Reverse blocking capability of symmetric SCRs at high current and high voltage reversals

Symmetric thyristors with blocking voltages of 2.5 kV have been evaluated under high current conditions in circuits where a reverse voltage is applied to the SCR, caused by a load mismatch in the pulse forming network. The 50 mm diameter SCR was operated in a 45 m/spl Omega/ PFN with a 12.5 m/spl Omega/ load and a shorted load. The peak current switched with the 12.5 m/spl Omega/ load at 1.5 kV was 25.2 kA. The inverse voltage applied to the device was -740 V which was preceded by a voltage spike of 2.2 kV. This spike has a pulse width of 2.5 /spl mu/s and a dv/dt, measured at the 10%-90% points of 875 V//spl mu/s. With the load shorted and an anode voltage 1.4 kV, 29.2 kA was switched with a pulse width of approximately 600 /spl mu/s. The 2.8 /spl mu/s reverse voltage spike under these conditions had a peak voltage of -2.5 kV, a dv/dt of 1.2 kV//spl mu/s and a recovery voltage of -1.1 kV. Data is also presented on 3 SCRs operating in individual PFNs connected in parallel discharging into a common load. This simulates switches operating in the phases of a rotating machine. Data on the characterization and inverse voltage operation of new GE 100 mm SCRs are also presented.