Time-stepping Finite Element Model Research Articles

Numerical modelling of transformers interturn faults and characterising the faulty transformer behaviour under various faults and operating conditions

Interturn short circuit faults are the leading cause of power transformer failures. If not quickly detected, these faults usually develop into more serious faults that would result in irreversible damage to the transformer, unexpected outages and the consequential costs. This contribution is aimed at obtaining a better understanding of physical behaviour of power transformers in the presence of interturn faults as well as extracting several features that would be useful to specify the faults. To this end, a circuit-coupled time-stepping finite-element model (FEM) of power transformer has been developed to characterise the transient behaviour of a real power transformer when the transformer is working under winding short circuit fault conditions. An experimental set-up consisting of the same transformer used with the FEM transformer simulation was used to validate the FEM of the faulty transformer. The results of the experiments demonstrate the remarkable ability of the model to reproduce the real behaviour of the transformer with interturn winding faults. The study characterises the faulty transformer behaviour under varying conditions of load, supplying voltage, location of the fault, and fault severity and size. Useful characteristic signatures associated with interturn faults extracted from the transformer behaviour under varying fault and transformer operating conditions are expected to yield insights into developing reliable and sensitive fault detection and localisation methods in power transformers.

A built-in force actuator for active control of lateral rotor vibration in cage induction electrical machines

In this paper means of active control of radial rotor vibrations in electrical machines are considered. We examine a built-in force actuator for active generation of force on the machine rotor. The operation of the actuator is based on electromechanical interaction between the rotor and the stator of the machine. The actuator is given a low-order linear state-space model, which is identified by using simulation data obtained from a detailed time-stepping finite element model of the machine. Simulation results obtained by using real machine data and finite element time-stepping method are presented.

Efficient magnetodynamic lamination model for two-dimensional field simulation of rotating electrical machines

This article presents a 2D–1D time-stepping finite-element model to evaluate the magnetodynamic rotational hysteresis effects in an electrical machine laminated cores. The 1D model is at first validated separately and then incorporated into the 2D model using an efficient iterative fixed-point procedure. A viscosity-based hysteresis model is applied in the lamination to account for the dynamic losses while the rotational field quantities are handled by a modified inverted vector hysteresis model. The 2D–1D model is evaluated by computing the core losses of an induction motor and experimental data of the motor are used for verification.

On-line broken-bar fault diagnosis system of induction motor

Induction motor faults including mechanical and electrical faults are reviewed. The fault diagnosis methods are summarized. To analyze the influence of stator current, torque, speed and rotor current on faulted bars, a time-stepping transient finite element (FE) model of induction motor with bars faulted is created in this paper. With wavelet package analysis method and FFT method, the simulation result of finite element is analyzed. Based on the simulation analysis, the on-line fault diagnosis system of induction motor with bars faulted is developed. With the speed of broken bars motor changed from 1 478 r/min to 1 445 r/min, the FFT power spectra and the wavelet package decoupling factors are given. The comparison result shows that the on-line diagnosis system can detect broken-bar fault efficiently.

Parameter Calculation of a Turbogenerator During an Open-Circuit Transient Excitation

A time-domain parameter calculation of a turbogenerator state-space model is presented. The finite-element (FE) method has been used to simulate a two-dimensional (2-D) nonlinear transient condition of the turbogenerator. An open-circuit transient excitation of the machine in closed-loop conditions (excitation system and unloaded synchronous generator) was reproduced to extract flux linkages, power losses, and eddy currents produced within the generator, which allowed the computation of the parameters of an electrical circuit. An electrical circuit structure with one d-axis damper winding is proposed. New parameter behavior profiles were found for the fictitious damper winding, and the saturation effects on the field winding reactance were determined. FE commercial software is employed during the research as a validation tool. It is found that the simulated time-domain response of the lumped model closely follows the time-stepping FE model. The research was carried out for a large turbine generator of 150 MVA, 13.8 kV, 50 Hz, and two poles.

Modeling bed-load transport of coarse sediments in the Great Bay Estuary, New Hampshire

Current, sea level and bed-load transport are investigated in the Lower Piscataqua River section of the Great Bay Estuary, New Hampshire, USA—a well-mixed and geometrically complex system with low freshwater input, having main channel tidal currents ranging between 0.5 and 2 m s −1. Current and sea level forced by the M 2M 4M 6 tides at the estuarine mouth are simulated by a vertically averaged, non-linear, time-stepping finite element model. The hydrodynamic model uses a fixed boundary computational domain and accounts for flooding–drying of tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this section of the system. The accuracy of hydrodynamic predictions in the study area is demonstrated by comparison with four tidal elevation stations and two cross-section averaged current measurements. Simulated current is then used to model bed-load transport in the vicinity of a rapidly growing shoal located in the main channel of the lower system. Consisting of coarse sand and gravel, the shoal must be dredged every five to eight years. Two approaches are taken—an Eulerian parametric method in which nodal bed-load flux vectors are averaged over the tidal cycle and a Lagrangian particle tracking approach in which a finite number of sediment particles are released and tracked. Both methods yield pathways and accumulations in agreement with the observed shoal formation and the long-term rate of sediment accumulation in the shoal area.

Analysis of Indirect Temperature-Rise Tests of Induction Machines Using Time-Stepping Finite Element Method

The ability to test the temperature rise of induction motors with indirect loading is very useful for the motor industry. In this paper different indirect loading schemes-including two-frequency methods, phantom loading methods, and inverter driven methods are analyzed. Their merits and drawbacks are highlighted. A universal method for analyzing all of these indirect temperature-rise methods is presented. The analysis is based on the time-stepping finite element model of skewed rotor bar induction machines, and the solution can include the effects of saturation, eddy-current, and the high-order harmonic fields directly. The computed losses can also include the stray losses due to the high-order harmonic fields. An 11 kW induction motor, when operating with normal full load and on phantom loading, has been used to verify the computed results.

Simulation of inverter-fed induction motor drives with pulse-width modulation by a time-stepping coupled finite element-flux linkage-based state space model

In this paper, a detailed description of the simulation of inverter-fed induction motors in adjustable speed drives by a time-stepping flux linkage-based coupled finite element/state-space model for the computation of the drive performance is presented and verified experimentally. The flux linkage-based state-space model is iteratively coupled to a 2D time-stepping finite element model. The iterative nature of the coupling between these two models facilitates rigorous modeling of the comprehensive impact of inherent space harmonics due to geometries and motor magnetics and time harmonics resulting from the electronic switching of inverters, as well as effects of the synergistic interaction between these time and space harmonics. The state-space model includes no frame of reference transformation in so far as the flux linkages, currents or voltages. This implies that the state-space model directly couples the motor to its power electronic controller in one formulation and the natural variables (voltages and currents) are directly involved in the formulation and computation. Finally, results of motor drive performance simulations and corresponding test results for a six-switch inverter with 180/spl deg/ e duty cycle for each switch and a six-switch inverter with pulse-width modulation are given with excellent test result correlations, respectively.

Time-stepping finite-element analysis of brushless doubly fed machine taking iron loss and saturation into account

The stator of a brushless doubly fed machine (BDFM) is furnished with two sets of three-phase windings. These windings always have different pole numbers and are generally supplied at different frequencies. Investigation of the field distribution in a BDPM indicates that no polar symmetry can be associated to it. In addition, the motion of the field is not a simple rotation, as in a induction motor. Therefore, it is not expected that the representation of saturation by means of traditional saturation factors will yield useful results. In this paper, the authors describe a time-stepping finite-element model for the BDFM which can readily represent the effect of saturation. In addition, it is shown that iron losses can be calculated as the time-stepping solution proceeds. The model is verified using measurements made on a test machine. The use of saturation factors in conjunction with an analytical model is also investigated.

Inclusion of interbar currents in a network-field coupled time-stepping finite-element model of skewed-rotor induction motors

In order to include the interbar currents of skewed-rotor inductor motors in finite-element analysis, a three-dimensional (3-D) model is usually necessary. In this paper a two-dimensional multislice time-stepping finite element method of skewed-rotor induction motors is presented to solve such complicated 3-D problems. It is shown that the network of the rotor cage is coupled to finite-element equations so that the interbar currents in the rotor can be taken into account. By arranging the unknowns and mesh-current equations ingeniously, the resultant coefficient matrix of the global system equations are made symmetrical. Compared with 3-D finite-element methods, the computation time for solving field equations with the proposed method is significantly shorter. The model can be used to estimate the high-order harmonic stray losses in induction motors. A comparison between computed and tested results is also given.