This is getting very confused. The engine will only produce its rated power assuming the frequency (RPM) is constant. All other associated power can only come from the rotating inertia of the engine and generator rotor. A complete short on most sizes of generators will stop the machine very quickly, perhaps 10 or 20 revolutions. The moment the engine speed falls so does its output power, power = torque x RPM, and the torque is limited at all speeds and gets less as the speed falls in most machines at limiting power output. Your document is probably not very accurate for most reasonable-sized generators say <500kVA. Also, the AVR is designed to reduce the excitation if the frequency falls, and usually to make it zero at 40Hz for a 50Hz machine to protect the mechanical parts from failure. The forces involved may be very large, sufficient to break generator shafts, or piston rods or the crankshaft with a low impedance short circuit. Such failures do occur in generator sets sometimes because those first few revolutions are critical, the short circuit current is not in any way "free", it is a real very large amount of power. Just because the short collapses the voltage does not reduce the real power in any way, the alternator is still making 230V or whatever, it is almost all lost in the windings and the external circuit as resistive loss, although perhaps 10% may be lost in the reactance.


I'm afraid Mike has made a slight slip, a synchronous alternator does not suffer "slip" as such, the output exactly follows the machine rotation at all speeds, in the same way that a separately excited motor does. Slip in an induction motor is simply to make the rotor magnetic field, in an alternator, this is externally applied DC and only controlled by the AVR. Small machines do sometimes operate as asynchronous machines but these have very poor overload and voltage control characteristics.


One further point is that most machines that are brushless depend on simulated transformer action to get the AVR excitation power to the rotor, where it is rectified and gives the rotor field. This is a very important part of our size of the machines under discussion. There are a number of various ways to do this, which are usually covered in Patents, it is easiest to just look on this as I suggest, although there may be a secondary alternator action or similar involved. It makes little difference to the operation.

This is getting very confused. The engine will only produce its rated power assuming the frequency (RPM) is constant. All other associated power can only come from the rotating inertia of the engine and generator rotor. A complete short on most sizes of generators will stop the machine very quickly, perhaps 10 or 20 revolutions. The moment the engine speed falls so does its output power, power = torque x RPM, and the torque is limited at all speeds and gets less as the speed falls in most machines at limiting power output. Your document is probably not very accurate for most reasonable-sized generators say <500kVA. Also, the AVR is designed to reduce the excitation if the frequency falls, and usually to make it zero at 40Hz for a 50Hz machine to protect the mechanical parts from failure. The forces involved may be very large, sufficient to break generator shafts, or piston rods or the crankshaft with a low impedance short circuit. Such failures do occur in generator sets sometimes because those first few revolutions are critical, the short circuit current is not in any way "free", it is a real very large amount of power. Just because the short collapses the voltage does not reduce the real power in any way, the alternator is still making 230V or whatever, it is almost all lost in the windings and the external circuit as resistive loss, although perhaps 10% may be lost in the reactance.


I'm afraid Mike has made a slight slip, a synchronous alternator does not suffer "slip" as such, the output exactly follows the machine rotation at all speeds, in the same way that a separately excited motor does. Slip in an induction motor is simply to make the rotor magnetic field, in an alternator, this is externally applied DC and only controlled by the AVR. Small machines do sometimes operate as asynchronous machines but these have very poor overload and voltage control characteristics.


One further point is that most machines that are brushless depend on simulated transformer action to get the AVR excitation power to the rotor, where it is rectified and gives the rotor field. This is a very important part of our size of the machines under discussion. There are a number of various ways to do this, which are usually covered in Patents, it is easiest to just look on this as I suggest, although there may be a secondary alternator action or similar involved. It makes little difference to the operation.