Showing papers by "Hydro-Québec published in 2010"

A Fuzzy Rule-Based Approach for Islanding Detection in Distributed Generation

Abstract: The proposed method develops a fuzzy rule-based classifier that was tested using features for islanding detection in distributed generation. In the developed technique, the initial classification boundaries are found out by using the decision tree (DT). From the DT classification boundaries, the fuzzy membership functions (MFs) are developed and the corresponding rule base is formulated for islanding detection. But some of the fuzzy MFs are merged based upon similarity the measure for reducing the fuzzy MFs and simplifying the fuzzy rule base to make it more transparent. The developed fuzzy rule-based classifier is tested using features with noise up to a signal-to-noise ratio of 20 dB and provides classification results without misdetection, which shows the robustness of the proposed approach for islanding detection for distributed generations in the distribution network.

Catastrophe Predictors From Ensemble Decision-Tree Learning of Wide-Area Severity Indices

Abstract: Catastrophe precursors are essential prerequisites for response-based remedial action schemes, at both the protective and the operator levels In this paper, wide-area-severity indices (WASI) derived from PMU measurements serve as the basis for building fast catastrophe predictors using random-forest (RF) learning Given the randomness in the ensemble of decision trees (DTs) stacked in the RF model, it can provide at the recall stage not only an early assessment of the stable/unstable status of an ongoing contingency but also a probability outcome which quantifies the confidence level of the decision This methodology, which to the best of our knowledge is new to the dynamic security assessment (DSA) of power systems, is also very effective in evaluating the importance of and interaction among the various WASI input features Our research unexpectedly showed that the ensemble of trees in the RF is very robust in the presence of small changes in the training data and generalize across widely different network dynamics Thus, the same RF performed very well on a large database with more than 60 000 instances from a test system (10%) and an actual (90%) system combined One such a general RF (with 210 trees) boosted the reliability of a 9-cycle catastrophe predictor to 999%, compared to only 70% when a single conventionally trained DT is used

Fabrication and properties of mechanically milled alumina/aluminum nanocomposites

Abstract: The reinforcement agglomeration in nanocomposites is a key issue that needs to be solved in order to fully benefit of the gain in strength and ductility associated with the decrease in reinforcement size from microscale to nanoscale. In this study, mechanical milling has been used successfully to disperse nanometric alumina (n-Al 2 O 3 ) in an aluminum matrix. Al 2 O 3 /Al nanocomposite powders have been produced for various alumina sizes and concentrations. The 10 vol% n-Al 2 O 3 /Al powders display hardness values near five times higher than pure unmilled Al. A decrease in the Al 2 O 3 particle size from 400 to 4 nm has increased the nanocomposite powder hardness by 11%. The microhardness and compression properties of an Al 2 O 3 /Al nanocomposite compact consolidated by hot pressing were measured. Comparison with modeled values and literature results indicates that the higher experimental yield strength obtained with the addition of n-Al 2 O 3 versus micron size Al 2 O 3 is due to in situ matrix strengthening.

A review of active distribution networks enabling technologies

Abstract: High levels of distributed generation have been installed in power systems and even a greater amount is expected to be deployed in the near future, with a large percentage likely to come from renewable energy sources. As such, Distribution System Operators (DNOs) will need to change their old “business as usual” passive approach, to one that adopts integration of control and communication technologies, together with emerging distribution network technologies, as a means of accommodating new generation in an optimal and economical manner. This paper presents a review of some of the impacts associated with the integration of distributed generation, together with some active distribution networks enabling technologies, intended to deal with the aforementioned problems. In particular, the present review focuses on technologies that are in advanced stages of Research and Development, or are even at the trial stage or are commercially available. However, further analyses are required in order to develop cheaper and more secure means to the increasing Distributed Generation connections.

Residual stress characterization in low transformation temperature 13%Cr-4%Ni stainless steel weld by neutron diffraction and the contour method

Abstract: This study presents the results of residual stress characterization by neutron diffraction and the contour method on 13%Cr–4%Ni welds made using 410NiMo weld filler metal. The transverse, longitudinal and normal components of stress were determined by neutron diffraction. The longitudinal stress distribution was also measured by the contour method. The last bead of the weld was found to be in a state of triaxial compression while a part of the heat-affected zone as well as a region beneath the weld were in a state of longitudinal tension. These results are explained with reference to the low martensitic transformation start temperature (Ms) of the alloy. The same measurements were made on an identical weld that had undergone a standardized post-weld heat treatment. The maximum tensile stress was reduced from 534 to 136 MPa, and the maximum compressive stress was reduced from 371 to 152 MPa.

Kinetics of the production of chain-end groups and methanol from the depolymerization of cellulose during the ageing of paper/oil systems. Part 2: Thermally-upgraded insulating papers

Abstract: In order to go further in demonstrating that methanol can be used as a universal cellulose degradation indicator in power transformers, the ageing study of standard wood kraft specimens in oil in the range of 60–130 °C (Gilbert et al. in Cellulose 16:327–338, 2009) has been extended to thermally-upgraded (TU) papers. The kinetic model that best tracks the ageing patterns was shown to be a function that can accelerate or decelerate the pseudo-zero kinetics by the adjustment of a free parameter. The results showed a non-negligible contribution of 1,4-β-glycosidic bond breaking in the crystalline regions suggesting that the degradation at this level is not necessary occurring through a quantum mode mechanism. The results also showed a significant error in the determination of the rate constants when obtained from isotherms of varying degree of depolymerization. In the case of TU papers, provided that there is a sufficient amount of stabilizers in the fibrous structure, not only could the self-catalyzing nature of the cellulose ageing process as well as the effect of an external supply of catalysts be lost but the chain-breaking could decrease to nearly zero for an undetermined period well before reaching the levelling-off degree of polymerization. The initial rate constants (k 1o) for the depolymerization and methanol formation of these papers were found to be very near those of standard cellulose (giving about the same activation energy), which indicates that they are obtained from the ageing patterns well before the retardant action has fully taken place. The life extension of TU papers is achieved by a reduction with time of the frequency at which the bonds are ruptured. Moreover, the production of methanol and chain-end groups showed about the same value for the frequency factor, which introduces the possibility that the rate of production of CH3OH from chopped chains is much higher than the rate of depolymerization, so that the latter becomes the rate determining step of the overall reaction. On the other hand, the apparent yield of CH3OH molecules per scission is seen to increase substantially with the amount of stabilizers (from ~0.4 to 0.8 and to 1.4 for a paper containing 0 to 1.15 and to 3.9% (w/w) N2) and to a lesser extent, with the moisture in the specimens. However, these variations could either be attributed to a modification of the CH3OH paper/oil partitioning by the stabilizers and moisture in fibrous structure. Finally, pre-aged systems (130 °C for 168 h) conditioned at 20 °C for variable lengths of time provided further evidence that O2 is not necessarily involved in CH3OH production.

Impact of startup scheme on Francis runner life expectancy

Abstract: Francis runners are subject to complex dynamic forces which might lead to eventual blade cracking and the need for corrective measure. Damage due to cracks in runner blades are usually not a safety issues but might generate unexpected down time and high repair cost. Avoiding the main damaging operating conditions is often the only option left to plant operators to maximize the life expectancy of their runner. The startup scheme is one of the available parameter which is controlled by the end user and could be used to minimize the damage induced to the runner. In this study, two startup schemes have been used to investigate life expectancy of Francis runner using in situ measurements. The results obtained show that the induced damage during the startup event could be significantly reduced with change to the startup scheme. In our opinion, an optimization of the startup scheme with regard to fatigue damage could extend significantly the life expectancy and the reliability of Francis runner.

On the application of VTOL UAVs to the inspection of power utility assets

Abstract: This paper presents a review of the state of the art and a discussion on vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) applied to the inspection of power utility assets and other similar civil applications. The first part of the paper presents the authors' view on specific benefits and operation constraints associated with the use of UAVs in power industry applications. The second part cites more than 70 recent publications related to this field of application. Among them, some present complete technologies while others deal with specific subsystems relevant to the application of such mobile platforms to power line inspection. The authors close with a discussion of key factors for successful application of VTOL UAVs to power industry infrastructure inspection.

An Online Control Algorithm for Application of a Hybrid ESS to a Wind–Diesel System

Abstract: Energy storage systems (ESSs) can be applied to mitigate some of the negative impacts associated with a variable power generation source such as wind energy. The control of ESS power must be accomplished over numerous time frames to meet system objectives and respect ESS capacity constraints. This paper proposes a two-level ESS control structure for use with a wind-diesel system, which is suitable for online implementation. The control is developed to coordinate power delivered from the two ESS levels in order to minimize diesel fuel consumption and limit up/down rates of the diesel plant. Different control modes are evaluated by simulation, and a subset of the results are validated using a hardware-in-the-loop representation. The controller that combines all three functionalities-minimizing dump load, limiting intrahour diesel ramp rates, and maximizing ESS utilization-demonstrates superior performance as measured by defined metrics and is proven to work online.

Nanodielectrics: A “universal” panacea for solving all electrical insulation problems?

Abstract: This text summarizes the keynote presentation that is based on the full-length paper of the same title. Dr. Frechette's oral presentation should not be seen as a summary of the “Brainstorm paper” but a glance at some major accomplishments, hinrances and still remaining questions relative to nanodielectrics. Are nanodielectrics a “universal” panacea∗? The answer to that question is no — but they've got a lot of potential!

PDC measurements to assess machine insulation

Abstract: DC testing is probably the most commonly used maintenance and diagnostic tests periodically conducted on machine stator insulation systems. With the commercial availability of more sophisticated equipment it is now possible to continuously monitor both charge and discharge current during a step voltage test, also known as polarization/depolarization current (PDC) test. This test is related to the dielectric response of the insulation system. This paper presents theoretical considerations on the dielectric response of the various types of machine winding insulation systems encountered in the field and the usefulness of using both the charge and discharge currents to assess the condition of the insulation system.

Rough Terrain Reconstruction for Rover Motion Planning

Abstract: A two-step approach is presented to generate a 3D navigable terrain model for robots operating in natural and uneven environment. First an unstructured surface is built from a 360 degrees field of view LIDAR scan. Second the reconstructed surface is analyzed and the navigable space is extracted to keep only the safe area as a compressed irregular triangular mesh. The resulting mesh is a compact terrain representation and allows point-robot assumption for further motion planning tasks. The proposed algorithm has been validated using a large database containing 688 LIDAR scans collected on an outdoor rough terrain. The mesh simplification error was evaluated using the approximation of Hausdorff distance. In average, for a compression level of 93.5%, the error was of the order of 0.5 cm. This terrain modeler was deployed on a rover controlled from the International Space Station (ISS) during the Avatar Explore Space Mission carried out by the Canadian Space Agency in 2009.

A Power Oscillation Damping Control Scheme Based on Bang-Bang Modulation of FACTS Signals

Abstract: In this paper, we develop a new damping control scheme for FACTS devices, using bang-bang modulation of FACTS signals. The scheme is used to attenuate quickly the system's most dominant mode which is identified using online Prony analysis. An analysis framework to evaluate the robustness of the control schemes to changes in operating conditions and to time-delay is also proposed. Simulation results on various test systems show that following large disturbances, the proposed control scheme is very effective to mitigate the power system critical modes of oscillation. Furthermore, the problem of control interactions is completely avoided with the proposed control scheme.

Restoration of the transepithelial potential within tissue-engineered human skin in vitro and during the wound healing process in vivo

Abstract: Normal human epidermis possesses a transepithelial potential (TEP) that varies in different parts of the body (10–60mV). The role of TEP in normal epidermis is not yet identified; but after skin injury, TEP disruption induces an endogenous direct current electric field (100–200mV/mm) directed toward the middle of the wound. This endogenous electric field could be implicated in the wound healing process by attracting cells, thus facilitating reepithelialization. However, little is known on the restoration of the TEP during human skin formation and wound healing. In this study, the variations in TEP and Na+/K+ ATPase pump expression during the formation of the epithelium were investigated in vitro using human tissue-engineered human skin (TES) reconstituted by tissue engineering and in vivo with a porcine wound healing model. Results showed that TEP undergoes ascending and decreasing phases during epithelium formation in TES as well as during wound repair within TES. Similar results were observed during in vivo reepithelialization of wounds. The ascending and decreasing TEP values were correlated with changes in the expression of Na+/K+ ATPase pump. The distribution of Na+/K+ ATPase pumps also varied according to epidermal differentiation. Taken together, these results suggest that the variations in the expression of Na+/K+ ATPase pump over time and across epidermis would be a determinant parameter of the TEP, dictating a cationic transport during the formation and restoration of the epidermis. Therefore, this study brings a new perspective to understand the formation and restoration of TEP during the cutaneous wound healing process. This might have important future medical applications regarding the treatment of chronic wound healing.

Nanodielectics. A "Universal" Panacea for Solving All Electrical Insualation Problems? [EXTENDED ABSTRACT]

Abstract: This is an extended abstract. The corresponding conference paper can be accessed at the following Web address: https://lra.le.ac.uk/handle/2381/10000

Experimental Investigation of the Hydraulic Erosion of Noncohesive Compacted Soils

Abstract: This paper presents the results of a laboratory investigation whose purpose was to evaluate the effects of compaction on the erodibility of cohesionless soils. By means of a recently developed flume experiment, sediment erosion rates and incipient motion, as a function of shear stress, average velocity, and dry density, have been determined for three compacted sand and gravel mixtures. A preliminary comparison of the incipient motion values shows that granular soils compacted at the Proctor optimum have a higher resistance to free surface flow erosion than those compacted at lower and higher densities. This leads one to infer that the Proctor optimum, generally used as a standard for construction, might also be an optimum for hydraulic resistance and stability. Additional comparison of the experimental data with two commonly used incipient motion criteria also suggests that Yang’s criterion is a better predictor of soil detachment than the Shields-Yalin criterion.

Ensemble decision trees for phasor measurement unit-based wide-area security assessment in the operations time frame

Abstract: This study proposes ensemble decision trees for phasor measurement units (PMUs)-based wide-area security assessment to provide early warnings of deteriorating system conditions. In the proposed technique, the wide-area response signals in real-time operation are captured after 1 and 2 s fault clearing time, from the respective monitoring buses where PMUs are placed. These wide-area post-disturbance records are processed in 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 called as wide-area severity indices (WASI). WASI are used as input features to train the random forests (RFs) to build effective predictor for early warnings in security assessment. The RF-based learning not only provides high performance accuracy but is also effective in valuing the importance of, and the interaction among, the various WASI input features, for developing the reliable predictor. The RF has been successfully tested for classifying both system-wise and area-wise NERC-compliant contingencies, using 55 196 cases (76 stable) from system operations studied on the Hydro Que bec network providing 99.9 reliability.