RETROFIT OF OUTDOOR MEDIUM VOLTAGE CIRCUIT BREAKER WITH ECO-FRIENDLY GAS TO REPLACE SF 6

Abstract

In this paper, some stages of the assessment for the replacement of sulphur hexafluoride (SF6) with the fluoronitrile (C4F7N) and carbon dioxide (CO2) mixture in a medium-voltage vacuum interrupting circuit breaker, HORIZON 38kV Outdoor Circuit Breaker manufactured by BRUSH Switchgear, is presented. The circuit breaker volume is filled with the fluorinated gaseous mixture and tested for both basic lightning impulse and short duration power frequency withstand following the recommendations of the relevant standards. It should be noted that some crucial modifications were made to the design to suit the new gas mixture under test. Prior to the test campaign, a series of electric field computations were performed, using a commercial finite element method (FEM) software package, to ensure that a safety margin from the critical electric field values is maintained and identify areas of excessive electric field stress that can be potentially improved. Data on the properties of the fluoronitrile compound and its mixture with CO2 is presented. Initial test results demonstrate that the more environmentally friendly gaseous mixture of 20% fluoronitrile content offers satisfactory insulation withstand performance, indicating its suitability from an insulation performance perspective.