J.L. Guardado

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.

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.

Analytical method for optimization of maintenance policy based on available system failure data

An analytical optimization method for preventive maintenance (PM) policy with minimal repair at failure, periodic maintenance, and replacement is proposed for systems with historical failure time data influenced by a current PM policy. The method includes a new imperfect PM model based on Weibull distribution and incorporates the current maintenance interval T0 and the optimal maintenance interval T to be found. The Weibull parameters are analytically estimated using maximum likelihood estimation. Based on this model, the optimal number of PM and the optimal maintenance interval for minimizing the expected cost over an infinite time horizon are also analytically determined. A number of examples are presented involving different failure time data and current maintenance intervals to analyze how the proposed analytical optimization method for periodic PM policy performances in response to changes in the distribution of the failure data and the current maintenance interval.

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.

Distributed Parameters Model for High-impedance Fault Detection and Localization in Transmission Lines

Abstract A high-impedance fault is generated when an overhead power line physically breaks and falls to the ground. Such faults are difficult to detect and locate in electric power systems because of the small currents and voltage drops involved, which cannot be detected by conventional protection. Furthermore, arcing accompanies high-impedance faults, resulting in fire hazard, damage to electrical equipment, and risk to human life. This article presents an analytical description of the interaction between the electric arc associated with high-impedance faults and a transmission line. A joint analytical solution to the wave equation for a transmission line and a non-linear equation of the arc model is found for the case of an arbitrary reflection coefficient at the substation end, and a methodology for high-impedance fault detection and localization is proposed. The developed model is validated by means of a comparison with measurements. The comparison demonstrates the accuracy and effectiveness of the proposed model.

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 Control System for Static VAr Compensator Based on a Digitally Controlled Oscillator

Abstract This article deals with the design, construction, and testing of a new control system for a static VAr compensator. The new control system is based on monitoring reactive power, which is used as the only feedback variable for a digitally controlled oscillator. In addition to synchronizing the static VAr compensator with the AC system, the digitally controlled oscillator also schedules the firing of converter valves in order to achieve the reactive power compensation level required in the AC connection bus. The control system design was initially developed in MATLAB® and Simulink® (The MathWorks, Natick, Massachusetts, USA), and then a ±1-KVAr static VAr compensator experimental prototype was built. The static VAr compensator control system was implemented in a PIC16F877 microcontroller (Microchip Technology Inc., Chandler, Arizona, USA). Computer simulations and experimental results for the static VAr compensator and its control system are presented in the article. Finally, the performance of the proposed static VAr compensator control system was compared with a phase-locked loop control system for a static VAr compensator, and the relevant results are presented.