Hi. I am supposed to explain using phasor diagram how change in excitation current affects power factor and active power of the generator. I have a few different values for excitation current, real power and power factor. Basically, increasing excitation current causes decrease in power factor and real power. But what I dont understand is why the real power decrease as well. Hmm, I do understand because P= VIpf. But in textbooks it is always only two scenarios are described. Constant excitation + change in load and constant load + change in excitation. And for changing excitation, the power output is considered constant. So only power factor changes. It is confusing. So the question is. When alternator is connected to infinite bus bar, when changing the excitation current, does the real power change or not? How can I use phasor diagram to show that?