Good day,

Could you please explain me the phenomenon when our power plant receive a lot of MVAR (reactive power from the grid) or produce a lot of reactive power. I want to know what is the best: produce enough MVAR or receive MVAR from the external huge power plant.

Thank you and best regards,

 

Better day,

For starters, I wouldn't necessarily consider a 600 MW power plant small.

There's way too much about your plant, and it's relation to and position on the grid in your part of the world, that we don't know to be able to make a comment about the effects of VArs (leading or lagging) or your power plant.

Every synchronous generator (alternator) I've ever seen was provided with a piece of documentation called a reactive capability curve, or some similar name. It's actually three curves on one drawing, and it represents the ability of the generator to produce power, both real power (watts) and reactive power (VArs) under differing conditions, and the conditions are usually the temperature of the gas (hydrogen or air) being used to cool the generator.

Because the problem with power (real or reactive) is that when it's flowing through conductors it generates heat. More power means more heat. And, the ability to cool the generator is usually the upper limit of the generator's ability to produce power, real or reactive.

The three curves usually represent three operating limits: Lagging VARs; Real Power (Watts); and Leading VARs. Under normal conditions when lagging VARs are "flowing" in the generator, it's usually the result of a high rotor current. So, the ability to cool the generator rotor usually defines that limit.

At high watt outputs (real power), there is high current flowing in the stator windings. So, the limit on real power output (other than the ability of the prime mover to produce torque which is converted to amps by the generator) is the ability to cool the stator windings.

When lagging VArs are "flowing" in the generator then there are specific stator winding areas where heat is concentrated so the ability to cool those areas is usually the limiting factor for this condition.

Under normal operating conditions, it's not desirable to have a lot of VArs flowing in the generator, either Lagging or Leading. Under normal conditions, high Lagging VAr flows can actually reduce the real power output of the unit.

And, under normal conditions high Leading VAr flows can lead to catastrophic mechanical failures.

But, if your plant is experiencing "high" VAr flows in both the Lagging and Leading "directions" then it's likely that something is amiss with the excitation system(s) or there is something about the grid which we don't know. That's why I really hesitate to make any kind of statement about your plant, because we don't know what values of VArs your plant is experiencing, and we don't know enough about the conditions at your plant and in your part of the world.

VArs are a funny thing. People say, "They're like foam on beer: they're just "there" and they don't do anything!" And, yet, as power plant operators we are continually told to monitor the VArs (or the power factor, which is another way of measuring reactive power) but we're not told why, if they're not important, we have monitor them and control them. Reactive power is an important component of power generation (and consumption) that is just poorly understood and described.

The amount of VArs to be "produced" by any power plant is usually specified, within limits, by some regulatory agency or by the company which owns and operates the grid with which your power plant is connected. If not, then the ideal situation is to run the generator with zero VArs, since most power plants are not usually paid for the VAr-hours they "produce", only for the Watt-hours.

Be very careful of your terminology when discussing VArs here on control.com. I suggest you write to one of the posters here on control.com, Phil Corso, at cepsicon (at) aol (dot) com, and supply him with your name and the name of the company you work for, and he will send you his write-up on Armature Reaction, which is related to this topic.

That's all I can add to this thread. Take it away, Phil!

 

Good day,

Kindly check the capability curve of your generator and you can judge on this issue.

Bye

 

Thank you MR phil,

It's right.

but for your information in our power plant, we monitor only the MVAR's Exported to partner to be almost zero, and also monitor the Generator MVAR don't exceed Lagging/leading side. also line voltage should be between 110Kv and 114.4Kv, and also Generator voltage between 16.5Kv to 17Kv and that's all. so I mean that we don't monitor the MVAR's production only. we use The Generator transformer OLTC (On Load Tap Changer) to regulate all these parameters and additional comparing our plant ( 600Mw) to the Grid (around 5000MW). any tripping or fluctuation in the frequency or voltage can affect us and obligate us to run our plant in ISLAND operation (Not connected to Grid = GOV Mode). Actually we are on LL (Load Limitter Mode). Mr Phil, I think now you understand my question.

Thank you very very much and awaiting for your nice explanation
Heni

 

<b>I KNEW IT!

I KNEW YOU WERE USING TAP CHANGERS TO CONTROL VAr FLOW!</b>

You deliberately withhold relevant information and ask broad questions, in multiple threads, and reply to the wrong thread.

And then you smugly reply with a few more details, indicating you are patiently waiting for a more detailed explanation. This isn't a game.

Fool me once, shame on you.
Fool me twice, shame on me.