D
DB
We appear to be making a complex topic out of a simple situation. First generators are not smart machines and only obey the laws of physics. When we have a generator running under load and we appy more load the resistance of the system goes down as resitance goes down current goes up. If the generator current goes up and we maintain the same torque the voltage has a tendancy to fall. Exciters (AVRs) correct this but frequency still goes down unless we apply more speed (fuel/torque). If we have have no magnetic field we have no voltage, if we over excite (more voltage) we produce extra VARs if we under excite (less voltage)we accept VARs. The changing of the strength of the magnetic field (excitation) creates a stronger magnetic field which keeps trying to force the two different magnetic poles to stop in one position creating a speed drop (load on the prime mover). We must thefore increase the fuel into the system to maintain the same frequency. If we add more fuel it creates heat and is restricted in its flow out of the system, so we in turn create higher temperatures (the gases need to escape faster). Our modern controllers do all of the adjustments automatically not so complex.