Marcelo Lynce Ribeiro Chaves

Three-phase transformer representation using FEMM, and a methodology for air gap calculation

This work deals with the representation of three-phase and three-limb transformers in two dimensions using FEMM (finite element methods on magnetics). The transformer magnetization curve is obtained using the magnetization characteristic for the silicon steel used when assembling the transformer core, associated to the air gaps inherent to the assembling process. A method for the calculation of the air gaps reluctance is presented and it is based on the transformer magnetic circuit and on the maximum value in each winding for the magnetization current waveform, such current is obtained through the no-load test. The magnetic flux distribution in the values and the effects of inherent air gaps in the magnetization current is analyzed. Through the use of post-processing procedures, the transformer leakage reactance is calculated and compared with values obtained through the experimental method. Therefore, one of the objectives, is to explain a method to insert some of the transformer assembling imperfections in the computer model.

Transformer Controlled Switching to Eliminate Inrush Current - Part II: Field Tests on a 100MVA Three-phase Transformer

Transformers are generally energized by random closing of the circuit breaker contacts, with the system voltage being applied on the transformer windings at random instants. This kind of switching normally introduces initial asymmetrical magnetic flux in the windings, driving the transformer into saturation. As a result, high transient magnetizing inrush currents are generated in the transformer, which may cause system disturbances. One of the solutions for mitigating these high inrush currents is to control the instants of the transformer energizing such that the magnetic flux produced in the windings corresponds, in magnitude and polarity, to the prospective core flux. This strategy is discussed in part I of this work. This part II presents the results of field test of energizing a 100 MVA, 230/138 kV, three-phase three-limbed iron core type transformer, carried out to validate the proposed strategy

Steam Turbines Under Abnormal Frequency Conditions in Distributed Generation Systems

Considerable efforts have been developed to encourage the installation of independent electricity producers in distribution systems. Obvious example of such efforts is demonstrated by the attempt to standardize their interconnection and protection requirements. However, this standardization can be difficult due to variations in the design of distribution circuits, the various types of generators coupled to the network and the particular requirements of each utility. However, a series of questions points to the development of further studies to ensure the quality of electric power, the system transient stabilty and lifetime of the blades of steam turbines (Moura et al.,2011).

The dynamic interaction of independent power producer synchronous machines connected to a distribution network in ATP-EMTP

The main task in this paper is to present a performance analysis of a distribution network in the presence of two synchronous generators in parallel, with its speed and voltage regulators modeled with TACS - Transient Analysis of Control Systems, for distributed generation studies. This type of configuration is common in systems where renewable fuels are used as sugar cane bagasse or straw. Must be highlighted that these generators are driven by steam turbines, and the whole system with regulators and the equivalent of the power authority system in the point of connection (CCP - Common Coupling Point) are modeled in the “ATP-EMTP - Alternative Transients Program”. Technical questions studied here refer to steady-state voltage profile, voltage stability, voltage dip due to a balanced three-phase fault, load rejection, distribution line outage and the behavior of machine regulators facing the aforementioned contingencies. Results show that, in some cases, the independent power producer (IPP) can be a risk to the physical integrity of the system and in other cases can be very beneficial to the distribution system in the point of connection.

Performance Analysis of Controlled Reclosing Procedure of Transmission Lines under Non-ideal Conditions

Transient overvoltage phenomenon related to transmission lines switching procedures is a quite well known subject, as well as the corresponding site effects that may affect the electrical system reliability as a whole. In the face of these occurrences, if mitigating measures are not taken, insulation faults in transmission lines and other components of the system can occur with relative frequency. Added to a set of classic procedures for the minimization of these phenomena, other possibilities, unconventional, have presented themselves as attractive options to the process in question. In this context, this paper explores the potentialities of a strategy established in the literature, which relies on so-called controlled switching technology. This procedure consists in the determination and use of optimum instants for the operational reestablishment of the line operation, after a possible disconnection and, from these, the switches are made without the undesirable overvoltages mentioned herein. Despite the fact that the fundamentals of this methodology are known, this investigation is imbued with the purpose of including non-ideal operational conditions that can, for real situations in the field, impact on the effectiveness of the method performance.

REGULADORES DE TENSÃO A NÚCLEO SATURADO: PARAMETRIZAÇÃO, MODELOS COMPUTACIONAIS E ESTUDOS DE DESEMPENHO

Despite recognition from a vast number of publications that contemplate performance studies of so called saturated core voltage regulators, the subject, when weighed against the benefits, such as new material based technologies and application perspectives, still presents various challenging topics. In fact, investigations concerning the physical principles governing its constructive design, the retrieval of representative electric and magnetic parameters, the development of computational models, enabling means for evaluating the effectiveness of the processes for restoring the busbar voltage are still deserving of research, development and modelling. Given this setting, the present paper cogitates aspects that guide the physical design concepts and parameterization of these devices, strategies aimed at the computational modelling and evaluation of these devices performance at regulating voltages and other correlated phenomena. Theoretical results are compared to corresponding experimental performances intent on defining the established models’ degree of adhesion. Keywords: Saturated Core Reactors, Design and Modeling, ATP Simulator, FEMM Simulator, Voltage Regulators.

Lightning overvoltage investigation due to a backflashover event in transmission lines: A realist modeling proposal

This paper presents a study about the lightning performance of transmission lines using advanced electromagnetic models to perform a realistic representation of the first stroke current. Based on the measurement data obtained at the Morro do Cachimbo/MG Station, it was possible to synthesize first stroke current waveforms with single- an double-peak in a realistic way. In addition, the investigation involves an analysis with a model implemented in ATP-Models to reproduce the first stroke current recommended by CIGRÉ methodology. The breakdown process was represented through a Leader Progression Model able to represent accurately the physical process established along the perimeter of the insulator strings, during a backflashover event. The results allowed an investigation of the waveforms and amplitudes of the resulting overvoltages across the insulators. The computational modeling developed permits to identify the amplitude of the overvoltage that produces the backflashover and the instant of time that the breakdown occurs.

Grid integration of renewable sources in the distribution Network: An analysis through ATPEMTP

The main objective of this work is to present the analysis of the behavior of synchronous generators of an electrical energy independent power producer, with their respective automatic voltage regulators (AVRs) and speed governors, in parallel with a power authority distribution system, for the distributed generation studies. It is highlighted that this generator is driven by a steam turbine with regulators and governors modeled in “ATP-Alternative Transients Program”, through the use of TACS subroutines. Among the analysis to be made are, the monitoring of voltage levels at the Common Coupling Point (CCP), before and after the Independent Producer (IP) entry point, as well as the analysis of the opening of the interconnection breaker and balanced three-phase fault. Moreover, the analysis of responses for the synchronous machines controls, voltage regulator and speed governor, are also the subject of analysis in this paper. The impacts of such generators in distribution networks are determined and compared through the use of a model of a distribution network, also modeled in ATP. This work presents, clearly and in a well defined manner, the main modifications in the power electrical system, more specifically in distribution networks, due to the presence of an independent power producer with two synchronous machines.

A comparative investigation on three-phase transformers modeling with and without magnetic coupling between phases

Three-phase transformer models in EMTP-like programs have been usually carry out through an association of three single-phase transformers, without taking into consideration the magnetic coupling between phases produced by the yokes of the transformer ferromagnetic core. It has been found, however, that this magnetic coupling is essential when power system unbalanced phenomena are to be studied. In this paper it is shown the simulation results of a comparative investigation between two three-phase transformer models: one represented by a bank of three single-phase transformers (no magnetic coupling) and one that considers the magnetic coupling between phases. Various situations of system imbalance are simulated and discussed.