12.6 kA / 20 kV / 300 Hz reverse conducting solid state closing switch for De-NOx / De-SOx modulator

The presentation will discuss the specification, the design, the construction and the test results of a solid state switch which is used in De-NOx/De-SOx modulators. The closing switch is operating at a charge voltage of 20 kVdc with a 300 Hz pulse repetition rate and a 12.6 kA, 12 ¿s exponential decay waveform. In case of arcing in the load the waveform will change to a 250 ¿s damped sine wave. The current rise rate is in access of 10 kA/¿s or more. The paper will show the selection criteria of the semiconductor devices, and the optimization of the devices for this application. The complete ready-to-use switch is built-up with a series connection of eight reverse conducting devices with individual driver units which are optical triggered. This construction results in compact stack with very low self inductance. The switch is capable to operate continuous at a pulse repetition rate of 300 Hz and can be cooled by transformer oil or de-ionized water. Information will also be given on reliability and life expectancy based on tests and earlier produced switches.