Vicente Venegas

A machine winding model for switching transient studies using network synthesis

This paper describes a computer model for calculating the surge propagation in the winding of electrical machines. The model considers the winding as a combination of a multiconductor transmission line and a network of lumped parameters. The frequency dependence of the winding electrical parameters is calculated and incorporated into the analysis by means of Foster and Cauer circuits. The multiconductor transmission line provides the surge propagation characteristics for the winding model and its parameters are calculated from machine design characteristics. Finally, this hybrid model is validated by a comparison of calculated and measured results inside a high-voltage machine winding.

A three-phase model for surge distribution studies in electrical machines

This paper describes a computer model for surge distribution studies in the windings of electrical machines. The computer model takes the coil as the basis for the analysis and uses multiconductor transmission line theory to obtain the transference matrix for the winding. Several practical formulations based on machine design characteristics are used for calculating electrical parameters. Flux penetration into the iron core and mutual coupling between coils in different phase windings are incorporated into the analysis. The model was validated by a comparison of predicted and calculated results in a high voltage motor.

Transient overvoltages in electrical motors during sequential pole closure

This paper addresses the problem of transient overvoltages in electrical motors during sequential pole closure in industrial installations. A computer model that includes the circuit breaker, high-voltage cable and electrical motor is proposed. Multiconductor transmission line theory and modal analysis are applied to the components and the piecewise Fourier transform is used to simulate sequential pole closure. The mechanism of sequential pole closure is analyzed including parallel capacitors and series inductors. Critical times for switching transients are calculated. Finally, the effect of several system and machine parameters on transient overvoltages is investigated.

Strong Coupling of Electromagnetic Transients and Finite Element Magnetic Field Solvers

Magnetic devices such as transformers and rotating electrical machines are key components of modern power systems and the simulation of transient events involving them is fundamental. In this paper, a method for strongly coupling a power systems transients program with a finite element field solver is proposed, which eliminates the time step delay in the solution of the two separate domains, and therefore avoids the instability which otherwise could arise. The field model provides an accurate computation of the magnetic field distribution in the device, taking into account the ferromagnetic core nonlinearity and spatial effects, while the electrical network is represented by a circuit model. The transients program used for the coupling is the Alternative Transients Program (ATP), and the field solver is FLD. The simulation scheme and its implementation have been verified by comparison with a directly coupled circuit-field solver.

Computation of Differential Inductance and Flux Linkage Positional Derivative by a Sensitivity Approach

The differential inductance and flux linkage positional derivative are important parameters in the analysis and simulation of electrical machines where saturation is nonnegligible. A new method for the computation of these quantities for devices with an arbitrary number of windings is presented. The method is based on the determination of the sensitivity of the magnetic vector potential to variations in the input current vector or the rotor position, in the context of finite-element formulations. The implementation of the proposed method for plane Cartesian and axisymmetric cases is considered in detail. The method and its implementation are verified by comparisons against known inductance formulas or results from other computational methods. In the case of the differential inductance, the proposed scheme is an alternative to energy perturbation methods, while the determination of the flux linkage positional derivative is made in one step for the first time.

Strong coupling of circuit and field solvers for simulation of rotating electrical machines

Coupled circuit-field solutions provide a powerful tool to simulate the detailed behavior of electrical machines and other magnetic devices operating as part of a larger system. The coupling of both domains can be made inside a single analysis tool, or it may be attempted by combining two separate-domain programs, thus taking advantage of the individual strengths of existing numerical codes. In this paper, a scheme to implement the latter type of coupling is presented, which extends a previously proposed static method to consider movement of the rotor or some other moving part. The system-level simulator is the Alternative Transients Program (ATP), and the magnetic field solver is FLD. The proposed scheme provides a strong coupling between circuit and field variables and therefore is free from the stability problems which often arise in weak coupling schemes. The method is applied to a test rig resembling a switched reluctance motor, and the results are compared with published measurements.

A computer model for surge distribution studies in transformer windings

In this work, a computer model for calculating surge distribution in power transformer windings is presented. The model is based on multiconductor transmission line theory, considering each disk coil as the basic element for the analysis. The electric parameters R, L, C and G are calculated by using conventional formulations. The electrical parameters are used for calculating modal parameters in order to represent the winding as a two port network. The transformer model is validated by means of a comparison between measured and calculated transient voltages in a phase winding with 34 coil disks, in a scaled down prototype of a power transformer.

A Perturbative Method for Calculating the Impedance of Coils on Laminated Ferromagnetic Cores

A new set of formulas for calculating the self and mutual impedances of coils on straight and closed laminated ferromagnetic cores of circular cross-section has been derived. The obtained formulas generalize the well-known formulas for impedances of coils on homogeneous ferromagnetic cores, for the case of laminated cores, and improve the previously known formulas for laminated cores. The obtained formulas are fully consistent with Maxwells equations and, therefore, offer an excellent accuracy. The perturbation theory and the average field technique are used to solve Maxwells equations inside and outside the core. The solution inside the core can also be used in the analysis of thermal effects occurring inside the laminated core.

A method of obtaining of electric arc model parameters for SF 6 power circuit breakers

A new method of calculating parameters of electric arc model of SF6 power circuit breaker is proposed. The methodology consists in the optimization of a theoretical function with respect to a group of parameters of model in order to achieve a better approximation to a set of experimental data. The theoretical function is an asymptotic solution for the voltage that is obtained for a selected period of time. The developed method is applied to obtain the parameters of an arc model previously published in the literature. By means of a variation of the cooling power P0+P1iu, a new electric arc model is obtained including the additional parameters of model. The new model has a very compact form and results in a better correlation between the theoretical voltage curves and the experimental oscillograms.

A frequency domain transformer model for simulating fast transient overvoltages

In this work a computer model for calculating surge distribution in transformer windings is presented. The transformer model is developed using transmission line theory. The capacitance, inductance, resistance and conductance are calculated with simple formulations. The electrical parameters are used for calculating modal parameters in order to represent the winding as a two port network. The model is validated by means of a comparison between measured and calculated voltages in a power transformer disk with 16 turns.