For a machine using field coils, which is most large generators, the field current must be supplied, otherwise the generator will be useless.
12.
But from childhood experimenting with one, my impression is that it does not have a functioning field current adequate to produce much output voltage.
13.
Since both the armature and field current reverse at the same time, the behavior of the motor is similar to that when energized with direct current.
14.
Load dump can be more damaging because the alternator continues to generate power until the field current can decrease, so much more energy can be released.
15.
Alternators used in central power stations also control the field current to regulate reactive power and to help stabilize the power system against the effects of momentary faults.
16.
While the rotating field winding consumes a fraction of a percent of the generator output, adjustment of the field current allows good control over the generator output voltage.
17.
Once the engine is running and the alternator is generating power, a diode feeds the field current from the alternator main output equalizing the voltage across the warning indicator which goes off.
18.
In a separately excited ( sepex ) motor the field coils are supplied from an independent source, such as a motor-generator and the field current is unaffected by changes in the armature current.
19.
It will run as a motor powered by the AC network, and by adjusting the field current, it can be a synchronous condensor, correcting the power factor and raising the system voltage to a desired level like a bank of capacitors.
20.
While most modern circuit breakers will interrupt the fault current in less than 50 ms, the fault current from the generator will take several seconds to interrupt because the field current in the rotor takes this amount of time to discharge.