Controlling Reactive Power of a Synchronous Generator Operating in Parallel with the Grid


Thread Starter


Reading Electric Machinery Fundamentals- Chapman

It explains how the field current in the generator controls the reactive power supplied by the generator to the system.

I understand everything in the explanation except this:

The book considers the real power of the generator to be constant. Meaning that, changing de field current does not affect the Real Power supplied.

So here is my question:

How changing the field current of the generator doesn't affect the real power?

This is driving me crazy !

First, because the torque induced is proportional to the magnetic field of the rotor, and since we are increasing it. The power also increases: Pconv = Tind * w.

I can see how the reactive power changes with the field current, but I believe there is also a variation in the real power. Because when I draw the phasor diagram, increasing If changes |Ea|, and since Power supplied is proportional to Ea * sin(delta), I can't see how the real power is unaffected.

If you send your email address and tell something about yourself (student; technician; etc.) and your question to:

[email protected]

Mr. Phil Corso, who is the owner of the above email address, will be more than happy to help you with your query.

For my part, I haven't seen Chapman (the book) for twenty years, and have forgotten most of what was in it. I think you may be confusing counter-torque and applied mechanical torque?

But, contact Mr. Phil Corso off-line for detailed information--his off-line replies are really good.