Power factor

[mbrooke]

this might help, a good basic description of a synchronous generator (electrical and mechanical speed are synchronized, no slip)
http://www.egr.unlv.edu/~eebag/Synchronous Generator I.pdf

it can supply or absorb VAr depending on the load
it can have a leading or lagging pf
the key is the angle between to field and the rotor

Awesome! (and thanks!) Let me digest all this and ask questions to grasp it all.

 

[mbrooke]

it can supply or absorb VAr depending on the load
it can have a leading or lagging pf

So if I add a capacitor across the output the generator would be considered to be consuming VARs, and if I added a reactor across the generator it would be considered to be supplying VARs?

Adding a capacitor would cause the voltage to rise, a lagging load would cause the voltage to dip and a resistive load would cause voltage to remain steady, hence where voltage controllers/exciter controls come in? What takes place in the generator to cause this however, something with the rotor angle in conjunction with the exciter or rotor current?

the key is the angle between to field and the rotor

Ok, so though limited my understanding is that a leading PF nudges the rotor for ward and then back ward while a lagging load nudges it backward and then forward? Or am I way off?

 

[Sahib]

where does the load stand then? ISn't PF a function of the load and the generator takes which ever?

Yes. You are correct. But consider the generator part of the grid. If you then try to increase voltage of generator, it will only change power factor of generator i.e change in reactive power output.

 

[mbrooke]

Yes. You are correct. But consider the generator part of the grid. If you then try to increase voltage of generator, it will only change power factor of generator i.e change in reactive power output.

Makes sense. So in essence the generator will simply behave as a reactor? As though shunt reactor was added to the generation buss?

 

[Besoeker]

Makes sense. So in essence the generator will simply behave as a reactor? As though shunt reactor was added to the generation buss?

It can act like a capacitor. See my post about synchronous condensers.
Or this:

http://www.energy.siemens.com/mx/en/power-transmission/facts/synchronous-condenser.htm

 

[mbrooke]

It can act like a capacitor. See my post about synchronous condensers.
Or this:

http://www.energy.siemens.com/mx/en/power-transmission/facts/synchronous-condenser.htm

But not like a reactor? Or both?

 

[Sahib]

Makes sense. So in essence the generator will simply behave as a reactor? As though shunt reactor was added to the generation buss?

More than that. If you try to increase speed of any grid connected generator, it will only increase active power output of generator.

 

[Sahib]

But not like a reactor? Or both?

A generator may not be considered that way. Because it is a supplier of energy. The reactive power required by many equipment including reactors is also supplied by generator unless locally by capacitors.

 

[mbrooke]

A generator may not be considered that way. Because it is a supplier of energy. The reactive power required by many equipment including reactors is also supplied by generator unless locally by capacitors.

Correct, but its being said a generator can also act as a capacitor (synchronous condenser)

 

[Besoeker]

Correct, but its being said a generator can also act as a capacitor (synchronous condenser)

And by a fairly reputable source at that. Or sources, come to that.

 

[GoldDigger]

Correct, but its being said a generator can also act as a capacitor (synchronous condenser)

IMHO the problem with using a generator as a source of capacitive VARs is not an inherent physical one but one of the stability of standard voltage regulation schemes under those conditions.

 

[Sahib]

Correct, but its being said a generator can also act as a capacitor (synchronous condenser)

A synchronous motor is a different beast in action from a synchronous generator.(By generator I meant synchronous generator in my post 268). The synchronous motor can act as inductor or capcitor depending on field current.

 

[mbrooke]

A synchronous motor is a different beast in action from a synchronous generator.(By generator I meant synchronous generator in my post 268). The synchronous motor can act as inductor or capcitor depending on field current.

How is the field current varied to mimic a cap or reactor?

 

[mbrooke]

And by a fairly reputable source at that. Or sources, come to that.

I know But the concept is well over my head >>> :dunce:

 

[Besoeker]

I know But the concept is well over my head >>> :dunce:

Don't denigrate yourself!
You don't have to know how it works, just that it does.

 

[Bugman1400]

How is the field current varied to mimic a cap or reactor?

The field voltage is decreased to under-excite the field and act like a reactor that absorbs VARs. The field voltage is increased to over-excite the field and act like a capacitor to produce VARs.

 

[mbrooke]

Don't denigrate yourself!
You don't have to know how it works, just that it does.

You know thats not how I roll!

 

[mbrooke]

The field voltage is decreased to under-excite the field and act like a reactor that absorbs VARs. The field voltage is increased to over-excite the field and act like a capacitor to produce VARs.

Starting to make sense. Does the rotor speed up or slow down during each half cycle or all the energy is sent/returned without having that effect?

 

[Ingenieur]

I know But the concept is well over my head >>> :dunce:

understand it conceptually, not mathematically
basically electric (caps leading) and magnetic (induct lagging) fields rising/collapsing in an oscillating manner between source/sink
basically required to 'charge' the system, perform no real work, but still must be supplied

 

[Ingenieur]

Starting to make sense. Does the rotor speed up or slow down during each half cycle or all the energy is sent/returned without having that effect?

the rotor speed is constant, synched to the frequency or the prime mover
the rotor and the field relationship varies based on load/pf

in a away, not unlike a DC motor (except field rotates, not commutated)
rotor is the field, DC from a rotor mounted gen/bridge or an external source
the stator is the armature, flux from the field induces a current and EMF since it is moving in relation to it