Development of specifications for a thermal buffer device

This paper looks at the operation of metal oxide varistors (MOV) in a hybrid fault current limiting and interrupting device (HFCLID), wherein, the MOV is required to take the burden for an extended time (increased number of cycles) and repetitively. In such a case the heat generated in the MOV as a result of absorption of the fault current, would be too high for conventional heat sinks. If the absorbed energy is not dissipated effectively thermal runaway or mechanical damage of the MOV may result. A thermal buffer with high heat transfer rate, can provide a short thermal path for the effective dissipation of the heat and reduce/eliminate the damage to the varistor. The thermal buffer can be achieved by using heat pipes and/or with appropriate phase change material. This idea is tested by simulating a typical model of a varistor and subjecting it to the required inputs. A finite element analysis package is used to run the simulations and the mechanical and thermal effects are considered by using a non-linear transient coupled thermomechanical analysis. The understanding of the transient thermal dissipation demand allows the thermal buffer capacity to be specified.