Power factor

Status
Not open for further replies.
Ingenieur said:
it can supply or absorb VAr depending on the load
it can have a leading or lagging pf
Click to expand...


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
Click to expand...


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?
 
mbrooke said:
where does the load stand then? ISn't PF a function of the load and the generator takes which ever?
Click to expand...
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.
 
Sahib said:
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.
Click to expand...

Makes sense. So in essence the generator will simply behave as a reactor? As though shunt reactor was added to the generation buss?
 
mbrooke said:
Makes sense. So in essence the generator will simply behave as a reactor? As though shunt reactor was added to the generation buss?
Click to expand...
More than that. If you try to increase speed of any grid connected generator, it will only increase active power output of generator.
 
mbrooke said:
But not like a reactor? Or both?
Click to expand...
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.
 
Sahib said:
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.
Click to expand...

Correct, but its being said a generator can also act as a capacitor (synchronous condenser)
 
mbrooke said:
Correct, but its being said a generator can also act as a capacitor (synchronous condenser)
Click to expand...

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.
 
mbrooke said:
Correct, but its being said a generator can also act as a capacitor (synchronous condenser)
Click to expand...
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.
 
Sahib said:
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.
Click to expand...

How is the field current varied to mimic a cap or reactor?
 
Bugman1400 said:
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.
Click to expand...

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?
 
mbrooke said:
I know :) But the concept is well over my head >>> :dunce:
Click to expand...

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
 
mbrooke said:
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?
Click to expand...

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
 
Last edited:
Status
Not open for further replies.
Top