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This question is not intended to solve an issue but in the hopes of expanding my general understanding. I am an aux. operator working towards Control Room Operator at a simple cycle GE7fa plant and was wondering how the VIGV system works? I'm not interested in the mechanics as that is fairly well understood, but rather in what the operating principle is that makes it function. For example in relation to exhaust temp. control do the IGV's adjust for increased/decreased exhaust/turbine cooling or does it affect air flow or air pressure used in combustion and therefore combustion temp. or is there some other concept that makes VIGV's work. If it helps I work at a 7fa plant with dln 2.6 combustors on gas only.