Journal of Operation and Automation in Power Engineering
Volume:10 Issue: 3, Autumn 2022

Improving the insulating and thermal properties of transformer oil is one of the factors in the use of nanoparticles (NPs) in oil. However, the use of NPs may only have a positive effect on some properties of the oil or even have a negative effect on the other properties of the oil. For this reason, hybrids nanofluid(HNF) were used to improve the properties of the transformer oil. By performing the Breakdown Voltage (BDV) test on different weight percentages (wt%) of TiO2 and CNT, it was proved that the best wt% for TiO2 is 0.0075 and for CNT is 0.001 to maximize the BDV. In this case, the HNF was able to improve the BDV and heat transfer by 9% and 8%, respectively. Another surprise that the HNF has been able to reduce the amount of C2H4 and C2H6 dissolved in oil by more than 70%. This reduction in the number of gases has another very desirable result and has reduced the PD by 63%. HNF proved that by using the right combination of different nanomaterials in transformer oil, more properties of the transformer oil can be improved.

This paper presents a new fuzzy direct power control of double-fed induction generators (DFIG) in the wind power system. The most important issue in the application of DFIG generators is proper control of the active and reactive powers of these generators, which are generally carried out by vector control or direct torque/power control methods. Direct power control (DPC) directly controls the active and reactive powers of the stator, and stems from results from direct torque control. To use the vector control method, it is necessary to use conventional PI controllers the main disadvantage being the controller robustness due to the nonlinear behavior of the wind turbine and blade oscillations, and it is unavoidable that after a while, the controller's coefficients need to be updated. Therefore, the main purpose of this paper is to present a direct power control method based on fuzzy construction to overcome the mentioned problem. Simulation results of the proposed strategy are extracted under different performance conditions, and these results are compared with the conventional vector-oriented control method. These comprehensive results exhibit the effectiveness of the proposed fuzzy DPC method for the DFIGs based wind power systems.

Many published studies debated electrical energy management. They mainly investigate the multi-source installation to develop energy efficiency during its different phases: production, distribution, and consumption. Although it is rarely discussed, energy sharing is a critical part of the energy management system. In this contribution, a demand-side management algorithm is developed, that incorporates energy consumption scheduler capacity. It provides optimal energy sharing, counting on suitable energy cost parameters and adequate multi-source installation. Using this proposal, the electrical bill decreases thanks to the optimal daily attribution of schedules to households formed by a multi-consumer microgrid. This application guarantees a maximal reduction of electrical cost for the set of energy partners as one prosumer used to consume and produce power. In addition, it maintains energy efficiency as it aids in avoiding breakdowns, and depressing the peak-to-average ratio. It admits that the utility company is, as usual, always reachable non-renewable source. At the same time, renewable energy was engendered by photovoltaic panels concomitant with wind turbines stations. The application is based on the JNET protocol stack. The proposed energy sharing algorithm is implemented by using Arduino board and JN5148 nodes as a star Wireless Sensors Network topology. It is installed as a prototype in the Digital Research Center of Sfax in Tunisia.  This proposed incentive-based algorithm managed to reduce the smart microgrid annual cost by almost 55% without harming the public utility. It can even ensure a more significant diminution by selling the surplus of renewable power at the end of each day.

Nowadays, renewable energy sources are considered better choices in the field of energy generation. It is possible to replace traditional energy sources (i.e., petroleum oil and gases) with more attractive alternatives. This presents several advantages, such as low emissions of greenhouse gases and reduction of climatic change along with associated global warming. In the current paper, a comprehensive review is done introducing thermoelectric generation (TEG). These are applications of renewable energy sources that use the Seebeck effect to generate electricity. In this type of system, two different materials melt at their ends. One is on the hot side, while the other is used as a cold side. The present paper is a survey that includes applications and hybrid systems (based on renewable energy sources) that are integrated with a thermoelectric generator. Also, investigations of the effects of including thermoelectric generation in hybrid systems on the overall performance of such systems are reviewed. These systems can be viewed as an investment in recovery of waste heat from devices such as water pipes, photovoltaic panels, and vehicle exhaust to produce extra power in a hybrid system.

The Lightning Impulse (LI) test is performed on newly manufactured power transformers as a routine Factory Acceptance Test (FAT). A well-known Marx Impulse Generator (MIG) is utilized in this test. The setting of the MIG can be changed to obtain standard LI wave shape. Since various power transformers may have windings with dissimilar designs, different MIG settings may be required for each transformer. The accurate computer simulation of the LI test circuit can give help in finding the optimum setting of the MIG. The Frequency Response (FR) of the power transformer impedance is required in such simulations. Similarly, the transformer FR is required in calculating the Transient Recovery Voltage (TRV) across the contacts of the Circuit Breakers (CB) in the case of the Transformer Limited Fault (TLF). The accurate calculation of such TRVs has a great importance in selecting the proper rating for CBs. The FR of the transformer can be measured directly with network analyzers or some other conventional test instruments. However, performing an additional test to obtain the transformer FR imposes extra cost and efforts. Alternatively, it can be achieved by using the routine LI test results which is readily available. Fortunately in both mentioned applications similar connections are required for transformer terminals. In this paper, the procedure to extract the transformer FR using the LI test results is presented. Then, the validity of such extracted FRs is investigated by comparing them with the ones measured by conventional test instruments. As an innovation, the extracted transformer FRs are used in the LI test circuit simulation and the accuracy of the method is examined by experimental works. Moreover, the application of the extracted FR in TLF TRV calculation is investigated as well. The validity of the all presented theoretical concepts are evaluated using the experimental test results on a real large power transformer.

In this paper, quadratic convex relaxation (QCR) is used to relax AC optimal power flow (AC-OPF) used for reactive power scheduling (RPS) of the power system. The objective function is system active power loss minimization to optimally determine the tap position of tap-changers, the reactive power output of generating units, synchronous condensers, shunt capacitor banks, and reactors. The nonlinear and non-convex terms due to trigonometric functions cause the problem to be non-convex which results in trapping in local minimum or even not converging in large size power systems. Therefore, in this paper, the nonlinear terms and trigonometric function are relaxed by linear and quadratic functions. Furthermore, the product of two variables and multi-variables are relaxed by McCormick bilinear and multi-linear expressions, converting the AC-OPF of RPS to quadratic constraint programming (QCP) optimization problem. The proposed RPS method is studied based on IEEE RTS 24-bus test system. The results show the accuracy of the proposed (QCR) method to relax the AC-OPF optimization problem of RPS.

The main goal of the paper is to achieve the structural reliability of the failure components in the system that can be modelled as a Transfer Function (TF). The classical reliability of the power system has been a major field for research in the past decades, which has resulted in the reliability of the power grid by integrating the failure rates of the system components. As a result, a gap analysis is carried out by modelling the failure components into TF, and a comparison of structural and classical reliability is explained in the paper. The paper expands on methodology of the mapping technique for transforming a system from one domain to another. By doing so, the transformation of the Complex Coefficients Integer Order (CCIO) and the Complex Coefficients Fractional Order (CCFO) system transfer function becomes the Non-complex Coefficients Integer Order (NCCIO) in nature. Therefore, the root locus plot for the transformed system is observed as the symmetrical structure about the real axis. Therefore, the plane transformation becomes advantageous in the field of structural reliability analysis. The root locus plot for the transformed system into a w-plane becomes reliable as per the symmetrical structure. The reliability index Loss of Load Probability (LOLE) has been evaluated with different forced outage rates of the system components to analysis the classical reliability of the system.

Power equipment are subjected to multiple shock voltages during their operations that are generally caused by a lightning strike, switching of electronic power devices, or transient voltages which across available in the power system. These impulses have a frequency range from several kHz to several MHz, which take pulses at very short intervals in several microseconds. Also, the equipment experiences the peak voltage and subsequently peak currents than their nominal values. These variations in voltage and current values, in very short intervals, have destructive effects on these equipment insulated systems as well as on the accuracy of measuring ground impedance. The primary purpose of this study is to investigate the effect of standard and non-standard voltage impulse on power transformers windings by considering the mutual induction of transformer windings. Furthermore In this paper, by applying lightning pulse on power transformer windings for different models of ground voltage distribution system on different disks of transformer windings terminal (20/0.4KV, 100KVA, 9 disks continuous winding) and the disks voltage are calculated as outputs in MATLAB/Simulink. In previous studies, the calculations were in the time domain, while in this study, the ground impedance was measured in the frequency domain. The simulation results show that considering the model RC and considering the mutual induction, the voltage distribution on the disks is higher than other models. This study provides functional information for improving the design of insulations that are installed between windings and core the results of the present research may lead to the minimization of the dielectric failures. Furthermore, the results of this study can be used in future studies about non-standard impulse voltages. This investigation can certainly lead to modifying available standards or creating new standards in power transformers.