Complex sentence: A valve hall is equipped with installations controlling the temperature of the mercury arc rectifiers or thyristors, which operate best over a narrow temperature range and protect them from adverse weather (rain, ice, snow, dust).
Split into simpler sentences: A valve hall is equipped with installations controlling the temperature of the mercury arc rectifiers or thyristors, which operate best over a narrow temperature range. The valve hall also protects them from adverse weather (rain, ice, snow, dust).