ATCO (Canada)

Our modelling of brain mechanics is based on observations of Budday and colleagues [6], who analyzed the elastic properties of human brain tissue samples under multiple loading modes. Using these data, Budday et al. determined a realistic constitutive model for brain tissue mechanics. In these studies, they found that compression and shear responses were best modelled by a non-linear one-term Ogden elasticity model, although other elasticity models are possible as well. Here we analyze the role of the elasticity model of brain tissue on the invasion speed of glioma and the resulting tissue deformation (mass effect). We present a one dimensional continuum model that couples cell dynamics to tissue mechanics. Since the mechanics of glioma-compromised brain tissue is not clear, for comprehensive studies, we incorporate both elastic and viscoelastic versions of two brain tissue elasticity models - the commonly employed linear model and the experimentally determined one-term Ogden model. For each elasticity model we identify travelling wave solutions in one dimension and calculate the corresponding invasion speeds. We find that the invasion speed is, in fact, independent of the chosen elasticity model. However, the deformations of the brain tissue, and resulting stress, between the linear and one-term Ogden models are drastically different: the Ogden model shows two orders of magnitude less deformation and three orders of magnitude less stress as compared to the linear model. Such a discrepancy might be relevant when looking at glioma-induced health complications. Statement of significanceCancers arising from glial cells, known as gliomas, form in the spine and the brain. The spread of glioma is not fully understood, although recent studies have highlighted the role of tissue mechanics as a main factor in the invasion process. We present a one dimensional continuum model framework of glioma invasion that incorporates proliferation and invasion of glioma cells, as well as mass effects by coupling cell dynamics to tissue mechanics. We explore both elastic and viscoelastic versions of two brain tissue elasticity models - the commonly employed linear model and the experimentally determined one-term Ogden model. This is the first time the one-term Ogden model has been incorporated into a model of glioma invasion. We show that although the choice of elasticity model does not affect the invasion speed, the deformation and stress generated in the tissue are significantly different with the Ogden model producing three orders of magnitude less deformation and stress as compared to the linear model. Such a discrepancy might be relevant when looking at glioma-induced health complications.

Power system reliability is largely affected by the conditions of power system equipment. Therefore, to accurately determine power system reliability and proper asset management strategies, it is important to understand the condition degradation processes of different equipment. When there is sufficient historical condition data, equipment degradation can be modeled based on such data; however, utility companies often face the situation where historical condition data is not properly recorded, tracked or stored for all the large amount of equipment utility companies have to manage. To solve this dilemma, this paper explored a solution from an unconventional angle - it investigated models for simulating the non-destructive condition degradation of power system equipment. Initial effort and results are presented in this paper along with future research suggestions identified.

Flexible ac transmission system (FACTS) devices are often a recommended option for improving power quality. The most common shunt-connected FACTS device, namely the STATCOM, has become a viable option for distribution systems and has been employed for mitigating instances of voltage fluctuation, voltage unbalance, and in some cases harmonic distortion. As a distribution application, it has been termed D-STATCOM. D-STATCOMs also aid reducing the amount of reactive power drawn from the distribution system, reducing overall ampacity and aiding voltage management. However, it is well known that the degree of compensation provided by a D-STATCOM is a direct relationship with the system X/R ratio. For typical distribution systems, this results in large reactive power rating to perform appropriately. Unless an optimized reactive power scheme is developed, this will translate into large equipment rating near its installation site. This paper proposes a distributed reactive power management scheme, where reactive power is provided by one or more D-STATCOMs. The scheme is intended to boost low steady-state voltages and its output prescribes the instantaneous reactive power output of each participating D-STATCOM. For system boundary conditions, it also dictates the device rating. The proposed method is supported by an analytical development that estimates the amount of outputted reactive power to manage the voltage with a planning-specified voltage rise. Case studies representing real rural distribution systems applications are presented to demonstrate the proposed scheme.

There have been strong drivers toward lessening diesel dependency in remote communities. These off-grid communities can be difficult to access, and often face challenges with diesel supply. More importantly, governments are striving to improve the environmental outlook in these areas. Tying this need with associated high operational costs and fuel handling challenges, alternative sources of energy and energy storage have emerged as a viable option to reduce diesel consumption. This paper presents the experience of a Canadian electric utility in planning the application of utility scale photovoltaic generation and Battery Energy Storage Systems to supplement existing diesel generators in a remote isolated community in Alberta. Economic drivers and opportunities to partner with first nations have sparked stakeholder attention and positioned the project as a national interest. Technical and economic studies were conducted to address all aspects of the project. These include forecasting load, sizing and siting each alternative generation option, customizing dispatch strategies, and determining required spinning reserve from diesel generators through time-domain studies. This paper covers the size and location optimization of the PV and BESS assets and dispatch strategies.

This paper investigates the overvoltage problem caused by micro-generators (MGs) in secondary distribution feeders. The allowable MG active power injection into a particular feeder essentially depends on the system R/X ratio, supply impedance (system fault level) and feeder topology. Different from transmission systems, distribution systems exhibit a high R/X ratio, involving large amount of reactive power for voltage regulation which cannot be entirely provided by MGs alone. Hence, a limit exists on the allowable MG power injection within acceptable voltage rise tolerances. This paper presents analytical and case studies, clarifying the relation between MG power, feeder characteristics (R/X ratio and fault level) and voltage rise. It also provides some useful charts and equations to estimate voltage rise, maximum allowable MG power and required reactive power for typical R/X ratios and fault levels. The application of switchable shunt inductors as means of voltage rise mitigation in secondary distribution systems with high R/X ratios is also demonstrated in this paper.

Stray voltages have always been a concern to utility companies and customers. But methods to troubleshoot and monitor nonroutine stray voltage problems are very limited. This paper presents a passive, measurement-based method to identify the contributors to the common cause of stray voltages, the neutral-to-earth voltage (NEV) rise at the service entrance point. The paper shows that the NEV can be decoupled into two components: those related to the customer under investigation and those outside the customer facility. A method to quantify the relative contributions of the two components is proposed. A new concept called current return ratio is introduced to facilitate the decoupling and to quantify the grounding conditions of the system. This paper presents the background, circuit model, concept, and theory of the proposed method.

Electrical Submersible Pumps (ESPs) are commonly used in deep wells in oil and gas industry. In order to monitor ESP systems operating conditions, downhole monitoring tools are used to transmit data representing physical conditions of downhole such as temperature, pressure, and vibration to the surface. The most common downhole communication method implemented in the field is to use a DC signal over three phases of the main power cable and uses the ground as a return path. However, this method cannot operate in the event of a single-phase-to-ground fault, because the signal path would be shorted although the electrical submersible pump is still in operation due to the ungrounding practice in downhole ESP systems. Experience has also shown that this existing method is prone to failure in presence of unbalance conditions in the system. In this paper, a new phase-to-phase communication scheme for the downhole monitoring tool design is proposed where intentional disturbances in the power supply to the motor are used as means of binary communication. The proposed scheme is immune to single-phase-to-ground faults and unbalance conditions. Theoretical formulas defining this method are developed and the performance of the method is evaluated using simulation through case and sensitivity studies.

This paper proposes the use of the SVMs classification technique for power transformer protection, in order to enhance the detection of minor internal turn-to-turn faults. The proposed scheme has been also tested through external faulted cases as well as energizing inrush phenomenon. In addition, it has been compared with a conventional differential algorithm. The results have shown that the proposed intelligent technique provides fast, sensitive and reliable detection of minor internal turn-to-turn faults in power transformers. The dynamic simulations of a test benchmark have been conducted using the PSCAD/EMTDC software.

Slot discharge and VS are two stator winding deterioration mechanisms acting on stator winding insulation. Slot discharge can have at least three different causes only one of which is caused by bars vibrating in the slot. Slot discharge will be significant only in bars that are operating at or near rated voltage. Vibration sparking will only occur when two conditions are met simultaneously: a) the slot conductive coating is too conductive, and b) the bars are vibrating in the slot. This can occur throughout the stator.The manifestations of the two mechanisms can be very similar. The major difference between slot discharge caused by loose coils and VS is that VS can occur on bars located anywhere within the winding. Vibration sparking is generally the more aggressive of the two mechanisms. Because the root cause and corrective actions are quite different, it is important to distinguish between the two mechanisms. The presence of VS or slot discharge in a stator winding can have significant influence on the projected life of a stator winding. Thus it is important to detect and correctly diagnose either problem in its early stages. If the amount of activity is significant and advanced, repair may be difficult or impossible, particularly in the case of VS.