Mohamed Emad Farrag

Statistical Quantification of Voltage Violations in Distribution Networks Penetrated by Small Wind Turbines and Battery Electric Vehicles

Voltage violation tends to be one of the dominant constraints or critical factors that limit the penetration of small wind turbines (SWTs) and battery electric vehicles (BEVs) in distribution networks. To quantify the voltage violation, a statistical time series based approach is developed in this paper. The daily time varying characteristics of electric loads, wind speeds and BEV charging loads have been taken into consideration in a statistical manner. The method has been compared with the conventional time series approach. It is proven that the proposed methodology, while providing a global picture on voltage violations, can potentially be used for fast evaluation of the probability of a voltage violation occurring in a network. The methodology has been applied to an example distribution network. Results show that the proposed methodology can reduce the computational requirement by over 98%, while the difference between the results obtained using the proposed method and applying the conventional time series approach is within 12.5%.

Design of fuzzy based-rules control system for the unified power flow controller

The unified power flow controller (UPFC) is one of the flexible AC transmission systems (FACTS) devices that has the unique capability of independently controlling the real and reactive power flow at different transmission angles, in addition to regulating the system bus voltage. In this research, the mathematical analysis of the effects of the UPFCs VA rating and the system short circuit level (SCL) on the power flow are investigated to define the overall feasible operating area. Based on this analysis a new fuzzy logic controller has been proposed to improve the system performance. The controller rules are structured depending on the relationship between the series/shunt inserted voltages and the desired changes in real/reactive power flow in the power system. A power flow optimiser is designed based on real power priority logic and the on-line estimation of the SCL to define the appropriate operating point under different system contingencies. Three case studies are conducted to verify the capability of the UPFC and the effectiveness of the proposed fuzzy controller at different operating conditions.

Investigating the Impacts of Distributed Generation on an Electrical Distribution System Already Stressed by Non-Linear Domestic Loads

Distributed generation is becoming an integral part of electrical distribution systems, which implies a subsequent increase in the induction of power electronic inverters into the power systems. These inverters being non-linear in nature produce harmonic distortion in voltage. To worsen the scenario, the present day distribution systems are already frazzled by many non-linear domestic loads. The adverse effects of high level of harmonic distortion are well established in the theory. Therefore, it is of utmost importance to investigate the impacts of distributed generation on the harmonic distortion level of a residential distribution system already stressed by non-linear domestic appliances. This research work makes an effort to address the very same issue. The experimentally developed harmonic model of an inverter is deployed to perform the simulation of a typical UK distribution system in Electrical Transient Analyzer Program. The results show a remarkable increase in the total harmonic distortion in the voltage and third individual harmonic in voltage, in the presence of distributed generation, at the point of common coupling. However, the total harmonic distortion in the current reduces which subsequently reduces the line losses.

Review of Energy Storage Systems in electric grid and their potential in distribution networks

Concerns over changes to the global environment and the growing need for energy have increased the penetration of renewable energy (RE) generation into low voltage distribution networks. The introduction of Energy Storage Systems (ESS) into distribution networks has been proposed to improve the reliability and performance of power systems. Energy storage systems will also be important in helping to regulate the supply from intermittent RE sources that feed into variable load demand. The focus of this paper is to provide an overview of the state of the art of ESS, concentrating on the distinct characteristics and applications of the different types. The analysis includes comparison and evaluation of different storage preferences with regard to integration of these technologies with an electric grid at the distribution network level that may lead to benefits such as distribution upgrade deferral and improvements in power quality and reliability.

Power transformer health monitoring: A shift from off-line to on-line detection

Transformers are an important part of the electrical power system network, therefore, its fault detection is vital. Off-line methods are commonly used for their fault detection. These methods have associated costs derived from the necessity of taking the transformer out of service. The application of on-line methods reduces the expected costs and the possibility of unpredicted failures. In the present study, off-line and on-line methods are applied to the detection of short circuits in transformers, demonstrating the possibility of moving from off-line to on-line methods. Short circuits between sections in a transformer winding, between winding and core and between windings have been considered. PSPICE software is used to simulate the transformer for both detection methods. A comparison of the fault indication in both techniques proves the possibility of moving from off-line to on-line method. Sweep Frequency Response Analysis (SFRA) is considered an accurate technique for off-line tests. The changes in the windings inductance and capacitance affect the number of poles in the system response, so the number of poles will indicate the number of healthy sections. For on-line method, measurement of primary/secondary voltage/current is used to determine the measurable values which would result from a range of internal short circuit faults. From the simulated results, it is found that primary current can be used as the main indicator for the primary winding short circuits; a combination of secondary voltage and primary current is found to be useful for detecting secondary winding faults. Secondary winding voltage can be the main indicator for the cross windings short circuits.

Investigation of on load tap changer control in smart distribution network

Penetration level, location and intermittent behaviour of the Distributed Generations (DGs) integrated with the distribution system will have great impacts on the system performance and stability. One of the subjects is high voltage rise at tail end of radial feeder. Electric utilities use On Load Tap Changer (OLTC) attached to Medium Voltage (MV) transformer to regulate voltage levels. Traditionally, in passive network tap changers receive control signals from single bus and change the tap positions to maintain voltages at pre-defined reference voltage. In the active smart distribution network, and with the advantages of smart meters, OLTC can pick up control signals from different voltage buses and change the tap positions of the transformers accordingly. In this research, typical UK Low Voltage (LV) network with DGs is modeled on Matlab/Simulink and OLTC is installed at both MV and LV transformers (T/F). Logical controller is designed to select the most appropriate control signals from the system buses to optimize the operation of both MV and LV transformer collaboratively. Recommendation of integrating Energy Storage Systems at distribution network is discussed in this research in order to level up the load profile and stabilize the system voltages.

Chaotic Adaptive Particle Swarm Optimisation using logistics and Gauss map for solving cubic cost economic dispatch problem

This paper proposes Chaotic Adaptive Particle Swarm Optimisation (CAPSO) algorithm to solve Cubic Cost Economic Dispatch (CCED) problem. A Chaotic Local Search operator (CLS) is introduced in the proposed algorithm to avoid premature convergence. The basic strategy of the proposed algorithm is combining PSO with Adaptive Inertia Weight Factor (AIWF) and CLS, in which PSO with AIWF is applied to perform global exploration and CLS is used to perform exploitation to find the optimal solution. Logistics and Gauss map technique is used in performing CLS and the results are compared. The applicability and high feasibility of the proposed method is validated on a standard 5-generator test system. The simulation results confirm that this algorithm is capable of giving higher quality solutions with fast convergence characteristics.

Particle swarm optimization with Exponentially Varying Inertia Weight Factor for solving Multi-Area Economic Dispatch problem

This paper aimed at exploring the performance of Particle Swarm Optimisation with Exponentially Varying Inertia Weight Factor (PSO-EVIWF) for solving Multi-Area Economic Dispatch (MAED) problem with tie line constraints considering valve-point loading in each area. The effectiveness of the proposed algorithm has been verified on 4 interconnected areas with 16 generators standard test system. The paper presents the search capability and convergence behavior of the proposed method. Simulation results show that the PSO-EVIWF achieved quality solutions and smooth convergence characteristics and it is an alternative method for solving MAED problem.

Enhanced condition monitoring of power transformers through improvement in accuracy of DGA interpretation

Transformer failure in electricity supply grids has a high financial impact, due to failure to meet commercial contract and possibility of transformer replacement cost. Therefore, detecting fault inception is very important in order to keep the transformer operating with recommended efficiency, hence ensuring stability of the electric network. Dissolved gas analysis (DGA) of a transformer can provide clear indication of thermal and electrical stresses on power transformer insulation and is considered as one of the most effective tools for oil-filled power transformer diagnostics. DGA is used to detect incipient faults in order to manage the fault severity. Both on-line and offline condition monitoring methods can be applied to obtain gas content, thereafter there are many interpretation techniques for DGA results. The accuracy of these techniques is dependent on the operators experience and knowledge of the materials and equipment involved. In this work, a combined fuzzy logic analysis technique for monitoring of power transformers based on DGA analysis is proposed, the system uses the 7 key gases to diagnose the health of the transformer and, where applicable, fault type. Initially, gas levels are considered using the IEEE standard as a basis to indicate the health of the transformer. A combined fuzzified analytical tool, based on Duval Triangle, Doernenburg ratio and Key gas method, are analysed to identify the fault type, improving on the accuracy of the individual interpretation techniques. The analytical tool has been applied to 444 sample faults reported in the literature to assess the accuracy of the proposed system. Results presented show the systems overall decision has improved capability of identifying the transformer condition over individual methods. The proposed system is proved to have 99 % accuracy in identifying the transformer normality. For cases where transformers were faulty, the approach has 98.76% accuracy in recognising the actual fault, superior to individual approaches.

Smart network benefits in developed / developing countries

Smart Network, is defined as “an automated, widely distributed energy delivery network characterized by a two-way flow of electricity and information, capable of monitoring and responding to changes in everything from power plants to customer preferences to individual appliances”. This tutorial is presenting an introduction to smart networks, including;