• Title, Summary, Keyword: Capacitively graded bushing

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Simulation of Capacitively Graded Bushing for Very Fast Transients Generated in a GIS during Switching Operations

  • Rao, M.Mohana;Rao, T. Prasad;Ram, S.S. Tulasi;Singh, B.P.
    • Journal of Electrical Engineering and Technology
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    • v.3 no.1
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    • pp.36-42
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    • 2008
  • In a gas insulated substation (GIS), Very Fast Transient Over-voltages (VFTOs) are generated due to switching operations and ground faults. These fast transients are associated with high frequency components of the order of a few hundreds of MHz. These transients may cause internal faults i.e., layer-to-layer faults or minor faults in a capacitively graded bushing, which is one of the important pieces of terminal equipment for GIS. In the present study, the PSPICE model has been developed to calculate the voltage distribution across the layers of 420kV graded bushing for high frequency pulses of rise time 1 to 50ns, which simulate the VFTO. For this simulation, an equivalent electrical network of bushing with different equivalent layers has been considered. The effect of different equivalent layers modeling circuits on the non-uniform voltage factor has been analysed. The influence of copper strip inductance on voltage distribution across layers has also been analysed for various rise times of high frequency transients. Finally, the leakage current of the bushing is calculated for evaluating the bushing condition under these transients.

Computer Aided Identification of Inter-Layer Faults in Gas Insulated Capacitively Graded Bushing during Switching

  • Rao, M.Mohana;Dharani, P.;Rao, T. Prasad
    • Journal of Electrical Engineering and Technology
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    • v.4 no.1
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    • pp.28-34
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    • 2009
  • In a Gas Insulated Substation (GIS), Very Fast Transients (VFTs) are generated mainly due to switching operations. These transients may cause internal faults, i.e., layer-to-layer faults in a capacitively graded bushing as it is one of the most important terminal equipment for GIS. The healthiness of the bushing is generally verified by measuring its leakage current. However, the change in current magnitude/pattern is only marginal for different types of fault conditions. Leakage current monitoring (LCM) systems generate large amounts of data and computer aided interpretation of defects may be of great assistance when analyzing this data. In view of the above, ANN techniques have been used in this study for identification of these minor faults. A single layer perceptron network, a two layer feed-forward back propagation network and cascade correlation (CC) network models are used to identify interlayer faults in the bushing. The effectiveness of the CC network over perceptron and back propagation networks in identification of a fault has been analysed as part of the paper.