I'm calculating the critical reactive margin in a system using Q-V curves to prevent voltage collapse. I need to set the minimum voltage level (pu) because the steps in the iteration reach below this threshold. I think if I don't do this, the PSSE converts P and Q loads to constant Z. The other setting I need to change is the 0.5 to 1.5 range in pu for the plants for this same reason.
A QV study is a steady-state test of the grid and it is usually evaluated for 'credible' voltage ranges like 0.9 pu to 1.1 pu. The QV margin if positive, indicates the amount of static capacitors (and then add additional margin) to be added to eliminate the 'voltage collapse' condition. Adjust the min-max range values for your system (A range of 0.5 to 1.5 is not realistic). There is no need to change plant's voltage operating limits. Generating plant should be able to ride-through contingencies that causes voltage changes according to applicable grid code. PV analysis is another test to check how close the system is to voltage collapse.
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