Carbon-polyethelene composites as bench marks for breakdown studies in windings

Abstract: Changes in resonant frequencies of a winding can identify the location of breakdown during impulse tests. This is difficult with a uniform winding. We propose the use of concurrent UHF antenna and winding currents in order to locate breakdown. The work can be extended to identify partial discharge events in dry type transformers.

Abstract: An objective classification of faults that can occur during impulse tests on power transformers is proposed. It includes nonlinear elements, breakdown, and partial discharge events. An analysis of a layer winding, in the time and frequency domains, with these faults shows that current assessment methods must be used with caution. A model reference approach is proposed to distinctly improve recognition in such cases. The method is immune to changes of wave shape and the instant of fault is available by observation.

Abstract: We propose an objective formulation of the impulse analysis problem from a signal analysis viewpoint. The winding response is quintessentially that of a deterministic network to a finite energy signal, with breakdown and partial discharge being inherently nonlinear events. A significant improvement to the acquisition of waveforms is demonstrated by a virtual instrument approach. It retains the advantages of the time- and frequency-domain methods. The drawbacks of the transfer function method are highlighted and a new piecewise linear approach is proposed for analysis. Experiments on a discrete lumped parameter model of the winding are used to validate the PXI based instrument.

Abstract: Experimental results on fault simulations during impulse tests across windings and other specifically designed networks are reported. Both breakdown and partial discharge studies are conducted with digital acquisition of fault records.

Abstract: During the last three decades extensive and worldwide research progress was made with respect to many aspects of percolation phenomena with the advance of computer technology. The physical properties of composites are well expressed as a function of a power law of the distance from the percolation threshold to a volume fraction of a filler with each critical exponent. Electrical properties at high electric fields of composites have not yet been investigated based on the percolation theory in depth. Works on numerical modeling of dielectric breakdown have been done for a random resistor-capacitor network. The aim of this paper is to discuss the dielectric breakdown of carbon black-polyethylene composites based on the percolation phenomena of the composites. The more the dielectric breakdown strength decreases as the more carbon black is loaded. It has been found for the first time that the dielectric breakdown strength of the composites is described by a function of a power law of the distance from the volume fraction of carbon black to the percolation threshold with the critical exponent of /spl nu/ = 0.9.