Al-Rafidain Engineering Journal (AREJ)

Power quality problems in electric systems are one of the important topics that occupy a wide area of ​​interest to researchers and engineers. The increased use of power electronics circuits has led to improve efficiency and performance of the equipment; on the other hand, they withdraw a non-sinusoidal current and increase the harmonics which causes a decrease in the power quality. Also, these electronic devices are sensitive to power quality problems. However, advanced electronics can be employed to mitigate these problems. The Distribution static synchronous compensator (D-STATCOM) is one of the Custom Power Devices (CPDs) used for this purpose. D-STATCOM can be designed with different topologies, algorithms, and techniques of control to mitigate various power quality problems that face the power system. Selecting the D-STATCOM design depends on the power quality problem that needs to be mitigated. This paper presents a literature review of D-STATCOM from its beginnings to the present day.

Most of the loads in the distribution system are inductive loads, due to the nature of household loads, most of which are reactive power consuming motors. These loads have a low power factor and cause voltage drop and increased power losses in the wires. The system most affected by power loss and voltage drop is the low-voltage distribution system of 0.4 kV, due to the large current that passes in this system.
In this research, a simulation of a standard low-voltage radial distribution system (IEEE 30 Bus System) was carried out in the Power World Simulator Program in order to evaluate and improve the efficiency of the distribution system by manually installing capacitors at each consumer to correct the power factor to reduce voltage drop and electrical power losses in wires. The system simulation was conducted at constant loads, and the ineffective power was compensated for by its equivalent manually, by adding capacitors to keep the power factor close to Unity.
The research aims to study the effect of power factor correction for each consumer on the overall distribution system efficiency, to be a basis for designing an automatic power factor correction unit that can be installed in homes, commercial buildings, and small factories. The simulation results were promising in terms of improving the overall system efficiency and reliability.

Rising electricity consumption, rapid depletion of fossil fuels, and the global shift to the use of renewable energy resources have increased the need to integrate renewable and distributed energy resources (DERs), such as solar photovoltaic (PV) to power distribution networks. In this paper, the effect of photovoltaic system inverter scalability on reactive power compensation/absorption in a modified IEEE 13-node distribution network is studied. Power flow analyzes were conducted in MATLAB / SIMULINK software for different operating conditions to show the effect of reactive power on network voltage regulation, total harmonic distortion (THD) reduction, and power factor conservation in order to improve the system's power handling capacity. The result shows that the use of the PV system (500 kW) in Bus (671) led to a decrease in the generated power of the generator by 13.79%, the use of reactive power injection from the inverter of the photovoltaic system on site improved the voltage profile significantly. Also, the voltage distortion (THD-V) was reduced by 34% when injected with reactive power, and the current distortion (THD-I) was reduced by 57.65% when the reactive power was absorbed, and the power factor was improved on site.

Voltage stability of power systems reflects challenges to the power system operators due to its effect on the power systems components performances. Therefore, many solutions were invented in order to keep the systems within the voltage stability accepted limits. Because of the huge expansion of the power grids and the different loads natures on the grids, many techniques and solutions are used. The On Load Tap Changing Transformer (OLTC) was one of those techniques. In this paper, a review of past works that deal with the voltage stability limits, voltage stability improvement ways, OLTC types, the OLTC reverse action, and OLTC effect on voltage stability, in addition to several ways that make the OLTC work better. are discussed. The paper also sheds the light on the possible ways that may be employed to prevent the OLTC reverse action.  

Distance protection is considered important and essential in power systems. Due to the development of distribution systems and the system's topology change from time to time, integrating electric vehicles into the distribution system leads to an increase in short circuit level and injection of harmonics into the system. Since the vehicles are continuously variable loads, this leads to difficulty in adjusting the protections that depend on the current in the process of adjusting them. As a result, distance protection is used in distribution systems. This paper shows the effect of integrating electric vehicle charging stations on the relay performance of distance protection in the distribution system. Distance protection relay was built based on artificial neural networks adapted to the system conditions. The accuracy of the neural network model used for fault detection was (99.9%), and the error rate in locating the fault was (0.00079%).

The effect of the various winding connections of three phase two windings transformer on the fault current at the line to ground (SLG-fault) and the double line to ground (DLG-fault) is studied. The ground faults are unbalanced  ; so, the analysis of these types of short circuit faults is divided into three balanced circuits which are known as symmetrical  networks. The zero sequence impedance appears in some types of transformer connections and its effect is reflected in the fault current value. This paper examines with help of MATLAB software by simulating a generating station and different transformer connections, the impact of three-phase two windings transformer connections   which occurs on a transformer secondary side to determine which the connections type of the transformer   gives the maximum and minimum zero sequence component of ground fault current.

In recent times,   Multilevel inverters are considered an essential component of power electronics with widespread use in a wide range of high-voltage and high-power industrial and commercial applications.  The use of multi-level inverters, also known as MLIs, has been preferred over conventional inverters due to the characteristics that these MLIs possess. These characteristics include low harmonic distortion caused by satisfacory performance of MLIs.  This paper is concerned with analyzing harmonics to gain a deeper understanding of the performance of cascaded H-Bridge multilevel inverters (CHB-MLI). The model was constructed by using MATLAB/SIMULINK. A comparison was made between an asymmetrical cascaded 27 and 31-level multi-level inverter (MLI) by using the Phase disposition sinusoidal Pulse Width Modulation (PD-SPWM)and Phase Opposition Disposition sinusoidal Pulse Width Modulation  (POD-SPWM) techniques. According to the outcomes of the simulations, 31 levels are better than 27 where Total Harmonic Distortion ( THD) in 31 levels is lower than 27 levels. The best result obtained during this study is  31 levels that use (PD-SPWM) technology, where the percentage of total harmonic distortion is small compared to the rest of the results and equal to 3.63%.

Electrical power systems operate at 50 Hz. However, generation loss, a sudden increase in loads, or faults in the system cause disturbances and deviations that destabilize the frequency of electrical power systems. Therefore, there is a need to study and improve the frequency stability of electrical power systems during disturbances. The present study examines improving the frequency stability of electrical power system, using a solar photovoltaic (PV) system, a battery energy storage system (BESS), and underfrequency load-shedding (UFLS) to estimate and control the frequency.The proposed method was tested on a standard Institute of Electrical and Electronics Engineers' (IEEE®) 9-bus system that was simulated in MATLAB® Simulink. The simulation results indicate that the used method significantly stabilizes the frequency of electrical power system.

This work was devoted to the development of a simulation model of the grounding and lightning protection system for oil tanks, taking into account the frequency dependence of soil parameters, where we, based on the equations mentioned in previous studies, designed a grounding model for an oil tank taking into account the frequency dependence of soil parameters by using the finite elements method. and for different configurations, where it was observed that the grounding potential rise GPR was significantly reduced at high frequencies, especially in the case of high soil resistivity, the percentage of decrease in the grounding potential rise in the case of dry soil for the studied site 1266.65 Ω.m and for wet soil 596.27 Ω.m, respectively, 22.8%  and 23.8%, respectively. and it was pointed out the necessity of conducting soil resistivity measurements before the tank construction process, and the need to use the network configuration of the oil tank grounding model in some cases where the soil resistivity is high and it is difficult to eliminate the effect of lightning current with the typical design mentioned in NFPA 780 for tank grounding.

The power quality (PQ) is a major issue for both electrical utilities and their customers. The nonlinear loads cause PQ problems like current harmonics, voltage harmonics, frequency deviation, voltage sag and voltage swell. A unified power quality conditioner (UPQC) is utilized in this research to minimize these PQ problems. The UPQC is made up of two active power filters (APFs), one of which is connected to the line in series and the other in parallel. The Unit Vector Template Generation (UVTG) approach is used to control the series APF, whereas the Synchronous Reference Frame (SRF) technique is used to control the shunt APF. The compensating properties of a series-shunt APFs when the loads become imbalanced have been explored. The system performance has been tested under conditions current harmonics, voltage harmonics, voltage sag, and voltage swell. The voltage harmonics are identified and reparation in a series APF using the UVTG technique, whereas the harmonics and unbalanced currents are identified and reparation in a shunt APF using the SRF method. An IEEE-519-compliant THD (Total Harmonic Distortion) of less than 5% is achieved by UPQC in simulations with unbalanced loads. The findings indicate that harmonic currents and supply voltage fluctuations were lessened by UPQC.

When connecting two generators together (in parallel), there are conditions that must be met and fulfilled before commencing the electrical connection process, which are known as synchronization conditions. In this paper, the loss of equality voltages which is one of the synchronization conditions will be represented when performing the connection process using Matlab and surveying the impact of this on the performance of the system and the extent of damage that may result from it. The presented analysis shows the influence of faulty synchronization on the following physical quantities: internal voltage, stator current, stator voltage, angular mechanical speed, terminal voltages which are the most vulnerable. In addition, knowing the type of fault (short circuit fault) caused by the faulty synchronization condition. In this paper, over and under voltage schemes have been implemented by using MATLAB/SIMULINK.

Power generation is normally produced at constant frequencies of 50 Hz or 60 Hz and the generators E.M.F can be considered practically sinusoidal. However, when a source of sinusoidal voltage is applied to a nonlinear device or load, the resulting current is not perfectly sinusoidal. Due to non-linear loads, distortions are produced in the sinusoidal waveform so filters are used to minimize these distortions. This paper aims to build a simulation model of a nine-bus ring system to evaluate characteristics of harmonics in different cases of study using electrical transient and analysis program (ETAP), which is considered one of the best tools to study harmonics in the power system, thus, the harmonic distortion is analyzed in ETAP. To generate harmonic distortion in the power network, a general load is modeled as a source of harmonics. A harmonic load flow analysis was carried out in order to determine the impact of harmonic current on a power network, and the THD% of all types of harmonic models on all the buses was checked and the typical IEEE model that has the highest THD% was chosen and compared with the model that contains low THD indices (one of the best models of IEEE manufacturer).

Electrical power systems around the world are currently operating near the limits of security and stability design, due to economic considerations and high rates of demand for electrical energy. During their operation, these systems are exposed to various types of disturbances, which in severe cases lead to their complete loss and complete shutdown. Dynamic security assessment is one of the most important tools used in evaluating the performance of electrical power systems after these disturbances occur. The traditional mathematical methods for evaluating dynamic security require complex computations and computational time so that they are not suitable for evaluating dynamic security in real time. To address these challenges, this research was conducted to provide new tools based on advanced techniques of artificial intelligence techniques capable of building a classifier to evaluate its dynamic behavior in real time. The research methodology in this study relied on the use of artificial intelligence techniques, including back propagation artificial neural network, decision tree algorithms (J48) and logistic model tree (LMT). Which was applied to the emergency database of the electrical power system (IEEE 14 Bus) test model after applying the most common types of electrical disturbances. The results of the artificial neural network technology showed high classification accuracy (98.958%) and a lower error rate compared to the decision tree (J48) and (LMT) algorithms. The results of this research are very important to improve the accuracy of the results of the dynamic security assessment classifier for the electrical power system, which makes it easier for the network operator to take appropriate protective measures in the moment of disturbances in the network.

The Iraqi electrical system suffers from an increased electrical load for the available generation, which leads to the separation of a large number of consumers, especially during the peak load period. The water heating load represents a great value, so reducing water heating consumption can reduce the cut-off times. Solar water heaters possess many benefits. Therefore, they are used in many countries in the world today. The climate of Iraq is mostly hot and sunny. This makes using a solar water heater is convenient for consumers, especially in urban areas. For studying the use of solar water heaters in the residential sector, three consumers were selected in Mosul city in northern Iraq. Each consumer differs from the others by the value of their consumption of electrical energy (high, medium, and low). Electricity tariffs for the residential sector in Iraq vary, depending on consumption.  The information for the three consumers was obtained from a previous questionnaire. In addition to obtaining their needs for hot water, the results of using solar water heaters on the roofs of the three houses of consumers showed a decrease in electricity consumption and a noticeable saving in the electricity bill. The payback period of the solar water heater system was calculated for each consumer.  Reducing consumption reduces the gap between generation and load, resulting in reduced programmed shedding times for consumers. For these benefits and environmental features, it is necessary to generalize the use of solar water heaters in the residential sector in Iraq.

The spread of distributed power stations, especially small power stations that use renewable energy sources, as well as the connection of a large number of distributed power stations to the network led to the necessity of making some changes in the electrical distribution system. Therefore, the Solid State Transformer (SST) has recently emerged as a suitable alternative to the traditional transformer. SST is characterized by its small size and weight, and   as the possibility of controlling the direction and amount of power flow, improving the quality of power, the possibility of controlling voltage, compensating reactive power and other advantages that are not available in the traditional transformer that can be of paramount importance to the development of the power system. This paper reviews solid state transformers in terms of their components, working method, mathematical analysis, design steps, and control process. ANSYS Maxwell 3D software was used to design and model the high frequency isolation transformer and a working model of the core-type high frequency isolation transformer was presented. It was found through the results of the study and analysis of the solid-state transformer that it would be a suitable alternative to the traditional transformer that works at high frequencies.

One of the problems that face the use of XLPE insulators is the appearance of defects. These defects appear during the manufacturing processes of the insulator, and one of these defects is air cavities or voids. The defects presence within the insulators of high voltage cables affects the distribution of the electric field within the cable layers. The distortion of the electric field due to the presence of air cavities is the main reason for the treeing appearance inside the insulator, which eventually leads to the emergence of partial discharges that reduce the life of the cable. In this study, the effect of the presence of an air cavity inside an XLPE insulator was studied by changing the dimensions of the cavity, that is, changing the ratio of the dimensions of the cavity parallel to the electric field and vertical to it and the effect of this on the value of the electric field in the center of the cavity. It was noted that the electric field in the cavity is higher than in the external electric field. The increase in the field in the cavity center does not depend on the cavity size, but rather on the ratio of the cavity dimensions parallel to the electric field to the vertical to it. The electric field enhancement factor was calculated based on the simulation results, which showed a reasonable agreement with the theoretical values.

Because of the fast advancement in the creation of power electronics equipment such as automatic Machines, adjustable speed drives, personal computers and other non-linear loads which are the main sources of harmonics. Due to the presence of these nonlinear loads, it is necessary to reduce the level of harmonics created in the power networks. Hence, harmonic analysis of distribution networks is important. The analysis of power systems is an important part of power system engineering. Any electrical utility company's principal goal is to provide the best quality of power. The power system harmonics is one of the major reasons of poor power quality. Harmonics and harmonic analysis must be investigated in filters in order to minimize harmonic current and voltage. This paper aims to build a simulation model of nine bus ring system to evaluate characteristics of harmonics in different cases of study using Electrical Transient and Analysis Program (ETAP). Using ETAP harmonic distortion is analyzed and mitigation techniques are used represented bysingle tuned filters which should be installed for worst case and the best-case condition. And the simulation results of ETAP shows that some of THDv,i%  results are within the limit value as per IEEE 519 -1992 standard.

In this research, a study was conducted to re-evaluate the safety levels of the grounding system for the Mosul Secondary University distribution station, by taking the effect of the conductors of the foundation arming grid on the electrical potential distribution resulting from faults to the grounding system implemented by the Lebanese company (MATELEC s.a.l). A fault current of (20kA) was adopted. The CYMGRD program was used to re-design the grounding system implemented by the company in two stages, first without taking the effect of the arming grid of the foundations, and then the grounding system was redesigned by adding the arming grid of the foundations implemented inside the concrete and linking it with the basic grounding system that was formed of conductors and grounding rods, and the results showed the significant effect of the foundation arming grid in reducing the levels of touch voltage (Em) by 33%.

A virtual power plant (VPP) is considered a combination of distributed generation connected with energy storage devices and interruptible loads. This system is controlled as a single flexible unit in the electricity market and in the main grid. Due to numerous problems in the main grid such as variation of frequency and the Interruption in power supply as a result of the peak load. As well as economic and material constraints, Considered the optimization solution for scheduling resources and overcome for these problems is VPP. This study proposed different scenarios for two-sector of homes in Iraq which simulated in Matlab Simulink software. The method is implemented on a test system with a VPP comprising a distribution generator, energy storage devices, and loads. The economic characteristics of these resources and of the network were calculated. the results showed a decrease in the bill of electricity for these homes by 50%. Simulation results display a benefit from the use of VPP when compared to DG based only on renewable interrupted generation.

The electrical load is affected by the weather conditions in many countries as well as in Iraq. The weather-sensitive electrical load is, usually, divided into two components, a weather-sensitive component and a weather-insensitive component (baseload). The impact of the weather-sensitive component includes the summer and winter periods, without distinguishing between them. The characteristics and specifications of this component differ in summer and winter due to the different loads in the seasons, so it is best to separate these two components into two independent components. The research provides a method for separating the weather-sensitive electrical load into three components, the summer component, the winter component, and the base component. The artificial neural network was used to predict the weather-sensitive electrical load using the MATLAB R17a software. Weather data and loads were used for one year for Mosul City. The performance of the artificial neural network was evaluated using the squared error rate and the mean absolute error ratio. The results indicate the accuracy of the prediction model used in the research.

Stability of power system is the ability of the system, with a certain initial operation conditions, to restore the operating balance conditions after exposure to disturbance such as faults or sudden load changes. More attention is required to address voltage instability problems to keep voltage profile under control during abnormal conditions. This paper proposes a Static Synchronous Compensator (STATCOM) using (MATLAB / Simulink Program) The STATCOM includes proportional-integral (PI) control model is used to control the voltage during abnormal conditions by absorbing or injecting reactive power into the power system. Simple and reliable PI controller has been used and designed to be stable under various operating conditions. Three phase Two level PWM strategy technic used in STATCOM controller to decrease the harmonics injected after adding STATCOM to the power system (THD = 2.21%). The simulation study has been done by using 9 buses IEEE system after making a disturbance such as sudden load change. Then the voltage profile during this interval is being studied with and without using STATCOM. The simulation results show that adding STATCOM to this system led to improve the voltage profile during disturbance interval and made the system more stable and reliable by preventing the disturbance effects from reaching the generation side (Vbus 5 = 0.8980 pu, during disturbance before adding STATCOM, Vbus 5 = 1.0003 pu, during disturbance after adding STATCOM). The fast response of the STATCOM controller gives the ability of injecting or absorbing reactive power during disturbances and keeping the system voltages within the IEEE standards limits (0.95 pu > V> 1.05 pu).

The electrical energy crisis is a global problem that all developing countries face in general and Iraq in particular. A lot of body in the literature holds that lifestyle and consumption choices strongly affect residential energy consumption. Hitherto releasing energy savings in households is not simple. Previous studies indicate that the lighting requirements for the residential sector consume a significant amount of Iraq’s energy resources. In this study, the authors analyzed the energy consumption of 48 samples of residential loads at different dwellings in the country. In addition, the simulation study based on the DIALUX Evo 8 lighting software has been conducted, which shows the energy consumption savings for various types of luminaires. The results clearly show that a relatively large portion of lighting system consumption is because of the poor distribution of lighting fixtures and the use of relatively high-consuming traditional lighting luminaires. The study deduces that the energy efficiency of the lighting system may be improved by about 60% by simply replacing the traditional lighting systems with modern LED-technology-based systems. It is also necessary to redistribute lighting fixtures using state-of-the-art lighting software for achieving adequate levels of lighting and visual comfort for humans.

In this article,  H∞ /μ controller is relied on to control the power system stabilizer(PSS) using state space approach for a single machine infinite bus (SMIB) system. Design a robust feedback controller for the system using the H∞/μ technology supported by the Matlab / Simulink. The H∞/μ design method leads to a robust controller with a fixed structure and fixed parameters. The uncertainties of the model are taken into account when specifying the weights. The controller demeanor obtained was analyzed through the input represented by the step response and the output response of the power system (PS) in the case of normal operation and then the system with changed parameters. The suggested controller proved its effectiveness by maintaining the stability of the system with acceptable limits of disturbances.

The Flexible Alternating Current Transmission systems(FACTs) devices is power electronics constructed system used to increase the capability of the transmission line. It has several types with different functions for example: SVC, STATCOM,DSTATCOM, TCSC, SSSC, IPFC and UPFC. The Static Synchronous Series Compensator (SSSC) used to control the active power of the transmission line by injecting controllable ac voltage in the series with the transmission line. The Static Synchronous Compensator (STATCOM) employed to control the reactive power by injecting adjustable ac current in the transmission line. The Unified Power Flow Controller (UPFC) consists of SSSC and STATCOM linked by DC capacitor, it controls both active and reactive power flow of the line. This paper presents a simulation study to compare between SSSC, STATCOM and UPFC by inserting each device separately on a 100 MVA, 500 KV, four busses power system. Each converter is designed by 48-pulse multilevel inverter to reduce harmonics contents of the line voltage. This study has been done using MATLAB / SIMULINK package.

This paper introduces different topics about six phase induction motor drives. It describes a different methods used for analyzing and representing induction motor model, by using (d-q-o) modelling and (x-y-o) some papers discussed motor model and its characteristics, controlling speed of motor and efficiency improvement. some techniques of control strategy such as (direct torque control, field oriented control, indirect field oriented control and sliding mode control etc. will be present to improve motor operation.as well this paper will present some techniques for voltage generation used to drive motors, some methods are implemented for this purpose depending upon quasi voltage generation, pulse width modulation, and space vector pulse width modulations etc are also discussed.