ARJ Volume 106 No 1
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Table of Contents (1.9 MB)
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1. Multiple-Access Interference of Gold Codes in a DS-CDMA System
2. General Fault Addmittance Method Solution of a Line-To-Ground Fault
3. A New Framework for Day-Ahead Electricity Market Based on Information Transparency Before Market Settlement
4. Effect of Temperature Variations on Wave propagation Characteristics in Power Cables.
MULTIPLE-ACCESS INTERFERENCE OF GOLD CODES IN A DS-CDMA SYSTEM
by O.B. Wojuola and S.H Mneney.
Abstract: Properties of spreading codes constitute a limiting factor on the performance of DSCDMA systems. In this paper, we investigate the performance of certain sets of Gold codes in a multi-user DS-CDMA system, from a few users to full system load. Simulation results show that as the system load increases, BER graphs of all the codes maintain their steep high-SNR slopes, with no emergence of error floor or significant system saturation. The results indicate that certain sets of Gold codes have good cross-correlation properties that make them resistant to multiple-access interference, making them more suitable for multiple-access applications.
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GENERAL FAULT ADMITTANCE METHOD SOLUTION OF A LINE-TO-GROUND FAULT
A NEW FRAMEWORK FOR DAY-AHEAD ELECTRICITY MARKET BASED ON INFORMATION TRANSPARENCY BEFORE MARKET SETTLEMENT
by J.D. Sakala and J.S.J Daka.
Abstract: Line-to-ground faults are usually analysed using symmetrical components. For this type of fault the sequence networks are connected in series and solved to obtain the sequence currents and voltages at the fault point. These are then used to determine the symmetrical component voltages at the other bus bars and the symmetrical component currents in the lines. The phase quantities are obtained by transformation. In this approach, the connection of the sequence networks must be known for the fault. In contrast, the solution by the general method of fault admittance matrix does not require prior knowledge of how the sequence networks are connected. It is therefore more versatile than the classical methods. It does however require the fault admittance matrix at the fault point. For a line-to-ground fault, of zero impedance, the fault admittance matrix is infinite and has to be simulated. The paper presents a procedure for simulating the short circuit, a requirement for using the general fault admittance method. The results obtained are as accurate as those obtained using the classical approaches.
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by H. Moazzen and M.T. Ameli.
This paper studies the impact of information transparency on power market; the importance and the advantages of the information transparency in power markets are described. Market price before market settlement is considered as released information and a new mechanism for observable day-ahead market is proposed. In this mechanism, participants’ bidding and the market clearing model are performed in an iterative procedure which consists of a number of market rounds. The round with the most social welfare is proposed as the market settlement round. GENCOs bid using market price forecasting method. To take into account the released information, a decisionmaking method is presented. A six-bus test system is employed to illustrate the proposed method. The numerical results show the impact of information transparency on the market indexes. As a result, it is found that higher information transparency leads to a decreased market price and it can improve market efficiency and stability.
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EFFECT OF TEMPERATURE VARIATIONS ON WAVE PROPAGATION CHARACTERISTICS IN POWER CABLES
C. Nyamupangedengu, M. Sotsaka, G. Mlangeni, L. Ndlovu and S. Munilal
Abstract: Partial discharge (PD) mapping and fault location in power cables are techniques based on the principle of time domain reflectometry (TDR), a phenomenon that in turn depends on the high frequency wave propagation characteristics of the power cable. Furthermore, power cables are increasingly being used to simultaneously convey electric energy as well as communication signals in technologies such as smart grids. In operation, power cables experience wide ranging temperature variations due to changes in the load current flowing through the cable. It is therefore necessary to understand the effect of temperature variations on the high frequency characteristics of power cables.
Simulations and experimental tests performed in this study show that temperature variations introduce errors in TDR measurements. It is also shown that when temperature in the cable changes from 22°C to 58°C, attenuation increases by one order of magnitude while the propagation velocity increases by an average of 4 %. The phase constant however decreases by an average of one order of magnitude. The implications of the findings are that temperature effects have to be taken into account when designing communication channels in power cables.
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