NSTX toroidal field coil turn to turn short detection

The National Spherical Torus Experiment (NSTX) was designed, installed, and commissioned in the existing facilities at Princeton Plasma Physics Laboratory (PPPL) in 1999. Most of the hardware, plant facilities, auxiliary subsystems, and power systems originally used for the Tokamak Fusion Test Reactor (TFTR) were used with suitable modifications to reflect NSTX needs. A major upgrade was undertaken on NSTX. The TF has been upgraded to provide one tesla field from the present 0.5 tesla field. This entailed a much higher Toroidal Field Current from 71.2kA to 129.8kA, and required major configuration changes including doubling the number of parallel strings of rectifiers along with associated power loop changes. Before the planned upgrade the machine developed turn to turn fault of the Toroidal Field Coil bundle. The machine was shut down and the Upgrade work started earlier than planned. It was decided to provide a turn to turn fault detection and trip for the upgraded toroidal field coil. A unique scheme was developed to detect a turn to turn fault in TF. This paper gives a description of the turn to turn short detection scheme that has been implemented.