1. The problem statement, all variables and given/known data Consider following: a three-phase synchronous generator which is under excited and drives a load with the power factor of 0.9 . U = 380 V (Main supply voltage) Ia = 75 A Xd = 3 Ω / phase Find the excited voltage E and the load angle δ. 2. Relevant equations Under excited generator -> generator consumes VAr (the load is leading). E can be calculated using various equations and methods, here's an example: E2 = (U + XdIa sin [itex]\phi[/itex])2 + (XdIacos[itex]\phi[/itex])2 Or this one: 3 E2 = (U + XdQ/U)2 + (XdQ/U)2 P = active effects Q = reactive effects For δ an equation like this can be used: P = (3*E*Uf)/Xd * sin δ 3. The attempt at a solution The correct solution should be (my book says so): E = 203 V and δ = 83,3° I get, using all the above equations: P = 44,4 kW , Q = -21,5 kVAr E = 236,1 V and δ = 59° --- Questions: 1. Am I just counting wrong here? 2. In the case of under-excited generator, does the E always have to be lower than per-phase voltage of Uf ? Because in this case I get E > Uf ( 236,1 > (380/√3) ) I appreciate any hints on this one!