Frequency characteristics of very fast transient currents in a 245-kV GIS

The conducted as well as the induced voltages on control cables and control circuits due to transient electromagnetic (EM) fields generated during switching operations in a gas-insulated substation (GIS) depend on the waveshape of the very fast transient overvoltages and the associated very-fast transient currents (VFTCs). The aim of this paper is to build a basis for characterizing the VFTC generated in gas-insulated switchgear and the,associated equipment during switching operations for the study of transient coupling phenomena. The peak magnitudes of VFTC and their dominant frequency content at various locations have been computed in a 245-kV GIS for different switching operations as well as substation configurations. Finally, the influence of the substation layout on the frequency spectrum, dominant frequencies, and the highest possible frequency component of the VFTC at various distances from the switch have been reported.

Two-stream instability in plasma

The problem of two-stream instability in plasma is studied by specifying the importance of initial magnetic field associated with the motion of the charged particles and the boundary effects. In Part I the accurate initial steady state is studied when the streams of electrons and ions move with different uniform speeds in plasmas with plane and cylindrical geometry. In Part II, in order to show the effects of finiteness and inhomogeneity of the system, small transverse plasma oscillations are studied in the case of plane plasmas. The role of plasma-sheath oscillations at the boundaries is found to be very important in driving the instabilities associated with the electromagnetic modes. The numerical estimates of the growth rates of the instability are given for the specific case of the physical data in discharge tubes.