Integration of photovoltaic power plants to the distribution grid has always been more desirable for both the investors and the grid operators regarding its significant advantages including less grid connection costs as well as the reduction of expansion needs in the transmission grid. However, taking into account the considerable capital expenditures of PV power plants and dependence of their generations to the climate conditions, it is necessary to thoroughly assess the potential regions for distribution grid integration of these power plants. In this paper, the photovoltaic potentials of Zanjan and Qazvin provinces in Iran are studied from both technical and economic viewpoints. A number of sites in various parts of the area under study are taken into account and simulations are performed through the PVsyst software for a detailed distribution grid-connected system using the metrological data and related loss factors. In addition, economic assessments are performed by means of levelized cost of energy (LCOE) index. The results of this paper reveal a proper potential for installation of distribution grid connected photovoltaic power plants in most of the studied sites especially in those located in south half of Zanjan and Qazvin provinces. Moreover, it is observed that the levelized cost of energy among the studied sites varies up to %13.5, which demonstrates the importance of proper site selection of PV power plants for reduction of investment costs.

With the worldwide increasing penetration of renewable power generations, their curtailment rate has also increased owing to several reasons including the lack of transmission capacity, grid congestion limits, and surplus generation during low load hours. Green hydrogen and Power-to-Hydrogen (PtH) units play an important role in the reduction of renewable power curtailments as well as the reduction of power grid total costs. It is the purpose of this paper to investigate the reduction of renewable generation curtailments via employment of PtH units. Candidate wind farms and PtH units are applied to the modified IEEE 24-bus power system in a 15-year planning scope with an annual load rise of %2. The MILP problem is solved in GAMS software via Gurobi solver and four cases are taken into account based on the hydrogen bid variations and the curtailment penalty changes. It is observed that without utilizing PtH units, there are large amounts of wind power curtailments. However, in the presence of PtH units, the annual curtailments are decreased significantly. Moreover, both the hydrogen bid as well as the curtailment penalty effect the curtailment reduction of renewable-based generations. The higher the hydrogen bids and curtailment penalties, the more the curtailment reductions.

Integrated electricity and gas systems (IEGS) with power-to-gas (PtG) units, as novel sector coupling components between electricity and gas systems, have been considered a promising solution for the reliable and economic operation of the integrated energy systems which can effectively reduce the challenges associated with the high penetration of renewable energy sources (RES). To confirm the economic viability and technical feasibility of the IEGS, its coordinated planning will play a crucial role. The more comprehensive the modeling and evaluation of IEGS planning studies are, the more precise and practical the results obtained will be. In this paper, an in-depth and up-to-date assessment of the available literature on the IEGS planning is presented by addressing critical concerns and challenges, which need further studies. A vast variety of related topics in the IEGS planning, including the impact of costs, constraints, uncertainties, contingencies, reliability, sector coupling components, etc., are also reviewed and discussed. In addition, the role of PtGs and their impacts on the coordinated IEGS planning are reviewed in detail due to their crucial role in increasing the penetration of RES in future energy systems as well as limiting greenhouse gas emissions. The literature review completed by this paper can support planners and policymakers to better realize the bottlenecks in the IEGS development, so that they can concentrate on the remaining unsolved topics as well as the improvement of existing designs and procedures.

Transient stability improvement of power systems in the event of short-circuit faults has always been an important issue in power systems analysis and studies. Resistive-type superconducting fault current limiters (RSFCL), owing to their capability in restricting fault currents, have been often taken into account as an efficient method to improve the transient stability of a power system. Regarding technical constraints as well as economic concerns, optimal allocation and sizing of RSFCLs in a power system play a crucial role in their efficient utilization. This paper aims to continue the authors’ previous work and enhance the transient stability of power systems by proposing an optimization approach for optimal sizing and the allocation of various candidate numbers of RSFCLs, as the most employed type of SFCL and the most efficient one in transient stability improvement. To solve the optimization problem, a PSO-based algorithm is solved in MATLAB through an objective function and related constraints. The efficacy of the proposed algorithm is evaluated by numerical studies on the IEEE 39-Bus New England system in various scenarios through the assessment of critical fault clearing time (CCT) as well as the generators rotor angle deviations as two crucial criteria for the transient stability of power systems. Simulating the optimization results in DIgSILENT Power Factory indicates an evident enhancement of the power system transient stability via employing optimized RSFCLs resulted from the proposed optimization algorithm. Moreover, the level of transient stability enhancement highly depends on the number of optimized RSFCLs employed in the power system. The results of this paper present a helpful guideline for power system planners to select an appropriate stability scheme based on RSFCLs besides other related technical and economic issues.

Considering the importance of the transmission lines, it is crucial to protect them against different faults. The distance relay has been used as the main protection of power transmission lines for many years due to its simple operation and convenient protection coordination features. Despite its many advantages, the distance relay has two main problems that make its use challenging. One of these factors is the operating time of this relay and the other factor is the possibility of making wrong decisions when a power swing occurs. In order to reduce the operating time of the distance relay, in this paper, the use of the Flat-Top signal window is proposed. A new method based on the impedance difference measured by the Rectangular and Flat-Top signal windows has also been proposed to detect power swings and distinguish between power swings and faults. The proposed new methods have been tested on the IEEE standard 39-bus network using DIgSILENT and MATLAB software as well as a laboratory system. In both evaluation modes, the operating time of the distance relay in the proposed Flat-Top window has been compared with other available signal windows, including Rectangular, Bartlett, Blackman, and Blackman-Harris. The results clearly show that the proposed window creates the shortest operating time in different conditions (noisy, no noise, and CT saturation). Therefore, this signal window is introduced as the most suitable choice for use in distance relays. The simulation results also show the excellent performance of the proposed power swing detection algorithm in different conditions.

The use of renewable-based resources, such as wind energy, for generating electrical energy has been growing in recent years due to several reasons including free and infinite resources as well as their considerable impact on the reduction of fossil fuels consumptions and CO2 emissions. It is the purpose of this paper to investigate the effect of grid-connected large-scale wind farms in a region in Iran, on the reduction of natural gas consumptions in heat-cycle power plants and their related CO2 emissions as a practical case study. The wind farms under study comprise about 51% of the total grid connected capacity of wind generation in Iran. First, the total energy yielded by the considered wind farms are extracted for a two-year period from April 2019 to March 2021 based on a detailed practical data and then, the impact of this renewable-based energy generation is studied on the reduction of natural gas consumption in a real gas-cycle power plant due to its practical fuel intake data. The financial revenue of savings in the natural gas intake is also estimated based on the two-year average international price of natural gas. Finally, the reduction of CO2 emission is calculated as the result of reduction in the natural gas consumption of the considered gas-cycle power plant. The results of this practical case study well demonstrate the effective role of wind farms energy generation on the reduction of fossil fuels consumption in heat-cycle power plants and thus, the significant reduction of CO2 emissions as one of the most crucial aspects of decarbonization plans.

Background and Objectives: Smoking is a hazardous habit with numerous adverse effects on oral health. It plays an important role in development of cancerous and precancerous lesions and periodontal disease. Saliva has an antioxidant system and several enzymes. This study aimed to assess the salivary levels of uric acid (UA), lactate dehydrogenase (LDH), and amylase in smokers versus non-smokers. Materials and Methods: This descriptive, cross-sectional study was conducted on 60 individuals (30 smokers and 30 non-smokers) at the Dental School of Islamic Azad University. The participants were requested to refrain from smoking, eating and drinking prior to saliva sampling. A minimum of 1 cc of unstimulated saliva was collected from each participant by the spitting method. The level of salivary LDH was measured by the DGKC method, the level of UA was measured by the uricase assay, and the level of amylase was quantified by the kinetic photometric method. Data were analyzed by t-test, Chi-square test, Fisher’s exact test, and Mann-Whitney test (P<0.05). Results: The salivary level of UA was 1.35±1.2 mg/dL and 1.08±1.05 mg/dL in smokers and nonsmokers, respectively with no significant difference (P=0.08). The salivary levels of amylase and LDH were 44509±38062 U/L and 420±244 IU/L in smokers and 47299±29659 U/L and 538±350 IU/L in non-smokers, respectively, with no significant difference (P>0.05). Conclusion: Despite the slightly higher level of salivary UA in smokers, the difference between smokers and non-smokers was not significant in any of the tested parameters.

This paper investigates the ability of large scale wind farms in damping improvement of inter area oscillations in power systems. Considering the increasing penetration level of wind farms in power systems, their contribution in damping improvement of oscillations will be of great importance. The purpose of this paper is to employ the synchronverter control model for wind farms in order to enhance the inter area oscillations. To perform required simulations, the wind farm as well as its controllers are thoroughly modeled in DIgSILENT Power Factory using DSL programming. The Kundur two-area test system is utilized for time domain simulations to demonstrate the capability of wind farms with synchronverter control models in damping improvement of inter area oscillations. Simulation results reveal the suitable performance of the investigated method in the event of various disturbances including short circuit faults and mechanical torque variations of synchronous generators.

Electricity generation through renewable energy sources such as wind energy has been growing in recent years due to several reasons including free and infinite resources as well as their considerable impact on the reduction of fossil fuels consumptions as well as CO2 emissions. This paper aims to assess the impact of grid-connected large-scale wind farms in a region located in Iran, on the reduction of natural gas as well as gasoil fuel consumptions in heat-cycle power plants and their related CO2 emissions as a practical case study. The wind farms under study comprise about 51% of the total grid connected capacity of wind power generation in Iran by the end of March 2021. The total energy yielded by the studied wind farms are first extracted over a two-year period from April 2019 to March 2021 based on a detailed practical data and then, its impact is investigated on the reduction of natural gas and gasoil consumptions in a real heat-cycle power plant due to its practical fuel intake data. Finally, the reduction of CO2 emission is calculated as the result of reduction in the natural gas and gasoil consumptions of the considered heat-cycle power plant. The results of this practical case study well demonstrate the effective role of wind farms energy yields on the reduction of fossil fuels consumption in heat-cycle power plants and thus, the significant reduction of CO2 emission as one of the most crucial aspects of decarbonization and fossil fuel phase out plans.

Background and aim: reduction of dental plaque pH is an effective factor in the incidence of dental caries. One of the common methods for assessment of the cariogenic potential of food products is the study of plaque pH changes in the oral environment. The present study was performed due to the importance of dental plaque and its known complications and also the increase in consumption of industrial fruit juices which are encouraged nowadays as healthy drinks and also the positive effect of pomegranate juice on the amount of dental plaque which has been mentioned in the reports. Materials and methods: This clinical trial was performed with crossover design. Complete prophylaxis was performed during the first session. Then, the participants were asked to refrain from oral hygiene methods for 48 hours and not to eat or drink for at least 2 hours before the experiment. The baseline plaque pH was measured, and afterwards 10 cc of fruit juice was kept in mouth for 2 minutes and then swallowed. Afterwards, plaque pH was measured at time intervals of 2, 5, 7, 10 and 30 minutes. After one week of wash out period, the participants were again evaluated by the same method and with the other type of fruit juice. The measurement of plaque pH was performed with microtouch method by use of Metrohm electrode. The data were analyzed by repeated measures ANOVA. Results: pH in pomegranate juice group before fruit juice intake equaled 6.73± 0.24 and reached 5.57±0.34 at the fifth minute and finally reached 6.19±0.32 at the 30th minute (p˂0.01). Also, in orange juice group, pH before intake equaled 6.16±6.8 and reached 5.62±0.17 at the seventh minute and 6.15±0.2 at the 30th minute (p˂0.01). The maximum fall in pH for both fruit juices occurred at the fifth and seventh minutes. pH after consumption of both fruit juices began to increase from the tenth minute. These two fruit juices were not significantly different regarding plaque pH at the zero minute and at the time of maximum pH fall and at the 30th minute. (p˂0.08) Conclusion: The results showed that plaque pH after consumption of both fruit juices falls below the critical level for seven minutes and this decline is similar for both fruit juices.

Employing Resistive Superconducting Fault Current Limiters (RSFCL) is one of the practical and effective methods to improve the transient stability of a power system by limiting the fault current. Regarding technical and economical constraints, optimal sizing and allocation of RSFCLs in a power system is of significant importance. It is the purpose of this paper to propose an algorithm based on the Particle Swarm Optimization (PSO) in order to improve the transient stability of a power system by optimal sizing and allocation of RSFCLs. The proposed algorithm is next applied to the New England 39-bus test system as a case study and the results are simulated in Matlab. Simulation results reveal that in the case of employing RSFCLs with sizes and locations resulted from the optimization algorithm, the transient stability of the power system under study is improved. Furthermore, it seems that the optimal locations of RSFCLs are to some extent near the fault location.

BACKGROUND:One of the most important concerns about systemic lupus erythematosus (SLE) is the presence of oral lesions, which in turn is one of the diagnostic criteria for SLE. Regarding the wide range of oral lesions and the absence of comprehensive data in Iran, this study aimed to evaluate the prevalence of oral mucosal lesions and related factors in patients with SLE at three rheumatology clinics in Tehran.METHODS:This descriptive study was performed on 188 patients by observation, clinical examination, completing questionnaire and also evaluating patients' medical records. The lesions explored were ulcer, erythema, erythematous center with white striae or spots, and white plaques. Related factors taken into consideration were age, sex, smoking, frequency of pregnancy, oral health status, duration of disease, medications taken daily dosage of corticosteroid drugs, and the state of disease control. Sampling was done by the continuous method and data obtained were analyzed by SPSS version 16.0 and ordinal regression tests.FINDINGS:Out of 188 patients, 102 (54.3%) patients had oral mucosal lesions. The most prevalent lesion was ulcer (28.1%) and the most common region involved was the buccal and labial mucosa.CONCLUSION:With regard to the high prevalence of oral mucosal lesions in patients with SLE, it is of paramount importance to emphasize early detection of these lesions as a mean of diagnosis of disease and faster initiation of treatment.

In this paper, a black box model is proposed to ana lyze the transient state of distribution transformers. This model is capable of showing the frequency characteristics of the transformer under various conditions of the termina ls connections up to the frequency domain of almost 1.2 MHz. In addition, this model has satisfa ctory abilities in illustrating the characteristic of the wave transferred to the consumer side and it can be employed in studying the over voltages produced in the transformers terminals as the resul t of striking the lightning waves. In order to investigate the validity as well as the accuracy of the proposed model, a 6300/420 V, 2500 KVA distribution transformer is selected for the resear ch. First, required experiments are performed on this transformer and then, using the measurements r esults and applying the modal analysis, the model parameters are obtained. Comparing the result s of the model and the measurements findings shows that the proposed model can be utili zed for transient studies in distribution networks. Copyright © 2011 Praise Worthy Prize S.r.l. All r ights reserve.

It is the purpose of this paper to investigate the design of a stabilizer via sampling the speed and voltage feedback in order to improve the oscillations of generators in Siahbisheh pumped-storage power plant in Iran. An overall PSS is utilized for all of the generators and its output is connected separately to the generators excitation systems. Moreover, a terminal voltage feedback is employed for damping oscillations. Comparing the simulation results shows a considerable improvement in the oscillations of the rotor speed, generator power, and terminal voltage. The proposed method is feasible and cost effective.

In this paper a method based on the Particle Swarm Optimization (PSO) algorithm is presented for tuning Power System Stabilizer (PSS) parameters. In the proposed method, based on the optimization of a suitable objective function, optimal values for PSS controlling parameters including lead-lag compensator time constants as well as the controller gain are calculated. The employed objective function is the damping ratio of eigenvalues corresponding to system critical modes obtained from the analysis of the linearized model of system around the operating point. Controllable and critical modes of the system are identified using modal controllability and observability criteria. The proposed algorithm is applied to a single machine power system and for various operating conditions. Simulation results prove the capability of the proposed algorithm in damping improvement of power system.

If a disturbance occurs in a power system and then it is cleared, the machines in that system will initially oscillate, and then, when the transient energy becomes zero, they will settle at stable operation point. In this paper, the rate of reduction in transient energy is considered as an index of system damping. This concept is then used to find the additional damping provided by Static Synchronous Compensators (STATCOM) and Static Synchronous Series Compensators (SSSC). Analytical expressions for the index of system damping, provided by these devices, are derived and compared for the classical model of single machine connected to infinite bus (SMIB). The proposed technique, which is based on the rate of dissipation of transient energy, is then tested on the SMIB and the 6-machine SISTAN system. SISTAN system is a part of Iran national grid. The results derived from this new index verify the capability of these devices in damping power system oscillations.

In order to utilize a Static Synchronous Series Compensator (SSSC) in the steady state condition, it is to be controlled by several modes. The most important control modes of the SSSC are constant voltage mode, constant impedance mode, and constant power control mode. Besides, this device may be furnished with supplementary controllers, such as damping controls, to enhance the dynamic performance of system. In this paper, the influence of various SSSC control modes on small signal and transient stability of a part of the Iran national grid is investigated. Next, the performance of power oscillation damping (POD) is evaluated for different input signals. The simulation results demonstrate that the utilization of the SSSC in the constant impedance mode improves both the small signal and transient stability better than other control modes.

A great amount of the energy generated by renewable energy-based generation units, e.g. wind farms, is often rejected because of network restrictions. Moreover, most of renewable energy sources, such as wind and solar, are uncertain and uncontrollable. In order to overcome these drawbacks, the rejected energy can be applied to pumped storage power plants and reutilized via hydro-turbines when needed. Optimal sizing of such power plants is crucial in enhancing the recovery of the rejected energy. In this paper, optimal sizing of pumped storage power plants for increasing the penetration of renewable energies are studied. Both technical and economical aspects are considered. The analysed methods include evaluating the operation and optimal sizing of such systems through assessing the attainability of various objectives using single or multi-objective optimizations, parametric studies, and sensitivity tests. The results of this paper demonstrate the leading role of a well-optimized design for technical and economic viability of such systems.