Time filter

Source Type

Pelissou S.,Hydro Quebecs research institute | Lessard G.,Hydro - Quebec
IEEE Transactions on Power Delivery | Year: 2011

This paper, the first of three parts, deals with the penetration depth and concentration of silicone fluid in cable insulation and its duration when injected in real-size, service-aged 28-kV extruded cables and subjected to various simulated service conditions in the laboratory. There were four aging conditions, namely, a cycling conductor temperature of 55 °C or 90 °C, in air or water, and with or without pressurized soak silicone, and always under service voltage. Samples were taken as a function of time and analyzed for silicone and water content in the insulation, and at the end for water treeing. The results indicate that the silicone content in the insulation changes circumferentially and can reach values between 1 and 4% after 96 thermal cycles, before stabilizing more or less up to 255 cycles. Furthermore, it was found that while water reacts with silicone, it contributes to the silicone retention in the insulation. Also, the study revealed that the number and size of water trees were not affected by the laboratory aging treatment and show no increase due to the presence of silicone. © 2011 IEEE.

Rafieian F.,Ecole de Technologie Superieure of Montreal | Hazel B.,Hydro Quebecs research institute | Liu Z.,Ecole de Technologie Superieure of Montreal
Procedia CIRP | Year: 2014

Robotic machining is emerging as a viable alternative for some conventional machining tasks. Nevertheless, a challenge to cutting performance remains: vibrational instability is reported to be more severe with robotic cutting due to robot compliance. In this paper, the regenerative vibrational instability of a robotic grinding operation is studied. The objective is to find the limit of stable operation when material removal is performed by a compliant robot. The traditional approach to regenerative chatter analysis is revisited for a robotic machining process developed at Hydro-Québec's research institute for tasks on hydropower equipment. Stability lobes are established with respect to system gain (ratio of cutting rigidity over robot stiffness) versus repeat frequency (ratio of spindle frequency over the robot's first natural frequency). Robotic machining is found to be far upper-right of the first stability lobe minimum, where system gain and repeat frequency are more than one order of magnitude larger than for conventional machining. The cyclic impacting dynamics of material removal in the operation under study is invoked to investigate instability in this region. A SDOF dynamic model for the robot is excited by an impact-cutting force and the stability of the simulated response is verified while increasing the cutting depth. The limit of stable impact cutting is thus determined for the process at typical rotational speeds, from which a stability boundary is plotted versus the repeat frequency. The boundary is found to be very close to the limit predicted using the traditional approach. It is concluded that the large gain is typical for robotic machining. The impacting dynamics of material removal due to robot compliance must be considered to understand such large gain values, never occurring in conventional machining. © 2014 Published by Elsevier B.V.

David E.,Ecole de Technologie Superieure of Montreal | Frechette M.,Hydro Quebecs research institute
IEEE Electrical Insulation Magazine | Year: 2013

The dielectric properties of a number of polymeric nanocomposites (PNC) have been investigated and reported, and there are very good reviews available, for example, see [1]-[3]. CIGRE Working group D1.24 has also performed several collaborative investigations on mostly epoxy- and polyethylene-based nanocomposites, which are reported in CIGRE publications [4], [5] as well as in archived papers [6], [7]. Dielectric nanocomposites investigated in the literature include various polyolefins such as polyethylene (PE; and PE blends) and polypropylene, ethylene vinyl acetate, polyamine, epoxy, and elastomers such as silicone rubber, containing various nanofillers such as metallic oxides, silica, alumina, titanium oxide, zinc oxide, and layered silicates (clays). Due to the very high specific surface area of nano-sized fillers, a few percent addition can significantly affect the dielectric properties of a polymeric material. The most common and practical processing methods suitable for thermoplastic nanocomposites are melt compounding, using a mixer, extruder, or both, and mixing in the liquid phase prior to polymerization for thermosetting resins, a process commonly called the in situ polymerization process [8]. Figure 1 gives examples of typical microstructures of polyolefin-based nanocomposites processed by melt compounding. The striking similarity of the microstrucmicro structure shown in Figures 1(b) and 1(c) should be noted as both were obtained in two different labs from the melt compounding of fumed silica and a thermoplastic resin using a twin screw extruder. Similar microstructures are also reported for isotactic polypropylene/SiO2 nanocomposites melt blended by extrusion [9]. © 2006 IEEE.

Vu V.H.,Ecole de Technologie Superieure of Montreal | Thomas M.,Ecole de Technologie Superieure of Montreal | Lakis A.A.,Ecole Polytechnique | Marcouiller L.,Hydro Quebecs research institute
Mechanical Systems and Signal Processing | Year: 2011

This paper presents improvements of a multivariable autoregressive (AR) model for applications in operational modal analysis considering simultaneously the temporal response data of multi-channel measurements. The parameters are estimated by using the least squares method via the implementation of the QR factorization. A new noise rate-based factor called the Noise rate Order Factor (NOF) is introduced for use in the effective selection of model order and noise rate estimation. For the selection of structural modes, an orderwise criterion called the Order Modal Assurance Criterion (OMAC) is used, based on the correlation of mode shapes computed from two successive orders. Specifically, the algorithm is updated with respect to model order from a small value to produce a cost-effective computation. Furthermore, the confidence intervals of each natural frequency, damping ratio and mode shapes are also computed and evaluated with respect to model order and noise rate. This method is thus very effective for identifying the modal parameters in case of ambient vibrations dealing with modern output-only modal analysis. Simulations and discussions on a steel plate structure are presented, and the experimental results show good agreement with the finite element analysis. © 2010 Elsevier Ltd.All rights reserved.

Jaoua A.,University of Montreal | L'Ecuyer P.,University of Montreal | Delorme L.,Hydro Quebecs research institute
Simulation | Year: 2013

The effect on multiskill call-center performance of pooling dependent call types is investigated. For this purpose, a copula-based modeling approach is used to provide multivariate models that take into account the call types' asymmetric dependence structures found in empirical data. Then, the realistic input models of the call-type-dependent arrival processes are used in a simulation study to explore the sensitivity of the pooling decision to this dependence. We find that the widely used assumption of independence, as well as the misspecification of the dependence structure, can lead to substantial misestimation of call-center performance. This demonstrates the importance of modeling call-type dependence in stochastic simulation studies of call centers. We also show, through case studies, that pooling two asymmetric left-tail-dependent call types is more likely to lead to low agents occupancy; whereas the presence of right-tail dependence structure increases the risk of service-level shortfall. This work provides new managerial insights to improve decision making in determining which call types to merge in the same pool in multiskill call centers. © 2013 The Society for Modeling and Simulation International.

Discover hidden collaborations