Thermal Design Optimization of a New Solid State Current Limiter Design For Smart Grid Applications

Thermal Design

As new independent power suppliers, such as alternative energy suppliers, are integrated into the existing power distribution systems, the likelihood of fault currents increases. Additionally, as power demand increases, the expected fault current levels are increasing to the point that existing buswork and switchgear are not rated for the higher levels. The SSFCL uses advanced power semiconductor devices to interrupt the current flow in the main circuit and insert an energy absorbing resistor into the flow path. 

The Solid-State Fault Current Limiter (SSCL) is considered to be an integral part of renewable energy integration into the existing power grid and a crucial piece of equipment for implementation of the envisioned “smart grid”. In steady-state operation, the fault current limiter continuously anticipates a fault by the use of power electronics. These power electronics are solid-state switches that act rapidly to protect sensitive equipment from a massive current. When fault occurs, the switches direct the larger current to a set of variable resistors as well as a set of inductors. The inductors act to step down the current such that normal operating conditions are sustained. 

In both steady-state and fault operation, the thermal management of the power electronics and inductors is challenging. This study focuses on the effects of five parameters that affect heat transfer as well as the overall size of the SSCL system in steady-state operation. The five parameters studied here are: stack separation, SGTO module block separation, volume flow rate, the inclusion/neglect of natural convection and the power dissipation of each SGTO module block. 

To explore the effect of these parameters, a Six-Sigma Design of Experiments methodology is employed and the resulting matrix is used to change each parameter in the Computational Fluid Dynamics/Heat Transfer (CFD/HT) software IcePak. It was found that flow rate, stack separation and required heat dissipation were the most influential parameters on SGTO module operating temperature.