Applied Mechanics and Materials Vols. 799-800

Abstract: Compensation of a voltage within the appropriate range becomes difficult when a large number of photovoltaic (PV) systems are installed. As a solution to this problem, the installation of a low-voltage regulator (LVR) has been studied. In this paper, we propose a method for instantly and accurately determining the line drop compensator (LDC) method parameters as a part of a voltage management scheme, which consists of prediction, operation, and control. In the proposed method, the solution candidates of the proper LDC parameters are narrowed by using a random forest that learns the relationship between the power-series data and the properness of the LDC parameters, thereby reducing the computational cost. We performed numerical simulations to verify the validity of the proposed method. From the results, the LDC parameters can be rapidly and accurately determined. Additionally, the desirable voltage control performance is verified.

Abstract: The disadvantage of Beijing-Tianjin-Tangshan power grid operation control mode is that the control effect is poorer and the spare capacity demand is big, this paper puts forward a new coordinated control strategy. First of all, this paper describes the relationship between the load, frequency, the output of generating unit, the tie line power and the area control error relationship of the whole power grid, according to the regional automatic generation control performance assessment criteria, concludes the characteristics of regional unit adjustment. This paper analyzes the contradiction between them, and then proposes a coordinated control strategy between the Beijing-Tangshan power grid and Tianjin power grid. The case simulation results prove the superiority and feasibility of the new coordinated control strategy. Compared with the original, the new strategy reduces the volatility of the unit, shortens the recovery time of frequency, and has a certain practical significance.

Abstract: Our aim is to show some impacts on the differential protection of power transformers when using Non-Conventional Instrument Transformers associated with the IEC 61850-9-2 process bus. Described herein are a model for simulating the samples in the process bus, a proposed algorithm for differential protection of power transformers adapted from conventional differential relays so that it works according to the IEC 61850-9-2 standard, and a response analysis of the protection algorithm with the loss of the time synchronization signal in the process bus. Suggestions on parameters to be followed for safer operation of the process bus in these circumstances are also offered.

Abstract: The method of dielectric spectroscopy is an instrument of choice for the diagnosis of insulation used in high voltage and also to assess the quality of the insulation of HV equipment such as transformers, cables, capacitors, etc...This method allows to estimating the state and the quality of the insulation using the dielectric response of the frequency range. In this article, we have presented results of dielectric studies in high-density polyethylene (HDPE) by means of dielectric relaxation spectroscopy (DRS) in frequency range 10^-2 - 10⁶ Hz and temperature between-60 and 60 °C, we will invest this method to measure the dielectric properties and evaluate the performance of this insulator witch has always been chosen as a model polymer material because it is the simplest polymer with respect to its chemical structure and is used in a wide range of applications in daily life.

Abstract: The paper presents the instrument for measurement of transfer ratio voltage transformers in the frequency range. The instrument distinctive feature is measuring of small differential signal of the voltages with sensitivity 2 nV against the background of large common-mode signal. The instrument features, its technical and metrological parameters are also considered.

Abstract: The description of hysteresis is one of the classical problems in magnetic materials. The progress in its solution determines the reliability of modeling and the quality of design of a wide range of contemporary devices, as well as devices that will be created in the future. The intensive investigations in hysteresis modeling were induced by the fact that accuracy models of magnetic hysteresis must be studied yet. In this paper, several identification procedures of the distribution functions of the Preisach model will be investigated by means of a genetic algorithm.The proposed approach has been applied to model the behavior of many samples and distribution functions are optimized which will give accurate results of the hysteresis loop. The results show the robustness and efficiency of genetic algorithm to model the phenomenon of hysteresis loop. This work can give solutions about the ferromagnetic material evaluations and shows the optimization of distribution functions according to the material behaviors.

Abstract: Robust control analysis using Gerschgorin theorem is an important tool for the research of linear uncertain system which is expressed in state space form. The main purpose of this paper is to show how this technique can be applied for robust stability analysis of dc-dc converters. In this paper, robust stability analysis of dc-dc Buck converter is presented using Y. T. Juang and C. S. Shao criterion. This criterion is based on Gerschgorin theorem and similarity transformation.

Abstract: The failure of large generators in generating stations and industrial plants is mainly caused by the failure of the stator winding insulation. The combination of electrical, mechanical and thermal stresses that are accumulated by the number of start-stop times and operating hours can reduce the residual dielectric voltage as the main cause of the deterioration on the insulation. In this study, the remaining life assessment of the generator stator insulation was conducted based on the functional relationship between stresses and remaining dielectric voltage in the worst and average cases. The case study was conducted on the fourth of generator unit in SURALAYA Coal Fired Power Plant in Indonesia that had the service life of over 25 years. To validate the assessment results, partial discharges (PD) test was performed on the stator coils of the generator. Based on the results of evaluation, it was found that the remaining life of the fourth of generator insulation at the worst case had been come to end. For the average case, the remaining life of insulation for Unit 1 and Unit 2 was 12 year, while for Unit 3 and 4 was 17 year. Then from the validation results using the PD test, there was an evidence of the discharging of voids or delamination within the insulation, where the internal discharging was seen to be the most dominant factor from the discharge pattern. However, the PD magnitudes were still within reasonable limits, where the magnitude of the maximum discharge was 3,500 pC for the U phase, while in the V and W phase was 7000 pC, hence it was not categorized as an anomaly.

Abstract: This paper deals with experimental verification and performance analysis of permanent magnet synchronous generator (PMSG) for wind power generation considering magnetic losses using d-q axis model. The d-q voltage equation of the PMSG is derived. The equations for losses such as copper loss, core loss and mechanical loss are also derived. Finally, by implementing dynamic simulation block diagram for the prediction of generating performance considering losses using MATLAB/SIMULINK, the generating performances of the PMSG are predicted under various speeds and loads. The predicted results are validated extensively by finite element (FE) analyses and measurements.

Abstract: One of the considerations many power plants today is whether they can get more power out of their existing equipment especially generator. However, it is required design review and feasibility study in order to extend the operating life and increase the capability and reliability. In this study, analysis of magnetic field was performed due to power uprating in order to prevent a saturation of the magnetic field in the core laminate which can lead to the emergence of heat concentration. Based on the results of magnetic analysis using finite element, there are no saturation of the magnetic field in the core lamination which can lead to the magnetic saturation and heat concentration, both for existing and uprating conditions.Therefore, the increasing a design margin on the generators from the current design of the margin of 471,000 kVA to 494,550 kVA with the 0.85 power factor will not pose a problem as long as all of the following recommendations can be implemented. Although it is predicted, there will be no saturation and hotspots on the generator, but the risk of temperature rise due to the uprating should be reduced by replacing the stator winding using the Full Class F Insulation which is resistant to temperatures up to 155 °C.