AC Power vs. Field Current of a DC Generator: Explained

[BuckeyeNut]

I am trying to understand this curve; it is AC Power vs. Field Current of a DC Generator. I am not sure what its significance is? What it's telling me? Can someone please explain it to me? See attached image.

BTW... Pac = AC Power
If = field current
Poc = open circuit power
Prot = rotational power (I believe)

Thanks in advance!

 

[NascentOxygen]

Hi BuckeyeNut.

It helps if you provide some background to figures, but I'll take a stab. First, devise a fitting scenario...

You have an AC motor turning a self-excited DC generator. As you adjust the setting for a stronger field current you are requiring the generator to produce more current to more strongly magnetise its own stator. Generating this current requires mechanical power, and this drive comes from the prime mover.

The speed is kept constant, meaning rotational losses are fixed, so that component of the load on the prime mover is not varying, it's the increasing power needed for generating the DC for the field that causes the rising curve in the sketch.

The picture may not be of two machines, either. It might just be a self-excited synchronous generator. P_oc might be more descriptively labelled as representing the electrical power component with no external load on the generator (open-circuit terminals).

Does this fit the context from which you extracted the figure?