and their utilization is reported as a milestone in power line live maintenance. Lastly, future work and challenges in applying robotics to transmission line maintenance are briefly discussed.

Composite electrode material

Abstract: The invention relates to a composite electrode material consisting of a carbon coated complex oxide, fibrous carbon and a binder. Said material is prepared by a method which comprises co-grinding an active electrode material and fibrous carbon, and adding a binder to the co-grinded mixture to lower the viscosity of the mixture. The fibrous carbon is preferably vapor grown carbon fibers.

Comparative PD pulse burst characteristics of transformer type natural and synthetic ester fluids and mineral oils

Abstract: The partial discharge (PD) pulse burst behavior in natural and synthetic organic ester fluids and mineral oils of the type used in transformers has been examined, using simultaneous wide and narrow band measurement techniques. This permitted the determination and comparison of both the overall charge transfer of the PD pulse as well as that of the discrete PD pulses comprising the PD pulse burst in the evaluated dielectric fluids.

Overload Alleviation With Preventive-Corrective Static Security Using Fuzzy Logic

Abstract: This paper presents a concept overview of an automatic operator of electrical networks (AOEN) for real-time alleviation of component overloads and increase of system static loadability, based on state-estimator data only. The control used for this purpose is real-power generation rescheduling, although any other control input could fit the new framework. The key performance metrics are the vulnerability index of a generation unit (VIGS) and its sensitivity (SVIGS), accurately computed using a realistic ac power flow incorporating the AGC model (AGC-PF). Transmission overloads, vulnerability indices and their sensitivities with respect to generation control are translated into fuzzy-set notations to formulate, transparently, the relationships between incremental line flows and the active power output of each controllable generator. A fuzzy-rule-based system is formed to select the best controllers, their movement and step-size, so as to minimize the overall vulnerability of the generating system while eliminating overflows. The controller performance is illustrated on the IEEE 39-bus (New England) network and the three-area IEEE-RTS96 network subjected to severe line outage contingencies. A key result is that minimizing the proposed vulnerability metric in real-time results in increased substantial loadability (prevention) in addition to overload elimination (correction).

An average value model-based design of a deadbeat controller for VSC-HVDC transmission link

Abstract: The objective of this paper is to show performances of the deadbeat controller applied to a VSC-HVDC transmission link. The system studied is based on 3-level neutral point clamped (NPC) converters. The dynamic response of the VSC-HVDC is of primary importance under various operating conditions. It is also important that the converter valve currents be limited during AC disturbances in order to avoid the blocking of the converter. A deadbeat control system is designed using the average value model of the converter and then the obtained controller is used with a detailed model and the system performances are shown during change of active power and a three phase short-circuit. Simulation results for a 200MW, 50Hz, 230kV, VSC-HVDC system show that the deadbeat controller has an excellent transient response.

Seasonal Thermal Displacements of Gravity Dams Located in Northern Regions

Abstract: Seasonal temperature displacements are an important component of the total displacements recorded by pendulum measurements at gravity dams located in northern regions. A hybrid dam displacement model is presented in this paper to interpret these displacements and extrapolate the response for an extreme thermal event not yet experienced by the dam. The hybrid model uses a simplified deterministic structural dam representation with beam elements in complement to a hydrostatic seasonal time (HST) statistical displacement model. Comparisons are first established between 1D heat transfer analyses of typical gravity dam sections, and 2D finite-element (FE) analyses. Thermomechanical displacements are compared to show the validity of the proposed simplified deterministic beam model for typical dams. A case study of an actual 40 m gravity dam located in Quebec, Canada is then presented. It is shown that the deterministic model can be calibrated using the pendulum displacements and the HST model. The calibrated deterministic model is then used to extrapolate the displacement response for extreme thermal events not yet experienced by the dam. The proposed methodology represents a simple extension of the gravity method, widely used to verify gravity dam stability, as a first step to interpret recorded pendulum displacements and set appropriate warning and alarm levels on a rational basis before developing 2D and 3D thermomechanical FE deterministic dam models that require a lot of resources and expertise to be used effectively.