Abstract

Power transformers are essential elements in the production and distribution of electricity, and keeping them in optimum operating condition is a constant concern for specialists in the field. The condition of power transformers is mainly determined by the condition of the mixed insulation system, i.e. solid cellulose paper insulation and liquid insulating oil insulation. The identification method, described in this paper in order to determine the fault condition for power transformers is based on the fact that the assessment of their condition is mainly determined by the condition of the mixed insulation system, namely the solid insulation made of cellulose paper and the liquid insulation made of insulating oil. This is why the Three Ratio Technique (TRT) is used with good results for the early detection of power transformer faults. This method is considered as simple, but at the same time efficient in interpreting the results of dissolved gas analysis. It uses three new gas ratios to differentiate between thermal and electrical faults. In this paper, the ratios defined by the TRT method are used to train a machine learning classifier based on Ensemble Classifiers using Bagged Trees (random forest), Boosted Trees, and RUSBoosted Trees algorithms. The validation of the power transformer fault identification software application for the proposed method is carried out in the experimental section.

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Abstract

It is known that the use of synchronous motors in variable speed drives to simultaneously generate mechanical power and reactive power is among the most effective methods of improving the power factor in electrical distribution networks. Also, the adoption of automatic excitation control has expanded the application field of synchronous motors to handle high-load shock drives. Modern digital control systems designed for controlling the excitation of synchronous motors have revitalized the significance of these machines. This paper presents a synchronous motor excitation control system that provides a fully digital solution for the design of equipment to supply excitation and control the operation of high power synchronous motors. This system can be easily parameterized for low and medium voltage synchronous motor drives of various rated powers, with asynchronous starting capability. An application of the system to the realization of an equipment for excitation power supply and operation control of high power synchronous motors is also presented. The equipment was realized in prototype version and after successful laboratory tests it was successfully produced in series and used to build electric drives for ore mills using asynchronous motors of 2.93 MVA.

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Abstract

A rotor field quasi-oriented control algorithm for drive systems equipped with a low cost DSP system has been implemented and experimentally validated in this paper. The system is designed for induction motor traction systems. The control algorithm implementation was done for a dSPACE DS1103 prototyping board in the Matlab Simulink environment. The control algorithm principle is based on the assumption that the current system is oriented by the rotor flux and the real flux follows the imposed value. Therefore, the rotor flux estimation is no longer necessary as well as the flux control loop. This makes the control algorithm suitable for low cost industrial DSP applications. The drawback is given by the fact that the current projections on the dq axes cannot be regulated, the current control being done by means of the current phasor magnitude. The control system implementation was validated with  good results, in terms of current and speed regulation especially at variable mechanical load (such as track joints or switches), making this method suitable not only for low cost traction systems, but especially for railway vehicles.

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Abstract

The superiority of using field-oriented control in electric drive systems based on induction motor has been proven over the years. To increase efficiency, maintainability, reliability and dynamic performance, modern electric traction systems use induction motors. In this context, this paper is focused on the performance determination and analyzing of the rotor flux-oriented control with voltage control, on an induction traction motor, in order to its implementation. First, the control scheme and calculation fundamentals are presented. Then, after the entire system modeling in Simulink environment, the performance of the system in dynamic and steady-state regimes is presented by simulating the operation of a real traction motor at three prescribed speeds. Also, a specific phenomenon of electric locomotives, respectively the passage of wheels over the rail joints is taking into account. To determine the performances, the results obtained from simulating the acceleration process by prescribing a speed ramp, operating in steady-state regime and then electric braking with energy recovery were analyzed. In the paper, three situations are presented: the prescription of a low speed, about 20 % of the nominal speed, of the highest speed, about 160 % of the nominal speed and of three speed steps up to the nominal speed. The analysis of the results leads to the conclusion that there is a very accurate tracking of the prescribed quantities by the actual quantities controlled in the system. It is also highlighted that the peak current through the motor does not exceed its limiting value and the switching frequency of the power electronic devices is lower than the imposed limit value. The analysis of steady-state performance shows that it is also very good.

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ANNALS OF THE UNIVERSITY OF CRAIOVA – Electrical Engineering Series, no. 48, vol. 48, Issue  1, 2024 (click to download)

Abstract

This paper presents some experimental aspects related to the operation of asynchronous motors powered at variable voltage. A modern system for actuation of low-power asynchronous motors is presented, equipped with a voltage and frequency converter. Also, a data acquisition system is presented, with a sampling frequency of up to 100 kHz, supervised by an acquisition program that allows the visualization of the variations of the main characteristic sizes of the motor. The program contains both graphic interfaces developed by the manufacturer and by the authors of the paper. This program solves, among other things, an electromagnetic compatibility problem. The experimental tests carried out with the help of this system (in permanent non-sinusoidal regime at various power supply frequencies) are detailed. Technical details of the main system components are provided. The tests are accompanied by photos taken during the experiments and many original explanatory graphics. The authors’ contributions are mainly in the software area. Thus, in the original program, a series of windows for harmonic analysis and visualization of the characteristic phasors of the analyzed electrical quantities were implemented. The paper ends with the main conclusions resulting from the completion of the study and with a representative bibliography.

Abstract

Increasing the efficiency of photovoltaic panels using solar tracking systems is a current topic. The use of solar tracking systems is a solution, especially in low power applications. The paper presents two types of solar tracking systems, one based on astronomical data, and the other based on tracking the point of maximum illumination. Both systems are made on small scale for educational purposes. These systems can be used for the analysis of methods, principles and particularities in order to use them in practical applications. For the two experimental models of solar tracking made, the hardware and software structure are presented. To orient the photovoltaic panels in the two directions (East-West, respectively South-North) DC motors or stepper motors are used. One motor is used for each axis of rotation. Both structures have the control part composed of a microcontroller development system. This control method has the advantage that can significantly reduce the number of electronic components as well as the cost of designing and building of equipment. For the solar tracking system based on astronomical data, a remote monitoring and control system has been achieved. It uses a friendly graphic interface made on PC with the help of Visual Basic software. Both models were tested and the experimental results showed correct operation according to the imposed protocol. Finally, an energy efficiency analysis was done and it was found that the PV panel that uses the tracking systems produces 35% more energy compared to a fixed PV panel.

Abstract

In order to efficiently and practically solve the problem of analyzing the performance of the SCADA (Supervisory Control and Data Acquisition) system of the power grid, this paper proposes to reconfigure the graphical user interface (GUI) in the substation, as well as to remap the signals according to the hardware structure used. After replacing the hardware solution with PLC and software for protocol conversion installed on the local HMI with a specialized remote terminal unit for data storage and protocol conversion in the substations, it is important to adapt the graphical user interface of the SCADA system according to the latest hardware configuration. This is necessary for the stability and reliability of the SCADA system. In the last part of the paper, the configuration of the graphical user interface of a SCADA system and the remapping of the signals in the specialized software in an electrical substation in Romania is presented and highlighted through screenshots.

Abstract

The development of geolocation systems( geostationary satellite networks), as well as devices capable of receiving signals and processing the data coming from them, makes possible the implementation of location monitoring systems for various purposes. Whether it’s about security or optimizing travel times or routes, these systems are based on information in the form of global coordinates (latitude and longitude) from satellite systems or cell towers. The design of such a system is presented in this paper, being a good guide in the design and implementation of such a system, regardless of the application. Both, the hardware part (the designed equipment) and the software part (the backend component running on a virtual private server, as well as a mobile application) are presented in this paper. In the development of the system, was used only location provided by information from satellites, without using GSM cell signals. The entire system has been successfully tested in different GSM signal conditions as well as various locations to see the influence of environmental parameters on performance. The system described in the paper can be the starting point for the development of other systems for a variety of applications that require the management of the location of some devices.

Abstract

In order to realize an efficient synthesis of the control algorithm, it is necessary to be known the mathematical model of the control object. This paper deals with the problem of data-driven control of second order astatic inertial systems with, or without time delay, that supposes an experimental identification of the mathematical model in the closed-loop and algorithm for synthesis the PD and PID controllers. The control algorithm was synthesized according to the maximum stability degree method with iterations. The closed-loop identification method and control algorithms of the PD and PID controllers were verified by computer simulation in MATLAB and there are obtained good results in model estimation and in the tuning of the PD and PID controllers.