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

  • Rao, M.Mohana (Bharat Heavy Electricals Limited, Corporate R&D, India) ;
  • Rao, T. Prasad (Jawaharlal Nehru Technological University, India) ;
  • Ram, S.S. Tulasi (Jawaharlal Nehru Technological University, India) ;
  • Singh, B.P. (Bharat Heavy Electricals Limited, Corporate R&D, India)
  • Published : 2008.03.01


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.


  1. J. Meppelink, K. Diederich, K. Feser and P. Pfaff, 'Very Fast Transients in GIS', IEEE Trans. Power Delivery, vol. 4, no. 1, pp. 223-233, Jan. 1989
  2. M. Mohana Rao, M. Joy Thomas and B.P. Singh, 'Frequency Characteristics of Very Fast Transient Currents (VFTC) in a 245 kV GIS', IEEE Trans. Power Delivery, vol. 20, no. 4, pp. 2450-2457, Oct. 2005
  3. S. Yanabu et al. 'Estimation of Fast Transient Overvoltages in a Gas Insulated Substation', IEEE Transactions on Power Delivery, vol. 5, no. 4, pp. 1875-1881, 1990
  4. E. Kuffel, W.S. Zaengl and J. Kuffel, High Voltage Engineering Fundamentals, Second Edition, Newnes Publishing Ltd
  5. H.M. Ryan, High Voltage Engineering and Testing, IEE Power Series 17, Peter Pergrinus Ltd
  6. A. Ardito, R. Torio and G. Santagostino, 'Accurate Modeling Of Capacitively Graded Bushing For Calculation Of Fast Transient Over Voltages In GIS', IEEE Transactions on Power Delivery, vol. 7, no. 3, pp. 1316-1327, July 1992