M.A. Mostafa

A computational comparison of steady state load shedding approaches in electric power systems

This paper presents a formulation of the optimal steady state load shedding problem that uses the sum of the squares of the difference between the connected active and the reactive load and the supplied active and reactive power. The latter are treated as dependent variables modelled as functions of bus voltages only. An investigation of the performance of the proposed algorithm over a range of generation deficits as well as overload conditions is presented. Testing is done using IEEE 14, 30, 57, and 118 bus power systems, representing small and medium power systems. The optimal results are compared with results obtained using two earlier approaches. The results obtained using the proposed approach appear to give a better optimal state of the power system.

Effects of harmonic distortion on the active and reactive power measurements in the time domain: a single phase system

A new application of the least error squares (LES) estimation algorithm is given for identifying, in the time domain, the active and reactive power from available samples of voltage and current waveforms. The digital available instruments used to monitor active, reactive and apparent power use such samples. A new definition for the active reactive and apparent power for sinusoidal and nonsinusoidal waveforms is discussed in this paper. It is shown that misleading reactive power compensation could be obtained if the circuit power factor is not well defined. Simulated results are presented for different waveforms, where the authors compare the results obtained with other available techniques.

Kalman filtering algorithm for electric power quality analysis: harmonics and voltage sags problems

Power quality involves how close the voltage waveform is to being a perfect sinusoid with a constant frequency and amplitude. In this paper, we review the applications of linear Kalman filtering algorithm on-line for electric power quality analysis. These applications include the measurement of harmonics and voltage sags. Mathematical models for each problem are developed to suite the filter and tested using simulated examples. Conclusions are drawn at the end of the text.

On-line estimation of transformer model parameters

The conventional method for determining the parameters of the transformer is to performing the open and short-circuited tests. The method is only suitable for off-line application. This paper presents an alternative approach to conventional open and short-circuit test for determining the parameters of N-windings transformer operating at power frequency on an on-line mode. This approach is based on linear least errors square (LES) algorithm and uses the digitized samples of the input current and voltage as well as the output current and voltage of the transformer windings. The proposed algorithm estimates the winding parameters in two steps; while in the first step the algorithm identifying the winding parameters, in the second step, the algorithm identifying the core parameters. The proposed algorithm is applied to a two-windings transformer and simulated results are reported in this paper.

Steady-state load shedding schemes: a performance comparison

Abstract This paper presents a formulation of the optimal steady-state load shedding problem that uses the sum of the squares of the difference between the connected active and reactive load and the supplied active and reactive power. The latter are treated as dependent variables modelled as functions of bus voltages only. The equality constraints associated with the power system load curtailment problem are the power flow equations in polar form utilizing the nodal admittance matrix approach. The inequality constraints are characterized by limits on line flows, voltage magnitudes and angles, and active and reactive power generations. The MINOS nonlinear optimization package is used to implement the optimization process. Testing is done using IEEE 14- and 30-bus power systems, and results obtained. The optimal results are compared with results obtained using two earlier approaches. The results obtained using the proposed approach appear to give a better optimal state of the power system.

A study of estimation techniques for frequency-relaying applications

This paper presents an evaluation and performance comparison of two estimating algorithms used for frequency-relaying applications. The first algorithm is based on least squares (LS) error estimation, while the second is based on the least absolute value (LAV) approximations. Two models for frequency estimation, namely the constant-frequency model (CFM) and the variable-frequency model (VFM), are used. CFM is used to measure the steady-state frequency deviation, while VFM is used to measure the transient frequency and its rate of change. For the constant-frequency model, which is suitable for use in microprocessor-based relays, the algorithms are tested using two data sets. The first involves a pure sine waveform, and the second is a wave generated from the electromagnetic transients program (EMTP) simulating a study system. The EMTP is used to generate the corresponding voltage samples at a relay location. Fault conditions applied on the study system to generate distorted waves with and without frequency deviations are considered. For the variable-frequency model, the algorithms are tested using a data set generated from a pure sine waveform. The effects of sampling rate, sample window size and bad data on the performance of each algorithm are studied. A comparison of the results is offered to evaluate the two techniques.

Evaluation of system reliability using seasonal and random operation techniques

The target of any power system is to deliver stable, clean and cheap electrical power to the customer. This paper offers two independent approaches to simulate the operation of the generating units in a power network. The first methodology depends on the load variation in each season while the other one is random through a certain sequence. Using the proposed approaches a comparison between the different suggested PDF that describes the failure and repair for any component is made. The simulation is done based on Monte Carlo method through a small radial system and the IEEE 13 node test system.

Load flow solution of radial distribution feeders: a new approach

This paper presents a new method for solving the load flow problem for radial distribution feeders, without solving the conventional well-known load flow methods. The algorithm procedures are introduced in details. Two radial distribution feeders are solved as a case of study. Tables of voltage, injected powers for each node in the feeder and line losses are presented with comments and conclusions. As a check, the method has been applied on some feeders that have been studied earlier by some other methods and results have been compared. Voltage stability is also checked for the two feeders.

Optimal dynamic load shedding using a Newton based dynamic algorithm

This paper presents a reformulated optimal load shedding policy that takes into account generator control effects and voltage and frequency characteristics of loads. A dynamic problem is formulated with power generation considered as a dependent variable. The equality constraints associated with the load curtailment problem are the power flow equations in polar form utilizing the nodal admittance matrix approach. The inequality constraints are characterized by flexibility limits on line flows, voltage magnitudes and angles, and reactive power generations. The MINOS nonlinear optimization package is used to implement the reformulated problem. Numerical results obtained for the IEEE 14- and 30-bus test power systems are discussed.

Implementing distributed generation to mitigate under-frequency load shedding

This paper proposes a strategy for employing distributed generation units to stop the frequency deterioration resulting from severe disturbances in electrical distribution systems rather than relying on load shedding as the obtainable treatment. Also, sufficient comparison is made between both treatment methods. Low order system frequency response model (SFR) is used to estimate the frequency deviation. The model parameters are adjusted when the system is equipped with the distribution generation units. The amounts of load to be shed or the power to be delivered by DGs are compared and the treatment method that presents better dynamic response specifications is recommended.