Journal Volume 20 Issue 1

Transients in Transformers with Non-Uniform Inductance and Capacitance Distributions

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Mohamed M. Saied

The electromagnetic transients in transformer windings exhibiting location–depen­dent inductances and capacitances are investigated in the time domain. Analytical functions describing this dependence are assumed and incorporated in the two integro–differential equa­tions governing the transient voltage and current distributions. The boundary conditions are available from the source initiating the transients and the winding’s end termination. Anumeri­cal procedure is applied in order to get frequency domain solutions for the voltage and current in the form of Interpolating and Parametric Functions. The numerical Laplace inversion is then applied to these s–domain expressions. Results pertinent to transients initiated by step- and double-exponential impulse sources are presented and discussed. All possible transformers’ neutral connections are considered. The possible error introduced by neglecting either or both of the inductance and capacitance non-uniformities is addressed. Results indicate that the main error is attributed to neglecting the inductance non-uniformity, whereas the impact of the ca­pacitance non-uniformity is relatively small. In most cases, the winding’s copper and insulation losses have a small effect on the transient response.


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Feasible star – delta and delta – star transformations for reliability networks

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Vishnuvajjula Charan Prasad

Consider the problem of transforming a star (delta) into an equivalent delta (star) in a reliability network with imperfect undirected edges and perfect vertices. It is believed that such transformations are not possible in general if the probabilities of the elements of the given star / delta are rational numbers. Contrary to this, it is shown here that star – delta and delta – star transformations are possible under certain conditions. Further the probability of success of an element of an equivalent star (delta) is shown to be equal to the probability of failure of the corresponding element of the given delta (star).


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