This thesis describes an effective method to suppress and control d.c. corona of coaxial gas insulating systems using resistive barriers fitted to the central conductor. Charging of these barriers reduced the field strength at the central conductor transferring the high field region to the barrier surfaces. If this field exceeds the corona inception value the discharge is limited by the resistivity of the barrier system. Various geometries were investigated some of which gave a significant improvement in corona performance. For example the corona onset voltage of a coaxial electrode system (1.6cm/58.1 cm diameter) was increased by 75% when three high resistive rods were fixed around the central conductor. In addition, a cylindrical barrier placed around the central conductor was tested. This gave a better corona performance than the rods previously used. A computer program based on the finite element method was developed in order to illustrate the basic operation of the barrier arrangement and support the experimentation in determining some of the system parameters. Correlation betwe_n experimental and computation results of electric stress distribution in the system was also performed. This thesis also describes an iterative method used using the computer program to perform the numerical integration of the equation which gave the number of electrons in an avalanche along the maximum flux line. This enabled the calculation of the critical size of avalanche which in turn gives the corona inception voltage for the system. The study was extended to include the effect of the barrier arrangement in the SF6 gas insulating system. Moreover, experimental tests and computer calculations were carried out to study the effect of protrusions on the barrier arrangement. Finally computer aided design was performed to optimise the maximum electric stress on the surface of central conductor and the barrier for various barrier voltages and goemetries.