E. Melgoza

An improved arc model before current zero based on the combined Mayr and Cassie arc models

A computer model that describes the dynamic arc behavior in the high- and low-current regions before current zero is proposed. The model divides the current and voltage waveform in two regions. A differential equation for both regions which unifies current and voltage time derivatives is obtained by means of a generalized function method. The computer waveforms reproduced with the model show good agreement with measured results published in in the low and high current regions, but further comparison with other test measurements are required to know if the model has any feature of predictability.

Comparison of table models of electromagnetic actuators

A number of possibilities for constructing table-based lumped-parameter models of linear or rotary actuators are compared. Two of them have not been published previously. The accuracy of the models is evaluated by comparing simulated results against experimental measurements taken from a prototype actuator. The computational cost of the models is also discussed.

Coupling Circuit Systems and Finite Element Models: A 2-D Time-Harmonic Modified Nodal Analysis Framework

A new, systematic way of coupling low-frequency finite-element (FE) models with circuit systems is proposed using a modified nodal analysis framework. Solid and filamentary conductors can be equally treated as magnetic vector potential-controlled voltage sources. Their matrix contributions to the coupled system are basically the same, leading to a natural way of adding conductors to arbitrary circuit topologies. Algebraic equations of the same type describe the coupling between FE and circuit models, for both massive and filamentary conductors. Any class of independent and dependent source can be considered as well as resistances, inductances, capacitances, transformers, auto-transformers and magnetically-coupled branches. The resulting matrix for the coupled problem is symmetric if the circuit configuration does not contain voltage- or current-controlled sources. The methodology is developed for the general nonlinear time-harmonic problem, but it can be extended to the transient case. An induction motor test case is employed to show the power of the new coupling approach. Comparison of the results against a well-known, validated commercial software (Flux2D) shows that the code developed in this work performs efficiently.

Systematic Coupling of Multiple Magnetic Field Systems and Circuits Using Finite Element and Modified Nodal Analyses

Existing circuit-field coupling schemes can deal with a single magnetic field model connected to an external circuit. However, modern electrical systems are a complex interconnection of multiple magnetic devices, which opens up the question of how to consider multiple interacting field models. In this paper, we propose a scheme based on the finite element and modified nodal analyses, to solve the problem of coupling multiple magnetic field systems with circuit networks. The proposed methodology is systematic since each element within the electrically connected problem has a building block, which is easily inserted into the global system of equations. This applies to any magnetic field system, where massive and filamentary conductors are equally accommodated. Hence, each electrical network component can be modeled with any desired level of detail: as a magnetic system (distributed parameter model) or as a circuit (lumped parameter model). To show the flexibility and power of the proposed methodology, the finite-element models of a three-phase induction motor and a transformer are electrically interconnected through circuits that represent an infinite bus bar and a short transmission line.

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.

Multi-Slice Modeling in Circuit-Field Coupled Systems Using Finite-Element and Modified Nodal Analyses

We propose a systematic method for interfacing different 2-D low-frequency electromagnetic field slices and nonidentical multi-port circuit networks using finite-element (FE) and modified nodal analyses. Each independent field slice has its own length, geometry, materials, boundary conditions, and number of filamentary and massive conductors. Similarly, each multi-port circuit network can have different circuit elements, topology, and number of ports. As a result, field slices are not required to be successively connected, since multi-port circuit networks can exist between them. Thus, solutions for virtually any possible configuration of 2-D circuit-field coupled systems are possible. The number of slices and multi-port networks does not affect the general form of the final system of equations, which is symmetric for most practical cases. Although we developed the methodology for 2-D time-harmonic magnetic problems, it can be readily extended to the transient case. We analyzed an induction motor to test the proposed multi-slice FE approach and validated the results using the total short-circuit leakage reactance and commercial software (Flux2D).

Distance protection coordination using search methods

In this paper, a methodology for calculating the setting impedance of zones 2 and 3 of distance relays is presented, The aim is to reduce protection coordination problems during fault occurrence and changes in the network configuration. The proposed method is based on the impedance seen by the distance relay when faults are simulated on adjacent nodes. The coordination and relay setting is obtained by means of computational algorithms developed to analyze the network topology, determine the pair of primary-backup relays and short circuit studies considering several types of faults in the power system. This process is carried out in an object oriented environment which allows a flexible approach to the user of the software. In the development of this tool search methods based on graph theory were used. The method was applied to an IEEE 14 nodes test system with satisfactory results.

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.

A surface impedance method for moving conductors

Some techniques for modeling thin skin depth eddy currents induced by the movement of a conductor through a magnetic field are described. The nonconducting regions are modeled using conventional volume finite elements in terms of the magnetic scalar potential /spl psi/. The magnetic fields in the thin skin are determined approximately using either analytic or numerical solutions to 1D equations for fields in the moving skin.