Structural Strength of PTFE Insulating Nozzles in Circuit Breakers

The insulating PTFE (Polytetrafluoroethylene) nozzles have found their wide application in many medium/high voltage and generator circuit breakers. The main reason for this material selection for the insulating nozzle is the arc ablation resistance of PTFE. The nozzles are directly exposed to the electric arc, which is a very hostile environment, where the temperature can reach several thousand Kelvin. During the sublimation of the PTFE, a lot of the PTFE vapor is generated, which helps to cool down the electric arc. The structural strength of these parts is one of the important factors determining the reliability of the whole device. In breaker applications, the internal pressure load caused by the arc can reach up to 150 bar, which can damage the nozzle and in the worst case, the nozzle can malfunction. The structural analysis has a significant meaning to predict nozzle strength. The FEM simulation presented here is based on a sophisticated PFTE material model with the following non-linear properties: strain rate dependent plasticity, the transition between brittle and ductile behavior under tension and compression loads correspondingly. This material data is obtained by experimental measurements. The scientific background of our research is illustrated by a numerical example from one of the practical applications.