Ahmed M. Azmy

Improving Fault Ride-Through Capability of DFIG-Based Wind Turbine Using Superconducting Fault Current Limiter

With increased penetration of wind energy as a renewable energy source, there is a need to keep wind turbines connected to the grid during different disturbances such as grid faults. In this paper, the use of superconducting fault current limiter (SFCL) is proposed to reduce fault current level at the stator side and improve the fault ride-through (FRT) capability of the system. To highlight the proposed technique, a doubly fed induction generator (DFIG) is considered as a wind-turbine generator, where the whole system is simulated using PSCAD/EMTDC software. Detailed simulation results are obtained with and without SFCL considering stator and rotor currents. In addition, the voltage profile at the generator terminals is analyzed. The effect of limiting resistance value is also investigated. The obtained results ensure that the SFCL is effective in decreasing the fault current. Moreover, both the voltage dip at the generator terminals and the reactive power consumption from the grid are decreased during the fault. The voltage dip characteristics are discussed in accordance with international grid codes for wind turbines.

Dispersion behavior and breakdown strength of transformer oil filled with TiO 2 nanoparticles

Recently, the study of transformer oil-based nanofluids became of great interest, due to their prospective properties as a dielectric and cooling medium. However, agglomeration of nanoparticles limits the beneficial properties that can be obtained from nanofluids. So, the work presented in this paper aims to get enhanced dispersion behavior of nanoparticles within transformer oil-based nanofluids. Then, breakdown strength with the enhanced dispersion behavior is evaluated. In order to get enhanced dispersion behavior, nanofluids were prepared using nanoparticles with a surfactant. The surfactant plays a role in the stabilization of nanoparticles and maintaining suspension stability. The considered type of nanoparticles is TiO2 nanoparticles. Two series of nanofluid samples were prepared. Through the first series, the effect of surfactant concentration on dispersion behavior and agglomerate size was studied. The dispersion of nanoparticles was characterized using three different techniques. These techniques are optical microscope analysis, transmission electron microscope (TEM) analysis and zeta potential measurements. Based on these techniques, the suitable concentration of surfactant was identified. The second series of nanofluid samples was prepared with different weight percents of nanoparticles for assessing the breakdown strength. Weibull distribution was used to calculate the breakdown probability for the base oil as well as nanofluid samples. The results showed an enhancement in the breakdown strength by about 27% in comparison to the base oil. Based on the obtained results, mechanisms behind the dispersion behavior and breakdown strength were proposed and discussed.

Effect of titania nanoparticles on the dielectric properties of transformer oil-based nanofluids

In this paper, a study on the dielectric properties of transformer oil-based nanofluids is presented. Titanium oxide nano ceramic particles, known as titania nanofillers, was used in the investigation process. The nanofluid samples were prepared using two-step method, in which, nanoparticles were mixed with the base oil and then dispersed using magnetic stirrer, dispersants and ultrasonic processor. Different amounts of dispersants were considered and the best amount of dispersant was determined according to the observed images obtained by an optical microscope. Different nanoparticle volume fractions were considered, starting from 0.1 g/L to 0.3 g/L. Breakdown strength was measured for the prepared samples using a liquid tester and then compared to that of the base oil. The breakdown strength increased significantly with the addition of nanofillers. The obtained results will enable to develop a new class of liquid dielectrics with a visibility for the application into power transformers.

Optimal Power Flow to Manage Voltage Profiles in Interconnected Networks Using Expert Systems

The optimal power flow issue is one of the most important problems faced by dispatching engineers regarding large scale power systems. It is a particular mathematical approach of the global power system optimization problem that aims at determining the least control movements to keep power system at the most desired state. Thus, it represents a flexible and powerful tool, which can address a wide range of planning and operation studies. However, the complexity of optimal power flow increases dramatically with large-scale networks, which often discourages the utilization of this powerful tool in many applications. This paper proposes a new intelligent approach to facilitate the implementation of the optimal power flow calculations to be utilized in various control centres. A main advantage of the proposed intelligent systems with real control centres is the possibility of controlling the system voltage profile in a tracking mode. The simulation results using this intelligent system when applied to the IEEE 30-bus power network emphasize the validity and effectiveness of the proposed technique.

Protection Coordination for Distribution Systems in Presence of Distributed Generators

Abstract Coordination among protective devices in distribution systems is affected by inserting distributed generators. This is attributed to the changes in power flow in addition to the changes of magnitudes and directions of fault currents, which cause mis-coordination between protection devices. This article presents a new protection coordination to overcome the impacts of distributed generator units and to avoid the mis-coordination problem. The proposed protection coordination depends on activating the directional protection feature, which is available in most modern microprocessor-based reclosers. This will be accompanied by updating relays and recloser settings to achieve the correct coordination without extra costs or equipment in the distribution system when equipped with an autorecloser. A real 11-kV feeder, simulated by the ETAP package (ETAP, Irvine, California, USA), is used to prove the effectiveness of the proposed protection coordination. The results ensure the possibility of achieving proper coordination between protective devices after inserting distributed generator units if suitable settings of these devices are realized.

Impedance-based fault location technique for distribution systems in presence of distributed generation

This paper presents an analytical technique for fault location in distribution systems in presence of distributed generation (DG). The presence of DG changes the nature of power flow from unidirectional to multidirectional. Therefore, the accuracy of impedance-based fault location methods will be affected by the presence of DG. The proposed technique is a modification of impedance-based methods to be suitable for systems containing DG based on voltage and current measurements at the power substation. To evaluate this technique, it is implemented on an 11 kV feeder using ATP/EMTP package. The results achieved ensure the validity and accuracy of the technique.

Adaptive differential evolution algorithm for efficient reactive power management

Display Omitted An adaptive differential evolution procedure is presented to solve optimal reactive power dispatch problem.A multi-objective function aims at minimizing power losses and enhancing voltage profile.An investigated strategy for adaptive penalty factor to alleviate the effects of dependent variable violation.Numerical applications are carried out on three standard IEEE test systems and on a Western Delta real system.The flexibility of synchronous machines as reactive power sources is proven compared to switchable devices. This paper introduces a proposed procedure to solve the optimal reactive power management (ORPM) problem based on a multi-objective function using a modified differential evolution algorithm (MDEA). The proposed MDEA is investigated in order to enhance the voltage profile as well as to reduce the active power losses by solving the ORPM problem. The ORPM objective function aims to minimize transmission power losses and voltage deviation considering the system constraints. The MDEA aims to enhance the convergence characteristic of the differential evolution algorithm through updating the self-adaptive scaling factor, which can exchange information dynamically every generation. The scaling factor dynamically adopts the global and local searches to efficiently eliminate trapping in local optima. In addition, a strategy is developed to update the penalty factor for alleviating the effects of various system constraints. Numerical applications of different case studies are carried out on three standard IEEE systems, i.e., 14-bus, 30-bus and 57-bus test systems. Also, the proposed procedure is applied on Western Delta Network, which is a real part of the Egyptian main grid system. The flexibility of synchronous machines to provide controllable reactive power is proven with less dependency on the discrete reactive power controllers, such as installing the switchable devices and variations of tap changers. The obtained results show the effectiveness of the proposed enhanced optimization algorithm as an advanced optimization technique that was successively implemented with good performance characteristics.

Dielectric properties of aged mineral oil filled with TiO2 nanoparticles

When mineral oil is exposed to aging processes during their operation, oil properties significantly deteriorate. This necessitates reclamation of the oil or replacement with a new one. Both solutions are not preferred due to their high cost. From this viewpoint, this study aims to enhance aged oil properties by using nanofillers to be suitable for reusing in power transformers. Accelerated aging test is carried out through heating oil at 120 °C in an oven for different periods of days. Under this condition, accelerated aging for one day is considered to be equivalent to aging for one year in the field. Nanofluids are prepared by direct mixing of nanoparticles with degraded mineral oil. The considered nanoparticles in this study are titanium oxide nanoparticles. The breakdown voltage for prepared nanofluids are measured and compared to that of pure aged oil. Also, dielectric constant and dielectric dissipation factor have been measured. Nanofluids exhibited significant enhancement either in breakdown voltage or in dielectric dissipation factor. The physical mechanisms behind the obtained enhancement have been discussed considering the effect of aging and the role of nanofiller. It is found that nanoparticles alleviate the effect of moisture through adsorbing moisture species and forming hydroxyl groups around the surface of nanoparticles.

Assessing the effect of design parameters on optimal size of isolated PV systems for residential utilizations

This paper investigates the effect of varying different operating and design parameters on the sizing and economics of standalone PV systems for residential utilization. Each subsystem is sized using simplified mathematical expressions considering the effecting parameters as input variables. Thus, the sizing and economics of the entire system can be investigated in a generic form. The cost of each system component is analyzed based on international prices and aggregated to obtain the overall cost of energy (COE). The study is based on a 5 kWh/day residential load. A peak load power of 1300W is considered when sizing the inverter capacity. Among the design factors, the battery bank voltage, charge controller type, the solar irradiation and the depth of discharge (DOD) are investigated to examine their effect on the system economy. The analysis results show that the COE relies heavily on both the size and the selected design voltage of the battery bank, which in turn depend on the storage hours, charger size, the (DOD) value and solar irradiation.

Sizing and Economic Analysis of Standalone PEM Fuel Cell Systems for Residential Utilization

This study discusses the economic utilization of proton exchange membrane fuel cell (PEMFC) based on cost of energy (COE) to supply residential electrical and thermal loads. The fuel cell system is sized using simplified mathematical expressions considering the stack degradation and the system salvage value at the end of its life time. The study is based on a 5 kWh/day residential load with a peak load power of 1300 W. Two scenarios for economic survey are studied. The first scenario is to find the commercial price for each FC component considering that the supply fuel is hydrogen. The other scenario is for a complete FC system commercial price considering that the supply fuel is natural gas. The economic analyses are based on the actual sale prices in the market. The COE of the fuel cell system is compared with previous work by the authors for the same residential ratings but supplied from a stand-alone photo voltaic system (SAPV). The analysis results show that the COE relies heavily on the capital cost...