Systematic Analysis and Characterization of Extreme Failure for IGCT in MMC-HVdc System—Part I: Device Structure, Explosion Characteristics, and Optimization

Explosion proof of power devices is important for the safe operation of high voltage direct current power transmission system based on modular multilevel converter (MMC-HVdc). Comparison of the main commercial power devices' structures shows that the integrated gate commutated thyristor (IGCT) has the simplest housing structure, which is suitable for withstanding the extreme fault in the MMC-HVdc system. Explosion proof tests of IGCT are carried out with different distribution of destruction positions under the extreme failure in the MMC-HVdc system. The maximum surge current of IGCT is between 600 and 700 kA when 18 mF capacitor with 4500 V is discharged. IGCT with evenly distributed destruction positions shows excellent explosion proof, while IGCT with edge focusing destruction positions shows poor explosion proof. Further thermal analysis with simulation shows that IGCT's ceramic shell may suffer a huge transient thermal stress when the destruction positions focus on the edge areas. A designed gas pressure tolerance test shows that the gas pressure is in the safe area which IGCT can withstand under the extreme failure. This means that the thermal stress can be regarded as the main cause of IGCT's explosion phenomenon. Based on the explosion mechanism, an optimized IGCT with controlled punch-through design in the central area is proposed to avoid the edge area destruction under the extreme failure. And explosion proof experiment of optimized IGCT validates its excellent explosion proof under the extreme failure in the MMC-HVdc system.