Braz de Jesus Cardoso Filho

Simulation and analysis of induction machines with rotor asymmetries

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such effort is the modeling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. In this paper, a new and simpler approach for the modeling of induction machines with rotor asymmetries is employed in the simulation and analysis of an induction motor with rotor asymmetries. Simulation and finite element analysis results are presented to support the proposed approach.

Determination of the magnetic losses in induction motors based on the generalized Epstein test

The results obtained from the standard method for the characterization of magnetic materials - the Epstein test - lead to significant errors in the estimation of magnetic losses in induction motors. Among the induction motor characteristics not accounted for in the Epstein test method, one can point out: winding distribution, cutting stresses, anisotropy, PWM supply and rotor losses (surface losses and interbar current losses). The generalized Epstein test method - GET - is introduced as an alternative to improve the estimation of magnetic losses in induction motors from tests performed on core material samples similar to the ones used in the standard Epstein test. In this paper, the GET is discussed and applied in the estimation of the magnetic losses in induction motors build from different core materials. Associated methods employed in the determination of the proper excitation harmonics and computation of rotor magnetic losses are also discussed. Experimental results are included to illustrate the proposed method.

A new method to simulate induction machines with rotor asymmetries

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such effort is the modelling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. This paper introduces a new and simpler approach for the modelling and computer simulation of induction machines with rotor asymmetries. This approach is based on the well known dq transient model of the symmetrical machine, with rotor asymmetries introduced through a linear transformation of the extended rotor current vector. Simulation and practical results previously presented in the literature are reproduced to support the proposed approach.

Minimum reactive power filter design for high power converters

This work proposes and evaluates an optimized filter design for high power converter with sinusoidal voltage and current. The inherent low switching frequency of this class of converters complicates the filter design and generally results in large filter components. The proposed design culminates in minimum filter reactive power, size and cost. Simulation and experimental results support those ideas.

Increasing long belt-conveyors availability by using fault-resilient medium voltage AC drives

Belt conveyors constitute an efficient and economical way for minerals and heavy load transportation from mines to their destination, they serve vital process units whose success depends on continuous operation. To meet important operational requirements, modern high capacity conveyor systems are equipped with medium voltage variable-speed induction motor drives. The reliability and service continuity of such drives play a critical role for the entire conveyors availability. This work proposes a way to significantly improve the availability of the conveyor systems by using fault-resilient medium voltage AC drives. Based on recent studies and authors experience, it is shown in this paper how the drive conveyor downtime can be dramatically reduced after an internal short-circuit, keeping the overall cost-to-repair to a minimum and avoiding financial losses that can reach several million dollars.

Application of solid state transformers in utility scale solar power plants

With the increasing participation of PV sources in the international energy market, more efficient inverter topologies and modules connections are desired. Large-scale PV plants (solar farms) use generally the central inverter topology, in which the PV modules are distributed into few maximum power point trackers. Although this topology has typically high efficiency, it has low MPP tracking performance. This paper proposes a modular converter based on solid state transformers (SST), in which high frequency transformers are used replacing the bulky medium-voltage line-frequency ones. In this technology, the converter output is provided by the series connection of the DC-DC-AC converter stages, supplied by independent PV module arrays. Among its many advantages, one can point out their reduced size and weight, improved reliability and easier maintenance of the system. This paper presents the proposed SST based converter topology for PV power plants and addresses some of its control issues.

Load Torque Signature Analysis: An alternative to MCSA to detect faults in motor driven loads

In this paper, an alternative to the MCSA (Motor Current Signature Analysis) method to detect faults in motor driven loads is presented. The proposed method named Load Torque Signature Analysis - LTSA - processes an estimative of the load torque to obtain a signature of the fault on the load. A comparison of the LTSA and MCSA method is done under the viewpoint of frequency bandwidth, sensitivity and implementation drawbacks. The influence of electrical and mechanical parameters on LTSA performance is investigated. Mathematical relationships among these parameters which allow establishing the nature of the frequency response are obtained. It is shown that, LTSA can be an interesting alternative to be applied in several situations where MCSA performance is poor. Simulation and Experimental results validating the studies are presented.

Analysis of the operation of a D-STATCOM in unbalanced distribution systems under voltage disturbances

In this paper, a study on the operation of a static synchronous compensator for distribution systems, D-STATCOM, in relation to its performance in the presence of events that can affect systems power quality, is presented. Performance under short-circuit and load variation is assessed. The IEEE 13 node test feeder, which is a highly loaded unbalanced system, is used in the study. The D-STATCOM consists mainly of a three-level inverter with IGBTs and PWM control. Modeling and simulations are implemented in Matlab/Simulink.

Improving the performance of protection schemes in three level IGCT-based neutral point clamped converters

High power IGCT-based converters are currently used in a wide range of drive applications. The protection of such converters against internal faults has been addressed in the technical literature, but the main focus has been on the solutions to disconnect the converter from the mains. In this paper, the short circuit current paths through the power devices in the three level NPC bridge are identified and studied from the perspective of keeping the overall repair cost, after a fault leading to the shoot-through mode, to a minimum. It is shown in this paper that a preferred short-circuit current path that limits the thermal energy in all IGCTs to safe levels exists. Furthermore, it is demonstrated that it is possible to guarantee, through proper busbar geometry and/or device selection, that the short-circuit current stress can always be moved to the power diodes. Simulation results are presented to support all the discussions and conclusions.

Thyristor Switched Series Reactor for Electric Arc Furnaces

Supplementary series reactors are widely used in high power AC electric furnace to allow furnace operation with longer arcs, lower currents and lower electrode consumption. Such reactors can be switched off in the final stages of the melting process when the electric arc is stable and arc ignition is not of great concern. Bypassing the reactors with the use of conventional high voltage circuit breakers is not practical due to the maintenance problems related to the great number of operations. This paper describes an oil-immersed thyristor switch with a proper design for installation at a high voltage industrial substation to switch on and off the series reactor of the electric arc furnace circuit in order to improve furnace productivity. The concept of Thyristor Switched Series Reactors, TSSRs, can also be used to minimize or even replace on load tap changing of the furnace transformer.