Do I take this into consideration? If so how do I size wire in a building with a safety generator? What is my "Ze" when the supply switches from DNO to the safety generator? How do diesel generators behave during faults?
davezawadi (David Stone):
<snip>... These are permanent magnet alternators and probably on very small machines with oversized engines. A short circuit on a conventional (synchronous) alternator will remove the voltage from the AVR (which is powered from the output terminals in most designs), thus removing most of the magnetic field from the rotor. This is a deliberate safety feature to prevent winding damage and mechanical failure. All the other details there suggest that these machines are intended to live a hard life outside, The data missing is how the voltage control works, although there could be some clue from the pilot-excited phrase suggesting that the permanent magnets only give some of the rotor field, the rest being from an AVR. <snip>
I suspect it is more like one of these.
The permanent magnet part is really only a big brother of a bicycle dynamo in that it provides the 'pilot power' that is AC that is then rectified to provide DC power to the electronics in the AVR controller that is setting the Exciter field, and perhaps to supply some ancillary electronics for engine management and cranking battery condition as well. The AVR senses voltage and current readings from the outbound phases to decide exciter level, but is not depending on it for the excitation power to the armature.
The fact that the AVR does not lose its supply when the output voltage collapses is both a benefit and a risk, as you point out, depending on the avr details it keeps going in fault state, but it also recovers more gracefully with spiky loads
The bigger machines by Brush all work on this basis.
It does also mean that clever microprocessor controls and telemetry stay up as well, and cannot be crashed by load side abuse, and that is essential in some more automated settings when either motoring in extra generation or generator shedding from afar.
Mike.
davezawadi (David Stone):
<snip>... These are permanent magnet alternators and probably on very small machines with oversized engines. A short circuit on a conventional (synchronous) alternator will remove the voltage from the AVR (which is powered from the output terminals in most designs), thus removing most of the magnetic field from the rotor. This is a deliberate safety feature to prevent winding damage and mechanical failure. All the other details there suggest that these machines are intended to live a hard life outside, The data missing is how the voltage control works, although there could be some clue from the pilot-excited phrase suggesting that the permanent magnets only give some of the rotor field, the rest being from an AVR. <snip>
I suspect it is more like one of these.
The permanent magnet part is really only a big brother of a bicycle dynamo in that it provides the 'pilot power' that is AC that is then rectified to provide DC power to the electronics in the AVR controller that is setting the Exciter field, and perhaps to supply some ancillary electronics for engine management and cranking battery condition as well. The AVR senses voltage and current readings from the outbound phases to decide exciter level, but is not depending on it for the excitation power to the armature.
The fact that the AVR does not lose its supply when the output voltage collapses is both a benefit and a risk, as you point out, depending on the avr details it keeps going in fault state, but it also recovers more gracefully with spiky loads
The bigger machines by Brush all work on this basis.
It does also mean that clever microprocessor controls and telemetry stay up as well, and cannot be crashed by load side abuse, and that is essential in some more automated settings when either motoring in extra generation or generator shedding from afar.
Mike.