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)