نشریه عصر برق
پیاپی 18 (زمستان 1401)

The survival of modern human life today depends on energy security, any interruption, e.g., by solar sources that cause various disruptions in the power grids. Special attention has been widely paid to studying the electrical disturbances following the March 1989 event in northern Canada. For this purpose, various countries started several studies to take the necessary measures to reduce the damage caused by geomagnetic storms in the power network. We carefully know that solar activity was considered the principal source of geomagnetic storms. Coronal mass ejections- the huge bubbles of hot plasma and magnetic fields with a speed of about 200 to 1000 kilometers per hour and solar flares are the most important causes of a geomagnetic storm. If they occur toward the Earth simultaneously, they can affect Earth’s magnetic field and cause significant disturbances in the power grids. The solar activity has 11-year periods, but it is not entirely possible to predict the occurring time of solar events. Temporal variations of these currents cause a geoelectric field and low-frequency quasi-static geomagnetically induced currents (GIC) in power grid equipment. Studies in different geographical locations show that the magnitude of geomagnetic induction current (GIC) is directly related to the temporal changes of the disturbing magnetic field and especially to its horizontal component.
Transformers are one of the most effective equipment in a geomagnetic disturbance. In high latitudes, damages to power transformers have been reported in which geomagnetic changes during hurricane times have been very rapid and large (greater than 1000 nT), and hence GICs as large as or greater than 100 amps flow at the end of the storm in the winding. Usually, the geomagnetic disturbances are not strong at low latitudes, so much smaller GICs are reported there. However, the flow of GICs and their effects on power transformers are complex processes, and careful evaluation is required even in such low latitude regions. The strategies used against geomagnetic disturbances highly depend on geographical areas.
Countries that have already experienced the harmful effects of geomagnetic disturbances perform better in an event. Researchers in Russia, Japan, and Brazil proposed algorithms usable in all power grids and any geographical location. Testing the algorithms on the power grids in the mentioned countries confirmed that the magnitude of GICs and their possible harmful effects also depend on the power network topology, resistors, and other engineering details of the power system.
This article reviewed the impressive factors causing geomagnetic disturbances via solar activity and their effects on the power grids. In the logical next step, we will focus on finding the possible hazards in the Iranian bulk power network as linked with several neighboring countries by analyzing the related data.

Resonance in transmission lines can cause unusual over-voltages and put the equipment at risk. One of conditions that can lead to resonance in transmission lines is the asymmetrical connection (single-phase and two-phase) of transmission lines compensated by shunt reactor. The asymmetrical connection of the line can be caused by the failure of the circuit breaker, activation of the single-phase recloser, or the presence of switchsync relay. In this paper, the feasibility of resonance in the 400 kV Abu Talib-Torbat Jam transmission line is investigated using EMTP-RV software. According to the results, in the case of asymmetrical connection (single-phase and two-phase) of the Abu Talib-Torbat Jam transmission line, resonance does not occur in the power frequency. But this line has a resonant frequency in the range of harmonics. In order to investigate the effect of harmonics, harmonic studies have been conducted and it is shown that harmonics cannot cause unusual over-voltages in this line.

Due to the significant growth of load in the power industry as well as the high penetration of wind turbines (WTs) in power systems, the issue of unit generation (UC) planning has become a critical issue. UC determines the problem of planning the production of units, the time when units are turned on and off, and how to distribute the load between the units that are turned on so that the cost is minimized; Therefore, the main focus of this article includes two scenarios that examine the production planning of units with different constraints, including the slope rate and the production prohibited area in the presence and absence of WTs; Therefore, at first, the production planning of the units is done by considering the load of future hours, which increases the reliability of the planning and also minimizes the costs. In the second part, a method for planning the production of units is presented, in this method, the minimum shutdown time of the units is also included in the objective function, in fact, the start-up costs are considered hourly. This proposed method changes the production planning pattern so that the costs are reduced. Finally, the implementation of the problem is done in two scenarios considering wind turbines and the absence of wind turbines.

With the increasing penetration of DG resources in distribution systems, the performance of these systems has changed from passive to active mode and the possibility of two-way power exchange between the main network and the distribution network has been provided. The use of DG resources in the distribution system has economic-technical advantages if their installation location and production capacity, which are influenced by the working mode (the ability of DG to exchange both active and reactive power components) and the control strategy used in the converters, be optimaly selected. In this article, a method will be presented to solve the placement problem and determine the optimal capacity of DG resources (OPSDG) in distribution networks, in which the load flow injection model is used to model DGs and the working state of the resources is also considered. This model minimizes the influence of the control strategy of converters on solving the problem. In the method discussed in this article, the objective function is a weighted combination of voltage profile indicators and power loss reduction. To optimize the objective function, the enhanced algorithm of particel swarm optimization algorithm is presented. The enhancement of the algorithm will be done through the use of crossover and dynamic mutation operators for the set of particles. The simulation results show that under the strategy presented in this article, the voltage profile and active power losses will be in the optimal state.

The significant growth of kidney disease, its effects and complications, and the costs that are imposed on the society, have caused the medical community to look for programs to predict and diagnose this disease early. In recent years, the use of data mining techniques in the field of medicine has gained great importance. The purpose of this article is to review methods based on data mining techniques in order to predict chronic kidney diseases. In this article, it is intended to collect and review a comprehensive review of chronic kidney disease, diagnosis methods in the field of medicine.  In this paper, chronic kidney diseases were examined first, and following this examination, we will discuss and analyze the field of early diagnosis of these diseases. In the following, we will introduce various data-mining algorithms in the diagnosis of chronic kidney diseases. After that, we will discuss the methods of diagnosing and predicting chronic kidney diseases, and we will review these methods in terms of their goals, limitations, and capabilities. In this article, in order to predict the failure disease, all the different points of view, which are: feature selection, classification method, used tools, are examined, which we show by analyzing the classification algorithms. The use of random forest algorithm, k-nearest neighbor algorithm and support vector algorithm along with feature selection methods can play an effective role in predicting kidney failure disease. Also, the results show that the UCI database and MATLAB tool are the most useful in diagnosing and predicting chronic kidney diseases.

One of the most used methods for exploiting wind energy is the use of wind turbines, these turbines are used to generate electricity. They use different electric machines, and among these machines, the two-way induction generator has a greater share due to its advantages.In this article, a direct power control method based on fuzzy controller for wind turbines equipped with DFIG generators is presented.In this method, the required voltages of the converter on the rotor side are calculated directly based on the phase controller, stator voltage, rotor speed and some machine parameters.
On the other hand, PWM modulator has replaced hysteresis comparators. In this presented method, the switching frequency is fixed. The simulations for the presented method have been done in steady and transient conditions

Nowadays, microwave imaging, as an emerging technology, plays an important role in the detection and characterization of targets in many fields, including civil engineering, industry, geology, and medicine. In this paper, with an emphasis on microwave medical imaging, we will review and introduce leading academic and commercial systems in the field of breast cancer diagnosis and brain complications. The basis of microwave medical imaging is the difference in the dielectric properties of different body tissues in the microwave band. In this paper, we will introduce and examine 9 prominent research groups and 5 commercial companies active in the field of microwave medical imaging. The results of clinical studies of the mentioned systems indicate the optimal sensitivity and reliability of microwave imaging in detecting unhealthy masses, both in the breast tissue and in the head.