Calculation of machine winding electrical parameters at highfrequencies for switching transient studies

This paper describes a multiconductor transmission line approach for calculating the machine winding electrical parameters for switching transient studies. The technique is based upon the solution of the one dimension diffusion equation in the slot of electrical machines. The coil electrical parameters are calculated considering both the magnetic flux in the iron and in the air. Several practical formulations for calculating the winding electrical parameter are proposed which take into account the machine winding design characteristics. The computer models are validated by a comparison of measured and calculated results in two high voltage induction motors     

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Insulation failure significantly contributes to the unpredictable shutdown of power equipment. Compared to the partial discharge and high-frequency(HF) injection methods, the HF common-mode(CM) leakage current method offers a non-intrusive and highly sensitive alternative. However, the detection of HF CM currents is susceptible to interference from differential-mode(DM) currents, which exhibit high-amplitude and multifrequency components during normal operation. To address this challenge, this p...     

A generic transient PV system model for power quality studies

Currently, the deployment of PV technology in local distribution grids is usually done in an unplanned way without performing the required studies and this may induce power quality issues as penetration increases. The utilisation of accurate simulation models is therefore of great importance in an attempt to assess the real consequences of localised PV production. A generic PV system model for transient studies, the parameters of which can be tuned using transient data is proposed. The model is tuned and validated using transient data obtained from a detailed PV system circuit topology. The main novelty of this work lies in the fact that the proposed model can be tuned in order to represent accurately the dynamic behaviour of PV systems for both balanced and unbalanced conditions. Harmonics are also incorporated into the model to highlight its capability for use in complete power quality studies. The developed model is used along with the detailed PV system model to assess the voltage transient response of a distribution grid busbar. Finally, the transient behaviour of the distribution grid busbar having different grid impedance values is also evaluated utilising the proposed model. The expected and observed results are compared by means of the Theil Inequality coefficient depicting good agreement.     

A new energy recovery double winding cage-rotor induction machine

This paper proposes a new double winding induction machine and its speed control methods. The machine consists of two stator windings and one cage rotor. One stator acts as a motor and the other as a generator. By controlling the voltage supplied to the secondary or the generator winding, the rotor speed can be adjusted. The machine has a similar speed control characteristic to that of a slip-ring induction motor equipped with the rotor energy recovery scheme. The construction, principle, equivalent circuit, and speed control schemes of the new machine are presented. The performance characteristics of the machine are analyzed using the equivalent circuit and verified by experimental results.     

A mathematical model for refinery hydrogen network synthesis integrating multi-stage compressors

The synthesis of refinery hydrogen network (HN) is generally performed under the assumption that compressors are single-stage ones. This assumption might overestimate the compression power, leading to deviation from the optimum designs. To tackle this problem, we integrate multi-stage compressors into hydrogen networks synthesis in the present work. The number of compression stages inside each compressor is defined as a variable which is simultaneously optimized with the network configurations. Taking advantage of the discrete nature of the defined stage variable, we linearize the constraint of compression power without losing generality. The proposed mathematical model for HN synthesis is formulated as a mixed-integer nonlinear programming problem. Three instances are conducted and the solution results show that the proposed model could be solved to global optimality. The total annualized costs of globally optimal solutions are 1.4–5.1% lower than those of the base solutions.     

A 2-D model of the induction machine: an extension of the modified winding function approach

A new method to calculate the inductances of induction machines considering axial nonuniformity is proposed. The proposed method, an extension of the modified winding function approach, allows considering nonuniformity due to skew and static and dynamic air-gap eccentricity. Theoretical fundamentals and experimental results that validate the proposed method are presented.     

A stochastic fuel switching model for electricity prices

This paper develops and applies a novel electricity price model. We reproduce the merit order of a thermal-dominated electricity system by establishing a non-linear dependency of wholesale electricity prices on the prices of fuels (coal and natural gas) and of CO₂ emission allowances. The coefficients are estimated using a Markov Switching Regression.This approach might prove valuable for cross-hedging positions in the fuel, electricity and emission spot markets. It is also of use for studying the degree to which electricity prices in different countries reflect fuel and emission cost. Applying the model to the electricity markets of the UK and Germany, we find that British electricity prices are quite well-explained by short-run cost factors while the German ones are less well-explained.     

A transient ventilation demand model for air-conditioned offices

Ventilation to supply fresh air in an air-conditioned office consumes a considerable portion of energy in an air-conditioning system and affects the indoor-air quality (IAQ). The ventilation demand is primarily related to the occupant load. In this study, the ventilation demands due to occupant load variations were examined against certain IAQ objectives using the mass balance of carbon dioxide (CO₂) volume fractions in an air-conditioned office. In particular, this study proposed a transient ventilation demand model for occupant load, with the parameters determined from a year-round occupant load survey in Hong Kong. This model was applied to evaluate the performance of energy saving in different operating schedules of ventilation systems for typical office buildings in Hong Kong. The results showed that the energy consumption of a ventilation system would be correlated with the transient occupant load and its variations in the air-conditioned office. The ventilation system, with schedules taking account of the transient occupant loads, would offer a reduction in energy consumption up to 19% as compared with an operating schedule that assumed a steady occupant-load in the office during working hours. In both cases, the same IAQ objective was achieved.     

A modified lumped parameter model of distribution transformer winding

The modelling of the distribution transformer winding is the starting point and serves as important basis for the transformer characteristics analysis and the lightning pulse response prediction. A distributed parameters model can depict the winding characteristics accurately, but it requires complex calculations. Lumped parameter model requires less calculations, but its applicable frequency range is not wide. This paper studies the amplitude-frequency characteristics of the lightning wave, compares the transformer modelling methods and finally proposes a modified lumped parameter model, based on the above comparison. The proposed model minimizes the errors provoked by the lumped parameter approximation, and the hyperbolic functions of the distributed parameter model. By this modification it becomes possible to accurately describe the winding characteristics and rapidly obtain the node voltage response. The proposed model can provide theoretical and experimental support to lightning protection of the distribution transformer.     

Synchronous machine steady-state stability analysis using anartificial neural network

In the developed artificial neural network, those system variables which play an important role in steady-state stability, such as generator outputs and power system stabilizer parameters, are used as the inputs. The output of the neural net provides the information on steady-state stability. Once the connection weights of the neural network have been learned using a set of training data derived offline, the neural net can be applied to analyze the steady-state stability of the system in real-time situations where the operating conditions change with time. To demonstrate the effectiveness of the proposed neural net, steady-state stability analysis is performed on a synchronous generator connected to a large power system. It is found that the proposed neural net requires much less training time than the multilayer feedforward network with back-propagation-momentum learning algorithm. It is also concluded from test results that correct stability assessment can be achieved by the neural network     

Theoretical studies on transient pool boiling based on microlayer model

An analytical model for transient pool boiling heat transfer was developed in this study. The boiling curves of the transient boiling were obtained based on the microlayer model proposed by the authors and the mechanism of transition from the non-boiling regime to film boiling, i.e., direct transition was theoretically examined. Since the nucleate boiling heat flux is mainly due to the evaporation of the microlayer and its initial thickness decreases rapidly with increasing superheat, the duration of nucleate boiling is markedly decreased as the incipient boiling superheat is increased. It is found that the direct transition is closely connected to the rapid dryout of the microlayer which occupies almost the whole surface at high wall superheat.     

A doubly-fed induction machine differential drive model for automobiles

In this paper, an electrical drive model, implementing a doubly-fed differential drive (DFDD) is presented. Two doubly-fed induction machines, having the corresponding rotor phases connected, constitutes the differential wheel drive. Two inverters are supplying the machine stators with three-phase power of variable magnitude and frequency. The power required to supply the inverters may be delivered from a constant voltage DC source like a battery. Active power requirements for the machines and the inverters over the DFDD speed range may be obtained. Reactive power requirements for minimum copper loss may be derived as well. The DFDD may provide propulsion to electrical vehicles.     

A transient model for the energy analysis of indoor spaces

Using a finite-difference procedure, the dynamic energy response of indoor spaces under the influence of indoor energy pulses is analyzed. The method of analysis is simple and explicit and is based on the indoor surface thermal capacitance and heat-loss coefficient C_s and L_s respectively. It is demonstrated that these parameters characterize fully any specified indoor space, as far as its energy behaviour is concerned. Their values are calculated for an extended variety of indoor spaces, i.e. for various floor areas, floor dimensions ratios, indoor surface materials of envelope, partitions and furnishings, fenestration and indoor partitions areas. The range of validity of the present method of analysis is also defined and the corresponding deviations are quantified with reference to rigorous finite-difference solutions. The provided values of indoor space characteristics C_s and L_s may be used in a wide range of technological building applications, including comparisons and classifications of indoor spaces, design and selection of construction materials and furnishing as well as the investigation of effects from electric equipment, windows or doors opening, short-time ventilations, brief stay of visitors, etc.     

Advanced Backstepping controller for induction generator using multi-scalar machine model for wind power purposes

This paper presents a new non-linear control Algorithm based on the Backstepping approach for an isolated induction generator (IG) driven by a wind turbine. For this purpose and in order to reduce the complexity of the real induction machine mathematical model, the multi-scalar machine model is exploited. The machine delivers an active power to the load via a converter connected to a single capacitor on the dc-side. So, during the voltage build-up process, the necessary stator currents references to be injected by the converter are calculated from the desired active power to be sent to the load and the rotor flux magnitude. Simulation results show that the proposed control provides perfect tracking performances of the DC-bus voltage and the rotor flux magnitude to their reference trajectories.     

A hydrodynamic network model for interdigitated flow fields

The flow field is one of the main components of a fuel cell, which distributes the reactants to the active area of the cell and evacuates the products formed. Interdigitated flow field (IFF) is one among the different types of flow field designs that forces the reactants or products to flow through the electrode, thereby increasing the cell performance by decreasing concentration polarization loss, however, at the cost of higher-pressure drop. Prior understanding of the reactant and water vapour distribution in a flow field helps in obtaining the best flow field design. In the present paper, a model for the flow distribution and the pressure drop in an IFF has been developed using the analogy between fluid flow and electrical network in which the pressure is made analogous to the voltage and the flow rate to the current. The model, which ultimately reduces to the solution of a set of simultaneous algebraic equations, is capable of predicting the flow split among a set of inlet and outlet channels of an interdigitated flow field as well as the overall pressure drop for laminar, turbulent and two-phase flow conditions for arbitrary number of parallel channels. The results from the hydrodynamic network model have been validated against CFD simulations. This model can therefore be used for the optimization of interdigitated flow field design.     

A computer model for calculating steep-fronted surge distributionin machine windings

A computer model for predicting the distribution of steep-fronted surges in the line-end coils of machine windings is described. The model uses certain aspects of previous models combined to achieve simplification of solution while retaining accuracy. The solution technique is based on multiconductor transmission line theory and modal analysis. Parameter evaluation is based on the relationship between capacitance, inductance and wave velocity. The theory is extended to include a number of series-connected coils. Experimental and computational results are presented to illustrate the application and accuracy of the model     

A general model of synchronous machine for its steady-stateperformance analysis

A general model for analyzing a salient-pole machine as well as a nonsalient-pole machine under steady-state conditions is developed. The classical two-reaction theory method is replaced by the present method to analyze synchronous machines with salient-rotors. The method presented is applied to a 6.25 kVA test machine with a salient-rotor and is found to give accurate results     

A multi-segmented human bioheat model for transient and asymmetric radiative environments

This paper aims to improve the Salloum et al. multi-node multi-segmented model [M. Salloum, N. Ghaddar, K. Ghali, A new transient bio-heat model of the human body and its integration to clothing models, Int. J. Therm. Sci. 46 (4) (2007) 371–384] to accurately predict the circumferential skin temperature variation of nude and clothed human body segments when subject to complex transient and spatially non-uniform radiative environments. The passive bioheat model segments the body into the 15 cylindrical segments. Each body segment is divided into one core node, six angular skin nodes, one artery blood node, and one vein blood node. The model calculates the blood circulation using the Avolio model [A.P. Avolio, Multi-branched model of the human arterial system, Med. Biol. Eng. Comp. 18 (1980) 709–718] for arteries and arterioles up to 2 mm in diameter and the Olufsen et al., semi-analytical model [M.S. Olufsen, C.S. Peskin, W.Y. Kim, E.M. Pedersen, A. Nadim, J. Larsen, Numerical simulation and experimental validation of blood flow in arteries with structured tree outflow conditions, Ann. Biomed. Eng. 28 (11) (2000) 1281–1299] for small arteries and arterioles up to a minimum diameter of 0.3 mm; thus improving prediction of blood perfusion rates in the skin. Unsteady bioheat equations are simultaneously solved for the nodes of each body segment to predict the skin, tympanic, and core temperatures, sweat rates, and the dry and latent heat losses. The nude body thermal model is integrated to a clothing model that takes into consideration the moisture adsorption by the fibers to predict heat and mass diffusion through the clothing layers. The clothing layer is divided into six parts that are aligned to the skin sub-nodes for each clothed segment. The local and mean skin temperature can then be estimated in response to non-uniform environments.The nude body and the clothed model predictions were compared with published experimental data at a variety of ambient conditions, non-uniform conditions and activity levels. The current model agreed well with experimental data during transitions from hot to cold, dry to humid environments, and in asymmetric radiative environments. Both the nude and clothed human models have an accuracy of less than 6% for the whole-body heat gains or losses; the nude human model has an accuracy of ±0.35 °C for skin temperature values.