Generator Synchronisation

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Thread Starter

Mohan12111990

I have read the content regarding how generator synced with grid and floating and all...
My question is...as mentioned torque is converted into amps...can anyone please explain how? and rpm doesn't change when at full load and floating?

I m working in 12*3mw hydro power house. we have three synchronous generator, pelton turbine. I couldn't understand the fact that once generator is synced with grid, rpm doesn't change which stays same when floating and also subjected to full load. but at full load with same rpm, we get 12 mw per machine.

as I've got answer that torque is converted to amps. can anyone pls explain how torque is converted to amps and why speed doesn't raise...

my mail ID is mohan.nov1990@gmail. com....
 
Mohan12111990

Can we agree that motors convert electric current into
torque--motors drive pumps and compressors and elevators and
conveyors and such. (By the way, the largest use for
electric power is pumping water--fresh water; grey water;
sewage water; etc.)--and electric motors drive those pumps.

And, can we agree that generators drive motors? And that
current is what varies between generators and motors
(electric voltages vary--but that's done via transformers
and to reduce losses during transmission and distribution)?
The formula for three-phase electric power is:<pre>P = Vt *
Ia * (3^0.5) * pf

where P = Power (Watts)
Vt = Generator Terminal Voltage
Ia = Generator Armature (Stator) Current
pf = Power Factor</pre>Under normal operating
conditions, generator terminal voltage remains relatively
constant. The square root of three is a constant. And,
presuming the power factor remains relatively constant (it
should stay pretty close to 1.0, and not much less than 0.8
positive or negative), the only variable in the equation is
armature (stator) current.

And prime movers drive generators--hydro turbines in your
case. The only quantity the hydro turbine can produce is
torque, which is directly applied to the generator which the
generator then converts into amperes in the generator
stator, which are distributed to motors (loads) via wires,
which motors re-convert into torque.

Nobody ever seems to have a problem with the fact that
motors convert torque into amperes--but EVERYbody seems to
have a problem with generators converting torque into
amperes. Torque is the only parameter applied by prime
movers to generators. And, everyone agrees that generators
are needed to drive motors.

If you want the maths and physics and vectors and load
angles and such for how that is all
<b><i>proven</b></i>--you can find it all over the World
Wide Web with your preferred World Wide Web browser. All of
the maths and formulas and vectors and load angles just
prove what is happening inside the generator--that's all. If
maths and formulas and vectors and load angles and back-emfs
and armature reactions help you to understand all of
that--there are hundreds, probably thousands, of World Wide
Web sites and YouTube videos to peruse and study. We can't
put graphics or drawings in our responses on
control.com--but we shouldn't have to, because it's all
readily available in lots of different forms and
explanations on other World Wide Web sites.

As for why speed doesn't change--that's because there are
very great magnetic forces at work inside the generator. Two
of them: one a result of the DC current applied to the
generator rotor (the "field") and one a result of the
current flowing in the armature (stator) when supplying a
load or loads. You know what happens when you try to
separate two magnets with their North and South poles
touching each other. And, you know what happens when you try
to force the North poles of two magnets to touch each other.
Well, that's exactly what happens in a synchronous
generator. And the North pole of the generator rotor is
locked into step with the apparently rotating South pole of
the generator armature, and the South pole of the generator
rotor is locked into step with the apparently rotating North
pole of the generator stator. And, the prime mover is trying
to separate the poles--but the magnetic attraction is SO
strong they can't be separated.

That's another thing for which there are thousands of
articles and videos about on the World Wide Web--how AC
motors and AC generators (specifically synchronous
generators) work. How the alternating current flowing in the
armature (stator) of both motors and generators induces a
magnetic field that appears to rotate around the stator. And
that magnetic field captures the opposite poles of the
generator rotor's magnetic field and keeps it locked in
<b>synchronism</b> with the speed of the apparently rotating
stator magnetic field.

Again, this is the place to start: Agreeing that motors
convert torque to amps. And generators convert amps to
torque. The prime movers driving the generators are actually
doing the work of the motors connected to the
generators--the prime mover torque is transmitted from where
it is produced to motors (and other loads) where torque is needed,
and is useful, by converting it to amperes (in the generator)
and then converting it back into torque in the motors.

And, the basic physical principles of AC synchronous
generators and AC electric motors rely on magnetism--it's
all about magnetism. And we all know how magnets work and
attract and repel each other.

So, if we can't agree on this and start here--and then you
can find the proofs (used by machine designers to build
machines and predict their power input/output) to help with
your understanding, then, well, there's not much more to be
done. It's not rocket science--obviously--it was developed
before rockets started being used to put objects into
space/orbit. It's very basic, and it all starts with
magnetism. Electricity is the way for
transmitting torque (power) from a place where it is
plentiful or can be produced (think hydro turbines!) to
places where is can be useful or is needed (think homes and
businesses and factories located long distances from the
water used to power the hydro turbines which drive the
generators). The hydro turbines are actually doing the work
of all the loads at the other end of the wires connected to
the hydro turbine's generators.

We gotta start somewhere--and let's get this all sorted
before we start directing you to maths and formulas and
vectors and load angles and emfs and back emfs and
counter-emfs and armature reactions--all of which are just
proofs of what's happening to be used to design machines and
apply them. So, ask for clarifications now--before we get
into the numbers and angles--most of which can't ever be
visualized or measured on running generators and motors.
They're intangible to the operator--no one can measure back
emf or load angle--they're just calculated values used to
prove what's happening, because man needs to have formulas
and proofs of what he sees happening in order to feel in
control of his environment.

All of which is really interesting when you consider that we
(thinking men) don't know what electricity is. That's
right--we don't know if electricity is a mass with a charge,
or a charge with a mass. But, we do know how to use it, and
we do know how to quantify it and produce it and how to
predict what will happen and build machines to use it--<b>to
transmit torque from an area where it is plentiful to areas
where it is useful or necessary.</b> Your hydro turbine
plant is probably located some distance away from houses and
factories and businesses, but there is head (water
pressure/flow) available at the place where the hydro
turbine-generators are located, and they can be easily
connected using wires to loads (electric motors and lights
and computers and computer monitors) where the homes and
businesses and factories are located.

Maths and vectors and formulas and load angles and emf and emf-this and -that and -that and air gap and all of that stuff are ways to prove that in the same way motors convert amperes into torque, generators convert torque into amperes. Electricity is just a way to transmit torque from one place to another. The hydro turbines--instead of driving generators--could be supplying torque to very long shafts with very many pulleys and belts connected pumps and fans and compressors and other devices requiring toque to the hydro turbines. But generators and wires are a much easier way to do this.

Hope this helps. If you can't understand that electric motors (which convert amperes into torque) are driven by generators (that convert torque into amperes), well, then I don't really think maths and formulas and vectors and load angles and emf-this and -that and -that is going to help you understand either. But, hey--it takes something different to help everyone to grasp new things.
 
www.wikipedia.org is a great resource for information on how things work. I'm going to quote a couple of articles from this really good website; the first is from 'Electric motor:

"An electric motor is an electrical machine that converts electrical energy into mechanical energy. The reverse of this would be the conversion of mechanical energy into electrical energy and is done by an electric generator."

The second is from 'Alternator' (which is the proper name for an AC synchronous generator):

"An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current."

The third is from 'Synchronous motor' (curiously enough):

Synchronous motors fall under the more general category of synchronous machines which also includes the synchronous generator. Generator action will be observed if the field poles are "driven ahead of the resultant air-gap flux by the forward motion of the prime mover". Motor action will be observed if the field poles are "dragged behind the resultant air-gap flux by the retarding torque of a shaft load".

This is what (electric) generators and (electric) motors do: They convert electrical energy (amperes) into mechanical energy (torque), or convert mechanical energy (torque) into electrical energy (amperes). It's as simple as that. That's all I was trying to say above.

Some of the wikipedia articles have great animations of apparently spinning magnetic fields attracting (and locking into synchronism) spinning machine rotors. There are probably hundreds, if not thousands, on the World Wide Web.

I would like to see an air-gap flux meter installed on a synchronous machine operating in a production facility. Or, an emf meter, or a counter-emf meter, or a load-angle meter. These are all things which can only be measured in a laboratory setting, and are all designed into the machine--to determine how to produce amperes or torque. They're not measured in real life, they're just ways to prove what happens with electrical machines and to design machines and to troubleshoot them. But not to operate them.

One has to remember that the first uses of electricity for revenue (money) were for motors for factories. Lights and other uses came later--it was the factories that needed torque, and prior to electricity they usually had to produce it themselves from water wheels or other mechanical methods. Force had to be used to produce torque--and by running water through a hydro turbine to produce torque, and then converting that torque into amperes the force of the water turning the hydro turbine can be transmitted long distances to motors where the amperes will be converted back into torque to produce force(s) which can be utilized in the manufacture of things to sell for money.

I don't know how to say it any differently than I--or wikipedia. And, without being able to refer the original poster to any meters or other instruments on his hydro turbine-generators to use to understand or explain what it is electric generators (and the motors they drive) do, I'm at a loss to continue.
 
Mohan12111990,

As for why the speed doesn't change when the unit is <b>synchronized</b> and the torque being applied to the generator from the Pelton turbines at your site, the answer is in the word "synchronization." When generators (and their prime movers) are connected to each other on a grid they are said to be "synchronized." On an AC power transmission and distribution system (a grid) <b>NO</b> generator and its prime mover can run faster or slower than the speed which is proportional to the grid frequency. The formula that defines that speed is:<pre>N = (120*F)/P

where N = Speed (in RPM)
F = Frequency (in Hz)
P = Number of Poles of the synchronous generator's rotor</pre>
All generators and their prime movers (most synchronous generators are directly coupled to the generators, some through reduction gears, but the speed of the prime mover is either the same as that of the generator, or is proportional to the speed of the generator) <b>MUST</b> operate at the same frequency (speed)--one generator can't operate at 50.73 Hz, another at 49.67 Hz, another at 50.02 Hz, another at 49.92 Hz, and so on. If that were possible, then it wouldn't be necessary to go through the whole process of synchronizing a generator to a grid with other generators--if the generator being connected to a grid could operate at any speed regardless of the grid frequency the process of closing the generator breaker wouldn't be so complicated (speed/frequency matching in particular; voltage matching, also). Because all generators must run at their "synchronous speed" there is a specific process required to make sure the generator is at or very near the frequency of the grid with which it is being connected ("synchronized to").

When the generator breaker is closed, current is flowing in the generator armature (stator) windings. That current develops a magnetic field (or fields) that "appears" to rotate around the stator. The magnetic forces of attraction between the generator rotor field poles and the apparently rotating armature (stator) poles keep the generator rotor spinning at a speed that is proportional to the
frequency per the formula above. (AC electric motors (those not driven by variable speed drives) also rotate at speeds proportional to the grid frequency and the number of poles of the motor rotor. The same formula applies to them, also.)

I think the "floating" operation you are referring to is sometimes called "part load" operation. And, even when the water flow through the Pelton turbines is at maximum the generator can't rotate any faster than the speed proportional to the grid frequency per the formula above. And if the Pelton turbine is coupled to the generator, it's speed will be fixed by the generator rotor's speed which is fixed the grid frequency.

Yes; when the generator breaker is open if the water flow through the Pelton turbine is increased the speed of the generator will increase because the torque developed by the Pelton turbine and applied to the generator increases. But when the generator breaker is closed the speed of the generator breaker is fixed--and the "extra" torque developed by the Pelton turbine as the flow through the turbine is increased can't increase the generator speed, and the generator converts that torque (mechanical energy) to amperes (electrical energy).

Hope this helps!
 
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