The OLTC Controller

 The controller for this coil was provided by Steve Conner. He had some PCB's left over from his OLTC II, so he sent me one for a very minimal cost.

The capabilities of this circuit are amazing.

The Rogowski Coil.

 The other side of the inner tap.

 The finished Rogowski coil and an attempt to replicate Steve's circuit on a breadboard.

These 2 shots show the importance of the rogowski coil. The shot on the left is with the rogowski coil connected backwards. The IGBT is turned off while there is a large amount of current still flowing, creating a large voltage spike. If this was at full power, the voltage spike could easily kill the IGBT. The shot on the right shows the IGBT turning off at the correct time.

Steve's circuit also has a crowbar circuit which monitors the voltage across the IGBT. If the voltage goes over the set limit, it will turn the IGBT on continuously and short out the power supply, which should trip the circuit breaker.   

more pictures coming soon.