Self protected light triggered thyristors

The prime applications for very high power thyristors are in the utility business sector such as HVDC power distribution and static VAr systems. HVDC systems include not only transmission line installations such as the cross-Channel link with France, but also back to back systems to overcome phase matching problems at interfaces with adjacent facilities. Power levels are typically in the range 500-3000 MW and the inverter/converter equipment required is based on thyristor valves. Individual thyristors of 5-6 kV and 2.5-3.0 kA average rating are connected in series to achieve the line operating voltages of 250-450 kV. Conventional electrically triggered thyristors (ETT) are triggered into conduction and protected against fault conditions, such as overvoltage, by local electronics components mounted on the valve. Command and status data is exchanged with the devices and their associated protective electronics, which operate at the full line voltage, via optical fibres. A SPELTT thyristor would be able to replace the local electronics by integrating the protection functions into the silicon of the thyristor. This will lead to a more robust solution with a corresponding overall cost reduction