I understand that reactive power injection can be used by generators to support the grid voltage when sagging, but I’ve never understood why this works. I thought it could be charging transmission line capacitance or something, but I can’t make sense of it when I try to follow through with this starting point.
I’ve seen similar questions on here with great answers. In Why is it desirable to inject reactive power into a transmission system? the answer explains how capacitive compensation on the transmission line can reduce the reactive power draw from a generator to power a partially-reactive load, ultimately explaining why reactive power is relevant in a power system. In Why does reactive power affect voltage? the answer from Olin explains how a reactive load can draw additional current from a generator and result in real power loss and voltage drop across the transmission line. I am guessing there is enough info from these answers that I could be able to come to an answer to this question, but I think I need some spoon-feeding.
The assumption in my question is that reactive power injection from a generator supports grid voltage. Is this generally true? If so, could someone help me understand how reactive power injection can be used to raise a sagging grid voltage, or the voltage at a local bus? Are there truths or assumptions made about the grid’s loads and lines in doing this?