New current transformer using SF6 and compound support insulation systems

With the use of SF₆ insulation for bar-type primary current transformers there are three parallel insulation systems which must be properly coordinated dielectrically. It is shown that by the careful design of internal geometries and the selection of correct materials, coordination can be achieved for all conditions of lightning impulses, switching impulse and power frequency voltages. This results in a lightweight, compact current transformer that has large safety margins and is economical to manufacture. To show the performance of the unit, the effects of internal insulation faults and arcing at full short-circuit currents of 63 kA RMS are investigated