Band 7, Heft 2

The increases in power flows and environmental constraints are forcing electricity utilities to install new equipment to enhance network operation. Some application of Flexible AC Transmission System (FACTS) technologies to existing high-voltage power systems has proved the use of FACTS technology may be a cost-effective option for power delivery system enhancements. Amongst various power electronic devices, the unified power flow controller (UPFC) device has captured the interest of researchers for its capability of regulating the power flow and minimizing the power losses simultaneously. Since for a cost-effective application of FACTS technology a proper selection of the number and placement of these devices is required, the scope of this paper is to propose a methodology, based on a genetic algorithm, able to identify the optimal number and location of UPFC devices in an assigned power system network for maximizing system capabilities, social welfare and to satisfy contractual requirements in an open market power.In order to validate the usefulness of the approach suggested herein, a case study using a IEEE 30-bus power system is presented and discussed.

This paper investigates the chaotic behavior exhibited by a typical ferroresonant circuit under two-phase open condition. The circuit includes multiple nonlinear elements that accounts for transformer core nonlinearities and arrester. In most of the ferroresonance studies the core loss of the transformer is neglected or modeled as linear resistor [1]. The basic model of the system under investigation and solution of the differential equations describing the model are corroborated against MicroTran [2]. Choice of state variables and formulation of state equations are accomplished through a topological approach [3]. Extensive simulations have been carried out to analyze the sensitivity of the state variables with respect to degree of core saturation, amplitude of the Thevenin voltage source and the presence of arrester. Time response plots, phase plots, Poincaré maps and conventional bifurcation diagrams are used to analyze the chaotic behavior. The results reveal that the nonlinear model of core loss has a significant effect on the onset of chaos. The simultaneous presence of arrester and nonlinear model of core loss effectively eliminates the chaotic region for lower value of transformer saturation exponent.

This paper presents a flow control approach for the speed control of hydro turbines. Power can be controlled by controlling the rotary motion of the spear valve. In this paper, a flow control based model is proposed for the automatic control of small hydro power plants. In the proposed model, a servomotor is used to control the flow of water by controlling the rotational motion of the spear valve. The spear valve causes a 'continuous' control of the flow of water. `Discrete' flow control is achieved by the use of butterfly gates which are activated by DC motors. The suitability of servomotors for the control of small hydro power plants is discussed and PI controllers are used to further enhance their governing capability. State space representation is used to mathematically model the proposed model. Extensive simulations are performed to analyze the behaviour of the proposed model. Parameter optimization is performed using Artificial Neural Networks.

Presently, there is still a critical shortage of experts to interpret and diagnose problems associated with power system harmonics. Thus, the use of a rule based expert system is proposed for the identification of harmonic sources originating from various single phase nonlinear loads such as uninterruptible power supply, personal computer, fluorescent lamp with magnetic and electronic ballasts, PC monitor and oscilloscope. Identification of harmonics originating from single phase nonlinear loads is implemented by first analyzing the harmonic current waveforms using fractal and fast Fourier transform analyses so as to characterize the harmonic signatures of the different types of nonlinear loads. Then, a rule-based expert system is developed in which the system identifies and classifies the different types of nonlinear loads from the input current waveforms. The expert system with its user interface has been developed in MATLAB and it has been verified with real current measurements. The results obtained prove that the system enables accurate identification of nonlinear loads.

The present paper is concerned with the application of the equations of a saturated smooth air-gap machine to the analysis of the transient behavior of a multi-phase (six-phase) self-excited induction generator (SEIG). In the analytical model (d-q axis model), the effects of common mutual leakage inductance between the two three-phase winding sets have been included. A detailed experimental investigation of self-excitation process, loss of excitation and re-excitation, switching-in of pure resistive load without, and with series compensation (short shunt) is also included in this paper.

It is well known to electricity authority worldwide of difficulty in meeting an ever increasing demand of a rural load center tens to hundred kilometers away from the interconnected grid. In many cases, upgrading sub-transmission system seemed appropriate in technical, economic and environmental aspects. Nevertheless, there are cases where addition of local generation is the only means to meet the increasing demand. For more than ten years, Thailand's Provincial Electricity Authority has been tackling complications of adding more and more local generations until exceeding the local off peak demand. These generations consist of four small hydro, one geothermal and one fuel oil power plants. Unfortunately, the unplanned attempts made to resolve problem concerning provision of electricity supply to meet the demand without conducting any pre-engineering study had proved ineffective and sustainable solution could not be attained. This paper described, analyzed and discussed in details the development of PEA's distribution system planning to supply quality and reliable electricity to a small rural and remote community in the country Northern province. Extensive field surveys and technical analyses were carried out to investigate impacts of distributed generation on the performance of the network. Finally, recommendations were given as guideline for further study in search of feasible and sustainable solutions.

A good grounding system is the fundamental insurance to keep the safe operation of power systems. The grounding resistance reduction additive-fly ash is proposed in this study. Fly ash is the byproduct of coal-fired power plants. A pulverized coal boiler generates approximately 80% fly ash and only 20% bottom ash. Furthermore, the study of these materials will assume greater importance. Waste utilization is an attractive alternative to disposal in that disposal cost and potential pollution problems are reduced. Extensively used as an additive in Portland cement or as a mineral admixture in concrete in recent years, we have found that fly ash has a low resistivity, and so can be used as an agent for reducing resistance to grounding. Also, an effort is made to investigate the effect of water-to-cement(W/C) and temperature on the resistivity of the test specimens. The grounding resistance reduction agent was determined by considering various proportions of water, cement and salt. Experimental results demonstrate that the proposed approach can effectively reduce the grounding resistance.