M.M. Abdel Aziz

A wavelet-based fault location technique for aged power cables

A novel wavelet-based travelling wave cable fault locator scheme is presented in this paper. Using the theory of wavelet singularity detection as a powerful signal processing tool, the initial arrival of the voltage travelling waves at both sides of the power cable and the second arrival of the travelling waves at the first side can be identified reliably without the need for detection the sign of these waves. The developed wavelet processing is applied on the modal coordinated instead of the phase coordinates. The proposed scheme has the ability to eliminate the effect of the change in the propagation velocity of the travelling waves. This will help solving the problem of cable changing parameters especially the changing of the relative permittivity of the cable over its age. Cable changing parameters causes a large error in all fault location techniques, which use the value of velocity of propagation in calculations. Characteristics of the proposed protection algorithm are analyzed by extensive simulation studies using ATP/EMTP. The obtained results indicate an accepted degree of accuracy for the suggested fault locator. In addition, the results prove that the proposed wavelet-based scheme solves the problem of aging cables with changing parameters over the age of the power cable.

Comparison of Shunt-passive and Series-passive Filters for DC Drive Loads

Abstract The existence of harmonics in power systems and their effects have led to opulent issues of electric power quality. In this article, an optimization approach using FORTRAN feasible sequential quadratic programming to maximize the power factor at the DC drive loads terminals is presented using different passive filter topologies. Many constraints are taken into consideration such as series/parallel resonance conditions, effect of the supply frequency, and non-linearities of the supply and the load. Also, a detailed comparison of the simulated results for shunt- and series-passive filters is also presented in this article. The general compensation characteristics and the detailed comparison are discussed by means of different numerical examples from previous publications.

An accurate scheme for fault location in combined overhead line with underground power cable

This paper presents an accurate fault location scheme for transmission systems consisting of an overhead line in combination with an underground power cable. The algorithm requires phasor measurements data from one end of the transmission line and the synchronized measurements at the most far end of the power cable. Fault location is derived using distributed line model, modal transformation theory and discrete Fourier transform. The technique can be used on-line or off-line using the data stored in the digital transient recording apparatus. The proposed scheme has the ability to locate the fault whether it is in the overhead line or in the underground power cable. Extensive simulation studies carried out using MATLAB show that the proposed scheme provides a high accuracy in fault location under various system and fault conditions.

On the Economic Selection of Capacitive Compensator Sizes in Nonsinusoidal Conditions

The selection of the optimal capacitor is a multiobjective op- timization problem. An approach to solving a multiobjective optimization problem is to transform it into a single objective problem. In this letter the use of the power factor and the efficiency as constraints is proposed be- cause power factor in distributions systems may be allowed within certain limits such as 0.85 and 1.0 and similarly for the efficiency. Keywords: Harmonics, power factor, power quality. Introduction: Reference (1) discussed the different criteria for the design of the compensating capacitor for the system shown in Figure 1, taking into consideration the skin effect (a) Maximizing the power factor,

Power factor and your electrical utility bill in Egypt

Beside being a good neighbor and not causing harmonic voltage for others that are connected to your electrical distribution circuit, complying with the legal requirements of IEEE standards 519, and maintaining safe and economical operating environments for electrical equipment within your physical load, there is another very good reason to maintain a good power factor: saving money on your electrical utility bill. Utilities often encourage consumers to maintain a high PF by applying tariff clauses, which penalize consumers for low PF. This letter discusses the topic.

Increased Efficiency in the Conversion of Solar Energy to Electric Power

This article presents a new dual purpose technique to improve photovoltaic (PV) array efficiency and has a great effect for the net power saving. To realize the first aim, the forced-air cooling technique with the optimal flow rate for PV array is designed and implemented. The decreasing rate in cell temperature has a direct proportional relation with PV efficiency. At the same time, the output hot air is very useful for air conditioning houses and for heating water systems, especially in remote areas. The electrical performance of PV modules also was studied. Finally, the effect of power saving was cleared and the economical results were achieved.

A New Method for Cable Joints Thermal Analysis

A general analytical method for thermal analysis of a joint in an oil-filled high-voltage cable is presented. Oil flow within the conductor oil duct, longitudinal heat flow through the conductor, and conductor losses variation with temperature are taken into consideration. The method is applied for a straight joint in a 300 kV, 2000 mm2 integral sheath cooled oil-filled cable. The theoretical temperature distributions along the conductor from joint to cable are in good agreement with the corresponding experimental results.

Steady state temperature distribution of high voltage bushings-analysis and measurements

A computer program is developed to perform the thermal analysis of the temperature distribution of the conductor in a high-voltage bushing under steady-state conditions. A thermal circuit for an element of length dx of the conductor is analyzed, and a differential equation representing the thermal performance is obtained. The solution of the equation can be obtained without any prior measurements of conductor temperatures. The analysis is applied to a 69 kV air-to-air bushing with one end immersed in oil as well as to an experimental bushing. Good agreement between predicted and measured temperature distribution is obtained. The locations of hot spots inside the conductor, under different loading conditions, have been calculated with good accuracy. In order to reduce the hot spots, an evaporative cooling method is applied to both bushings and the conductor thermal analysis has been modified to include the cooling effect. >

Skin effect on optimal power factor

Optimization criteria are presented which allow proper calculation of optimal power factor. Optimization minimizes the line loss, maximizes the power factor and maximizes the efficiency, taking into consideration the skin effect. The performance of the obtained capacitor is discussed by means of a numerical example.

Thermal Analysis of Cable Sealing Ends

A general analytical method for thermal analysis of high-voltate oil-filled cable sealing ends is presented. Oil flow within the conductor oil duct, longitudinal heat flow through the conductor and conductor losses variation with temperature are taken into consideration. The method is successfully applied for a sealing end of a 300 kV, 2000 mm2 integral sheath cooled oil-filled cable. A companion paper where cable joints are analyzed, is referenced.