Analysis of self-dual excited synchronous machine. I. Developmentof the general mathematical model and steady-state performanceexperimental verification

The use of the dual excitation system for improving the overall performance of a self-excited synchronous machines is considered, along with the replacement of the compound transformer and rectifier bridge by a potential transformer and thyristor bridge for the self-excitation system. The output DC voltage of the bridge is controlled over a wide range by an automatic feedback control circuit to vary the firing angle of the thyristors in such a way that the terminal voltage is sustained at a constant value. The mathematical models for two distinctive alternatives of the excitation system are derived. The mathematical model thus derived is suitable for transient, dynamic as well as steady-state analysis. However it should be modified to investigate the steady-state and dynamic performance. Exact steady-state operating points are achieved by solving the steady-state equations obtained from the general model. Charts describing the performance of the self-dual excited synchronous machine under steady-state operation for the two alternatives of the excitation system have been calculated at different values of the power factor, i.e., the turns ratio of the transformer and the ratio of field currents. The experimental results obtained on a 7.6 kVA induction machine converted to a d-q synchronous machine confirm the validity and accuracy of the analysis and mathematical models developed     

Probabilistic Studies of Generation Capacity (Part I)

A simplified model is constructed and analyzed to determine the power flow through channels of finite capacity when the supply and demand at the separate nodes are probabilistic. The supplies are generators of different sizes scattered throughout the system; their outages are treated as independent random events. Failure to meet demand is due to forced outages of generators and to inadequate transmission facilities. The model divides an interconnected power system into subsystems and tie lines. It calculates the cost of unsatisfied demand and sudden supply interruption. The difference between generation and demand in the different subsystems is correlated, and this has an effect on the interconnection and reserve requirements. A cost analysis is carried out to obtain the optimum allocation of generators in the model.     

Scaling and Roundoff in Fixed-Point Implementation of Control Algorithms

The analysis and design of digital controllers on microprocessors using fixed-point arithmetic have been considered. Three scaling techniques are applied to the design of digital controllers in such a way as to avoid overflow and to optimize the signal-to-roundoff noise ratio. Both the scaler and the multivariable cases are treated. Statistical estimates of the steady-state roundoff and quantization errors are derived.     

Activation of low dose silicon implants in GaAs by multiply scanned electron beams

Low dose implants of Si+ into semi-insulating GaAs have been annealed with the multiply scanned electron beam processing system. The activation of ions was about 55%, with a high peak concentration and a carrier mobility of 3800 cm2/Vs. The samples were unencapsulated and showed no surface degradation after annealing.     

Sufficient conditions for controllability of a class of distributed parameter systems

In the paper we present certain results on the question of controllability for (i) linear evolution equations (parabolic and hyperbolic) with distributed controls and (ii) a class of linear parabolic equations with boundary controls.     

Block-oriented programmable design with switching networkinterconnect

A block-oriented programmable design with switching network interconnect is proposed for fast turn-around, low manufacturing cost, and layout-independent high-speed systems. We introduce the architecture and investigate the constraints and properties originated from the architecture. We show that routability is the most crucial concern for a successful design, and propose objective functions as well as algorithms for switching network optimization. The mapping for the circuits is performed by partitioning, placement, and routing using a maximum matching method. The integration of the whole system demonstrates excellent results in terms of circuit usage     

Line width control in electron-beam lithography

A method for predicting line widths in electron beam lithography is described. Computer predictions of line dimension as a function of dose, and profile as a function of proximity to another line are compared with experimental results on 0.35?m thick PMMA at a beam energy of 15 keV.     

Isolation of fatty acids from an egyptian petroleum

A mixture of straight-chain fatty acids (from C₇ to C₁₉) was isolated from an Egyptian petroleum via extractive crystallisation with urea. Although the total acidic content in Egyptian petroleum is low, the fatty acids constitute at least 32% of the total acids. n-Pentadecanoic and n-nonadecanoic acids were isolated for the first time from petroleum acids by a sequence involving fractional distillation of the methyl esters, extractive crystallisation with urea and recrystallisation of amide derivatives.     

Power system voltage regulation based on voltage feedback using a dynamic capacitor

Over twenty-four hours of operation of a power system there is a wide variation in the demand, resulting in voltage fluctuation. This fluctuation may be large enough to lead to inefficient and unreliable operation of industrial plants. The fluctuation can be overcome by proper choice of controls (capacitors) located at suitable points on the power networks. To maintain the voltages within tight admissible limits, it is necessary to obtain a complete dynamic model of the generation-transmission system.In this paper, the dynamic model of a power system consisting of a synchronous generator, a transmission line containing four buses, and control capacitors placed at the buses is considered. Two types of control (capacitor) are used to regulate the voltages, (i) a synchronous capacitor and (ii) a static capacitor.A mathematical model of the controls is also presented. In this study, three separate cases of loads at the buses are simulated in the dynamic system. In all the cases the proposed controls are used to regulate the system voltages. The results indicate that, with the variation of loads, the desired voltage regulation can be achieved by proper choice of capacitor controls as functions of time.     

Uncertainty propagation in probabilistic risk assessment: A comparative study

Three uncertainty propagation techniques, namely method of moments, discrete probability distribution (DPD), and Monte Carlo simulation, generally used in probabilistic risk assessment, are compared and conclusions drawn in terms of the accuracy of the results. For small uncertainty in the basic event unavailabilities, the three methods give similar results. For large uncertainty, the method of moments is in error, and the appropriate method is to propagate uncertainty in the discrete form either by DPD method without sampling or by Monte Carlo.