Problem statement: Power transformer is the most expensive equipment in electrical network; and the mineral oil has the main roles of insulating and cooling in it. Oil is subjected to the degradation because of the ageing, high temperature and chemical reactions such as the oxidation. Then the oil condition has to be checked regularly and reclaimed or replaced when necessary, to avoid the sudden failure of the transformer. It will be very desirable also if we can predict the transformer oil remaining lifetime, from time to time. Approach: An experimental study was accomplished on the used oil specimens coming from several power transformers of various ages, working in Iranian power network, to recognize the correlation between the real age of the oil and the rate of its different characteristics and to know the most appropriate property which can represent its ageing. Accelerated aging experiments were accomplished on oil specimens at different temperatures. Furthermore a method for estimation of the remaining lifetime of the oil, using Arrhenius law, was employed. Results: According to our experiments, it was verified that, by using Celsius degrees and natural logarithm, the Arrhenius law can be applied properly to the thermal degradation phenomena of the oil. Conclusion: It was shown that the presented method can be used to study the degradation of transformer mineral oil and to estimate its remaining lifetime.

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Abstract-The most commonly used weighted least square state estimator in power industry is nonlinear and formulated by using conventional measurements such as line flow and injection measurements. PMUs (Phasor Measurement Units) are gradually adding them to improve the state estimation process. In this paper the way of corporation the PMU data to the conventional measurements and a linear formulation of the state estimation using only PMU measured data are investigated. Six cases are tested while gradually increasing the number of PMUs which are added to the measurement set and the effect of PMUs on the accuracy of variables are illustrated and compared by applying them on IEEE 14, 30 test systems.

In this paper two different multi objective functions are developed. Each one will improve some of the motor characteristics, such as efficiency, power factor, end effect and motor weight. This procedure will be done by analytic method and using particle swarm optimization technique. In this paper a new equivalent circuit model has been used that include all specific effects of single-sided linear induction motors, and a new method will be suggested to evaluate intensity of end effect by help of equivalent circuit method. Results show the accuracy of the equivalent circuit model and the improvement of objective functions at the end of optimization procedure. Two dimensional finiteelement analysis will evaluates the analytical result.Index Terms--Efficiency, End-effect, Finite-element, Power factor.

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