Mircea Ion Buzdugan

Series Resonance Technique for Short-Circuit Current Limiting Devices in DC Grids

The paper presents a by-pass solution used to limit the short-circuit current in the DC networks. The aim of the by-pass circuit consists in injecting a reverse current throughout the power switch, in order that switching achieves at low current value. The reverse current generation is obtained using a series resonant circuit, simulated in the paper in the Matlab-Simulink medium, the results of the simulation being compared to the experimental ones.

Considerations on Electromagnetic Compatibility for Medical Devices

The paper deals with the electromagnetic compatible design of medical products, starting from the early stage of the design process (the prototype stage). This way of thinking is presented for the case of one kinetic therapy equipment. In the functional block diagram of the equipment are pointed out the main electromagnetic interference paths. The specific test setup and measurements in accordance with the European conducted immunity standards for electromagnetic compatibility are presented. Two kinds of measurement were performed: inter-system measurements (to the mains supply port) and intra-system measurements (to the printed circuit board and the internal cables). Several solutions for mitigating electromagnetic interference problems which greatly improved the electromagnetic immunity of the equipment are also depicted. The main conclusion which must be drawn from the present paper is that designing for electromagnetic compatibility is the most energy saving and cost effective policy.

Modeling and simulation of DC resonant circuit breakers

The specific problems of the disconnection of HVDC breakers need an analysis of performances at laboratory scale. In the study of hybrid circuit breakers with commutation, three steps are necessary: modeling, simulation and experimental tests. The paper presents a modeling procedure for a hybrid commutation breaker intended to operate using resonant circuits phenomenon. Using the Matlab platform, the simulation of the disconnection of short-circuit process, highlights the reduction of the disconnection period at a low value of the short-circuit current. The performance of the electric equipment is analyzed in the laboratory, in terms of the concordance between the model and the simulation procedure.

Electromagnetic compatibility issues of brushless speed drives

The paper presents the assessment of electromagnetic compatibility of adjustable drives used in residential air conditioning systems (i.e. air handling units, systems that conserve a significant amount of energy, while maintaining indoor comfort) with a particular stress on brushless DC motors. In the introductory section, a recall of the new smart power modules, that drive centrifugal fans provided with brushless DC motors are briefly depicted. Next, the main operating principles of air handling units are shortly addressed, along with detailed test setups and results obtained on conducted electromagnetic interference and electromagnetic conducted immunity, according to electromagnetic compatibility standards, compulsory for air handling units. The main conclusion of the paper is that even if electromagnetic compatibility tests are quite tedious and time consuming and particularly more often neglected, they have to be a permanent concern from the early stage of design, in order to save other resources which would be involved with certitude afterwards, in the final stage of a project.

Diagnosis of short circuit and the earthing of a transformer station

The paper presents the monitoring of the power quality of an underground electric line fed by a high voltage transformer station 110/10 kV and a subsequent earthing fault situation followed by a short circuit. The monitoring process was performed using a power quality analyzer. The analysis of the evolution in time of the phenomena highlights the variations of the voltage in the medium voltage bus of the transformer station during the failure situation.

Performances of the anti-perturbation filters for current distortion factor reduction

The paper presents a few aspects of power quality at the supply port of power electronic converters. The main point is that the lack of power quality, especially in the case of a large harmonic content, leads to conducted electromagnetic interference. The approach focuses mainly on the methods of assessing conduced electromagnetic interference. At the same time the methods of testing in laboratory conditions of the insertion loss of EMI filters are depicted. Experimental results of mitigating conducted electromagnetic interference using EMI filters along with their efficiency are also presented.

Performances optimization and characteristics of the voltage generated by multilevel inverters

Several fixed frequency applications of multilevel converters require a very low level of distortion factor of the output voltage. Bringing the output voltage to a form as close as possible to a sine wave is usually done through linearization methods of the Newton-Raphson algebraic equations. The method proposed in section III uses for the waveforms optimization a genetic algorithm, having a positive impact on the total harmonic distortion reduction. Experimental validation of the method is performed using a programmable source which drives an induction motor.

Wavelet analysis in monitoring and diagnosis of power circuit breakers

Monitoring of electrical equipment is a direction of current development in the maintenance domain. The method aims to establish the operation state of the monitored equipment. Fault diagnosis existing on power circuit breakers is very important aspect in emergency situations, when it must be interrupted by high current circuit breakers. This paper presents a model of vibration monitoring using Wavelet-Morlet transform. Here are reviewed theoretical problems of using Wavelet-Morlet transform, signal processing techniques and experimental results that highlight the difference between faulty equipment and one in a proper working condition.

Fault Identification on Electrical Machines Based on Experimental Analysis

The paper reviews the main faults identification of electric machines based on amplitude versus time and amplitude versus frequency vibration analysis. The aim of the paper is to introduce a new method in determining rotor faults based on stator vibration. The analysis method uses a multi-channel vibration analyzer provided with three accelerometers, set in a plane perpendicular to the stator axis. The method is suitable for determining rotor faults generated by the stator vibrations, other than those due to current harmonic components or supply voltage unbalance. The SvanPC software allowed the determination of the characteristics regarding velocity vibration versus time and versus frequency. Their interpretation permitted to determine the fault points on electrical machines in two industrial applications.

Design and Test Procedures for EMI Filters Used for Nonlinear Loads

This paper analyzes an EMI filter solution to diminish the effect of harmonics generated by PWM converters in active filters. Throughout this paper, we have presented specific problems regarding the design, simulation and the validation of the model by testing EMI filters. It can be mentioned that the tests of the experimental model were performed in a laboratory, using existing conditions for the non linear consumer, by generating distorted waveforms.