Mamdouh Abdel-Akher

Fault Analysis of Multiphase Distribution Systems Using Symmetrical Components

The paper presents a new approach for performing the fault analysis of multiphase distribution networks based on the symmetrical components. The multiphase distribution system is represented by an equivalent three-phase system; hence, the single-phase and two-phase line segments are represented in terms of their sequence values. The proposed technique allows the state of the art short-circuit analysis solvers to analyze unbalanced distribution networks. The fault currents calculated using the proposed technique is compared with the phase components short-circuit analysis solver. The obtained results for the IEEE radial test feeders show that the proposed technique is accurate. Based on the proposed method, the existing commercial grade short-circuit analysis solvers based on sequence networks can be utilized for performing unbalanced distribution systems.

Development of unbalanced three-phase distribution power flow analysis using sequence and phase components

This paper presents a new power-flow method for analyzing unbalanced distribution networks. In this method, an unbalanced distribution network Is decomposed to: 1) main three-phase network with three-phase line segments and 2) unbalanced laterals with two-phase and single-phase line segments. The proposed method allows solving the main three-phase network based on the decoupled positive-, negative, and zero-sequence networks. The unbalanced laterals are solved using the forward/backward method In phase components. The solution process Involves three main steps. Firstly, In phase components, the backward step Is executed to calculate an equivalent current Injection for each unbalanced lateral. Secondly, the main three-phase network Is solved In sequence components. The standard Newton-Raphson and fast decoupled methods are used for solving the positive-sequence network whereas the negative- and zero-sequence networks are represented by two nodal voltage equations. Finally, In phase components, the forward step Is performed to update the voltages In the unbalanced laterals. The three-steps are repeated till convergence happen. Distribution network characteristics such as line coupling, transformer phase shifts, voltage regulators, PV nodes, capacitor banks, and spot or distributed loads with any type and connection are considered. Solution of unbalanced radial feeders shows that the proposed hybrid algorithm Is accurate.

An Approach to Determine a Pair of Power-Flow Solutions Related to the Voltage Stability of Unbalanced Three-Phase Networks

This paper proposes an approach to determine a pair of power-flow solutions associated with the voltage stability of unbalanced three-phase networks. The approach is derived from the observations of the multiple three-phase power-flow solutions of a two-bus network. It is found that there are two pairs of solutions at the load bus. The plot of the voltage magnitude of each pair against the power demand at the load bus shows that two possible PV curves can be constructed for each phase. Each of the two curves is a combination of the two pairs of solutions. One of these curves is associated with the voltage stability of the system whereas the other is associated with the imbalance of the three-phase network. Based on the above observations, a constant impedance load model is utilized to calculate the solution associated with the voltage stability of the study system. Then the equivalent complex power load demand is used to calculate the two pairs of solutions, i.e., the multiple three-phase power-flow solutions. Simulation studies have been carried out for the multiple solutions. The results show that there is a point which is directly proportional to the imbalance in the power demand at the load bus. This point is used to set a criterion to differentiate between the two PV curves. Hence, the PV curve which is related to the voltage stability can be determined without the assumption of the linear load model at the start of the study.

Analysis of three phase distribution networks with distributed generation

This paper presents three phase distributed generations (DGs) model in unbalanced three-phase distribution power-flow and analyzes their effect when they are connected in distribution networks. The DGs can be modeled as a voltage-controlled node (PV node) or as a complex power injection (PQ node). The unbalanced three-phase distribution power-flow has been developed on the basis of the symmetrical components. Newton Raphson method has been chosen for well known excellent convergence characteristics. The three-phase power-flow program has been tested using a practical 37 node distribution feeder. The solution of the base case of the 37 node feeder is compared with the radial distribution analysis package (RDAP). Then the three-phase power-flow method is used to analyze distribution networks with DGs. The analysis is carried out with various size, quantity and location of DGs. The simulation results show that the integration of DG into an existing distribution network can improve the voltage profile as well as reduces the total system losses.

Optimal size and location of distributed generation unit for voltage stability enhancement

This paper presents the analysis of a distribution system connected with distributed generation (DG) units. The developed technique is based on the steady state voltage stability index. The weakest branches in the distribution system which are more likely go to the instability region are selected for DG allocation. Two optimization methods are utilized to find out the size of the DG corresponding to minimum losses or minimum stability index. The Newton-Raphson load-flow is used to find the steady-state solution of the studied distribution system. The AMPL software package is utilized for evaluating the size of the DG units. The developed methods are tested using a 90-bus distribution system with a variety of case studies.

Efficient three-phase power-flow method for unbalanced radial distribution systems

this paper presents an efficient three-phase power flow algorithm for distribution network analysis. A new transformer model with various connections is implemented in the forward/backward sweep power flow method. The developed method provides an effective solution to the singularity problem of the nodal admittance submatrices appeared in some transformer configurations. Different load models and capacitor banks are also implemented with any number of phases and any connection. The proposed load flow has been tested using both the IEEE 4 and 34 node test feeders. The obtained results show that the proposed load flow is very efficient and the numerical solution is identical to that provided with the IEEE data.

Parallel sequence decoupled full Newton-Raphson three phase power flow

A three phase power flow program based on symmetrical components comprises three independent subproblems corresponding to positive, negative, and zero-sequence networks. The positive sequence network is solved using sequence decoupled full Newton-Rahpson method without any modifications in their formulation. The negative- and zero-sequence networks are solved using nodal voltage equations. These three sequence networks have been modelled by three independent equivalent circuits and solved simultaneously using multi-core processors parallel programming. The parallel three-phase power-flow program has been tested using IEEE 13, 34 and 123 node feeder and a practical 37 node distribution feeder. The result showed that parallel three phase load flow produced execution speedup for every test system.

Grid-connected Photovoltaic models for three-phase load flow analysis

The paper presents grid connected Photovoltaic (PV) models for three-phase distribution load flow analysis. The models comprises of single-diode PV model with and without the effect of the series and parallel resistances, I-V nonlinear question, I-V database and single-phase PV modeled as singlephase real power injection. The three-phase load flow program with Photovoltaic models has been tested using IEEE 13 node feeder. The solution of the base case is compared with the radial distribution analysis package (RDAP) before used to analyze distribution networks. The analysis is carried out with various photovoltaic mathematical models. The simulation results show that the grid-connected three-phase photovoltaic system in distribution network can improve the voltage profile as well as reduce the total system losses. However, single-phase PV DG model does not always guarantee voltage improvements.

Analysis of hybrid photovoltaic and wind energies connected to unbalanced distribution systems

This paper presents a steady state analysis of allocation of photo-voltaic and wind generation units in electrical distribution networks. A complete steady state models for PV energy power generation systems for power flow applications is applied. In addition, a new model for the induction generator for wind generation unit will be presented. These models are driven without any assumption and by taking into consideration complete generation system equivalent circuits parameters. It is noticeable that the input data for these driven models are only the environmental conditions. In addition, different load models, capacitor banks, distribution transformer and voltage regulators are also implemented with any number of phases and connection. This Analysis is performed to identify issues that will be most relevant to engineers working in planning and operations of distribution systems with installed distribution generation. Comprehensive tests are applied on 123 node IEEE distribution test system.

Sizing and locating distributed generations for losses minimization and voltage stability improvement

The paper presents analysis of distribution system connected with distributed generations. The study addresses aspects related to optimal sizing and location of DG units for losses minimization and voltage stability improvements. Many cases have investigated to highlight the relationship between the optimum size and location for losses minimization and the optimum size and location for stability improvements. The student version of the AMPL software is used in the proposed study. The objective function is formulated with full consideration of both quality and inequality constraints. On the other hand, the stability index criterion is used for calculating the best location and size for system stability improvements. The 90 bus test system from the literature is used for the different studied cases. The results show that calculating minimum system losses is not necessary to achieve coherence improvement for the voltage stability problem.