How to alter the voltage set points of conventional generators to ensure they are not at their reactive power limit?

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I've solved a case in PSSE however, a number of my conventional generators are at their Qmax.

I am aware that changing the Voltage Set Point can reduce my Qmax, however, after I alter this on one unit it knocks it off on a different unit.

How do you decide on the correct Voltage Set Point of a generator? Is there a method for doing this?

Additionally, sometimes when I change the Voltage Set Point and re-solve the case the system blows up.

Any advice would be appreciated.