throw some light how actually mechanical energy or say heat energy converted into electrical energy in a thermal powerplant. and what exactly is AVR and synchronization of generator

 

Generators are devices for converting mechanical energy (in the form of torque applied to the generator rotor) into electrical energy. (Electric motors are devices for converting electrical energy into torque to be used to perform mechanical work.)

In a thermal power plant heat is produced (usually through the combustion of some form of liquid or gaseous hydrocarbon-based fuel) and that heat is converted to mechanical energy (torque) by an engine of some sort--a reciprocating engine, or a turbine (combustion turbine or steam turbine). The device that produces the mechanical energy from a source of heat (steam or burning hydrocarbon-based fuel) is called the prime mover of a generator. The prime mover and the generator are coupled together, sometimes directly, sometimes through a gearbox assembly. The prime mover spins the generator rotor by applying torque to the generator rotor. And, again, the job of the generator is to convert that mechanical energy (torque) into electrical energy (watts, kW, MW).

In order for the generator to produce electrical energy there must be two distinct magnetic fields inside the generator. The rotor of a synchronous generator is a very large electromagnet that can have a variable (adjustable) direct electric current/voltage (DC) applied to it. The AVR (Automatic Voltage Regulator) is the device that is used to control and adjust the amount of DC current/voltage applied to the synchronous generator rotor. A stable generator terminal (output) voltage requires a stable generator rotor magnetic field which is the result of a stable AVR output. Stable generator terminal voltage (generator output voltage) is important for a stable electric power transmission and distribution grid/system. As a general rule, generator terminal voltage (output voltage) doesn't vary much more or less than 5% of the nameplate rating of the generator (for many synchronous generators the generator terminal voltage is 11,000 Volts (11 kV) or 13.8 kV. 5% of 11 KV is 550 Volts; 5% of 1.38 kV is 690 Volts; it's important to note that generator terminal voltage (output voltage) doesn't change much at all when the generator is producing electrical energy, it's actually relatively constant and doesn't usually change by more than 5% of rated, if that much.

The other magnetic field is produced by stator (stationary) windings of the generator which will have an alternating current/voltage (AC) flowing through the windings. The frequency of the AC current/voltage in the stator windings of a synchronous generator that IS NOT connected to (synchronized with) a grid or distribution system made up of many other generators and their prime movers is a function of the rotational speed (RPM, Revolutions Per Minute) of the synchronous generator's rotor. And, the prime mover (reciprocating engine or turbine (combustion or steam)) is the source of the speed of the rotation of the generator's rotor. So, to produce a stable frequency (50 Hz or 60 Hz) it is necessary for the prime mover to rotate the generator rotor at stable speed. A stable frequency is very important for a stable grid. Very important.

The electrical power produced by a synchronous generator (which is being driven by its prime mover) is calculated by multiplying the output voltage of the generator (the generator terminal voltage--the voltage of the stator (stationary) windings) times the amperes flowing in the stator windings. This product is then multiplied by the square root of three (for three-phase synchronous generators) and this product is multiplied by something called the power factor of the generator output (a number which is never greater than 1.0 and, generally, represents the "efficiency" of the generator's conversion of mechanical energy to electrical energy). In a formula it looks like this:

Power (Watts) = Vt*Ia*1.732*pf

where Vt is Generator Terminal Voltage (generator output voltage)
Ia is Generator Armature (Stator) Current
pf is Generator Power Factor

It was already said that the generator terminal voltage of a synchronous generator producing electrical energy (power) is relatively constant and doesn't change by more than approximately 5% of the nameplate rating of the generator. And, 1.732 (the approximate value of the square root of three) is a fixed value--it NEVER changes. And for the purposes of this general discussion we are going to assume that the power factor of a generator is 1.0, which is also a fixed value. So, three of the components of the formula for calculating electric power are basically fixed (unchanging) values (the generator terminal voltage can vary a little, and the power factor can vary somewhat--but under normal operating conditions they are usually stable and can be considered to be fixed (not changing)). So, if three of the four components of the electric power formula are fixed (don't change very much, if at all) then if one wants to increase the amount of electrical power produced by a synchronous generator one has to increase the amperes (Ia, the stator amperes) of the generator. And stator amperes are directly proportional to the amount of torque being applied to the generator's rotor by the prime mover coupled to the generator rotor. It's as simple as that: increase the mechanical energy (torque) being applied to the synchronous generator's rotor and the power (Watts; kW; MW) will increase. One doesn't change the electrical power being produced by a synchronous generator by changing the generator terminal voltage (Vt), and even if one wanted to do that the net effect of changing the generator terminal voltage will have less than a 5% impact on the amount of power (Watts; kW; MW) being produced by the generator. One can't change the suare root of three--it's a fixed value all day, every day, every week, every month, every year, every decade, every century. And, to finish this section of the description of a thermal power plant's basics suffice it to say that the power factor (pf) of a synchronous generator is never usually less than 0.8 and can't ever be more than 1.0--and for all practical purposes one doesn't change the power output of a synchronous generator by adjusting a generator's power factor (which is done by adjusting the AVR output).

The critical takeaways you need to have and always remember about AC (Alternating Current) power generator, transmission and distribution systems are this:

1) The frequency of a grid is extremely important.
2) The amount of electrical power (Watts; kW; MW) produced by a synchronous generator is a function of the amount of amperes flowing in the generator's stator windings.
3) The amount of amperes flowing in a synchronous generator's stator windings is a function of the amount of torque (mechanical energy) being applied to the generator's rotor.
4) EVERY synchronous generator and prime mover connected to a grid with other synchronous generators and their prime movers operates at the SAME frequency as every other generator on the grid (it's IMPOSSIBLE to have one generator running at 48.76 Hz and another running at 52.31 Hz, and another running at 50.45 Hz and another running at 50.09 Hz--they ALL run at the SAME frequency as the grid they are connected to). Full stop. Period.
5) Synchronous generator frequency and generator rotor speed are directly related (proportional)--which means that every generator connected to a grid is spinning at a constant speed (if the grid frequency is constant).

Synchronizing a synchronous generator to a grid with other synchronous generators is the act process of adjusting the incoming generator's frequency (speed--since frequency and speed are directly related) and terminal voltage to be very nearly equal to the grid's frequency and voltage and then closing the generator breaker at an appropriate time. Failing to do so can can very serious and catastrophic damage to a generator and its prime mover. Synchronization can be done manually (by a trained and knowledgeable human being) or automatically (by a properly configured automated control system device--which has to send signals to the prime mover's control system (often called a governor) AND the synchronous generator's AVR).

Is that enough light for you?

 

Thank you, being a mechanical engineer, it's bit difficult to understand at one go. But got some idea.it would be helpful if u share any material.

 

There are SO many YouTube videos and lots of written materials with drawings and such. I can barely draw with a pencil and eraser on paper, and my computer drawings skills, ..., well, let's not talk about them.

There has been lots written on Control.com about synchronization, and prime movers and generators.

Since you're mechanically inclined think of a generator and motor like a hydraulic pump and hydraulic ram or hydraulic ram or hydraulic transmission. The hydraulic pump creates pressure and provides flow at pressure; the "end" devices (hydraulic rams or hydraulic motors or hydraulic transmissions) convert the pressure and flow to useful work. The hydraulic fluid is a medium to transmit work from one place to another with hydraulic tubes and pipes and hoses to another place where it can be converted back into work again.

Electricity is exactly the same. A generator converts mechanical energy it derives from its prime mover into electricity which is then transmitted and distributed to many places where motors (and other "electric" devices that perform work) convert the electricity back into useful work. That's all electricity is--a medium for transmitting energy from one place to another--over wires in this case.

AND, it's ALL ABOUT magnets and magnetic fields (at both ends, the generators and the electric motors). Simple magnetism. With a lot of fancy mathematics and formulas and calculations that just confuse a LOT of people instead of helping to understand them.

Think about how two magnets attract each other (the opposite poles attract each other). And how much they repel each other when you try to push like poles together (North repels North; South repels South). It takes a LOT of force to push the like poles of two magnets together--even small magnets. And sometimes it's even difficult to pull two magnets apart when the opposite poles are attracted to each other.

When a synchronous generator (and its primer mover) is being synchronized to a grid with other generators (and their prime movers) if the process isn't performed correctly then what can happen inside the incoming generator is that the poles of the two magnetic fields inside the generator can be misaligned--and that can cause hellacious mechanical forces on the generator rotor--which can affect the coupling or gear box between the generator and the prime mover and the prime mover, also. Synchronization is critical when connecting a generator and its prime mover to a system with other generators and their prime movers.

When a generator output is increased what initially happens is that the prime mover tries to increase the speed of the generator--but because it's connected to a grid with other generators (and their prime movers) it is LOCKED into a speed that is proportional to the frequency of the grid and it CAN'T go any faster. But, there is a twist that occurs between the prime mover and the generator and when the prime mover output is increased the coupling and generator rotor get twisted just a little more and that is actually trying to break the magnetic attraction between unlike poles apart. The AVR is an important part of maintaining the alignment of the magnetic fields inside the synchronous generator.

So, as a mechanical person you're thinking, "He's saying that increasing the fuel or steam flowing into the generator prime mover doesn't increase the speed of the generator--but during starting and acceleration to rated speed [which is the speed that corresponds to the grid/system frequency] increasing the fuel or steam flow increases the speed. Something doesn't seem right. When I press on the accelerator pedal in my automobile or twist the throttle of the motorcycle I ride the speed of the vehicle increases." There are no magnetic forces at work which are limiting the speed of the automobile or the motorcycle when you press on the accelerator or twist the throttle. BUT, there are great magnetic forces at work inside the generator keeping the speed of the generator rotor locked into the speed that's a function of the grid frequency so that extra torque that would cause the speed of the machine to increase gets converted by the generator into more amperes flowing in the generator stator windings--which cause the Ia component of the power formula to increase which increase the watts/kW/MW.

Again, if you want drawings and diagrams there are any number of them available on the World Wide Web and YouTube. I just have one caution for you: MANY textbooks and reference materials will say that when you increase the load on a generator and its prime mover that the speed of the machine (the generator and its prime mover) will slow down. And, that's only true in a certain scenario--which almost never happens in real life. It's all the egghead professors and ivory tower author types who write these books but have little or no real world experience and who FAIL to explain all of the circumstances of how what they are describing would happen that cause a very great deal of confusion and doubt. If the number of motors and lights and computers and computer monitors and tea kettles and televisions increased on the grid system (which means the "load" being carried by the grid/system has increased) BUT nothing was done to increase the energy flow-rate (steam or fuel) into the generator prime mover(s), then yes, the amount of power being produced by the grid/system and being consumed by the loads connected to the grid/system will increase AND the frequency (speed) of the entire grid system would slow down. (Usually when these textbooks and references are talking about speed and load and frequency they are referring to a single generator with a governor that isn't trying to maintain speed/frequency--but they NEVER say that. Because, that just doesn't happen in the real world, especially for one prime mover and generator because the prime mover governor tries NOT to let that speed change, sometimes it tries harder than others, but it doesn't want to see the speed change. (All of this is described in detail in the discussions on Control.com about Droop Speed Control and Isochronous Speed Control.)

I want you to think about a grid/system where multiple generators and their prime movers are connected together--they are sychronized together!--as a single generator and prime mover. Because, in essence, that's what they all are. And that's another way to come to grips with the fact that when synchronized together all generators and their prime movers spin at speeds that correspond directly the frequency of the grid. Not one single generator and prime mover can have a frequency more or less than the frequency of the grid--or you wouldn't get 50 Hz or 60 Hz out of the receptacle on the wall. They all have to be operating at the same frequency--which means speeds directly proportional to the frequency of the grid. It just must be.

And it's magnetism that's keeping all of this synchronized together.

Connecting multiple generators (and their prime movers) together (often called paralleling, or parallel operation) means the system can supply/power loads larger than any single generator and its prime mover. Because when paralleled (synchronized) together they are all acting as one very large generator and prime mover. Operating at a single frequency.

That's it. That's me. I'm done.

If you can grasp these concepts and internalize them you will know so much more than even most power plant operators, most supervisors and some power plant managers. (Yep; you read that right.) And, as a mechanical person working in a thermal power plant this is all you really need to know--but you need to know and understand the basics. Generators convert torque into amperes, which can be transmitted using wires to remote locations so motors (and other electrical end devices) can convert the amperes back into torque or other useful purposes. As you grow in your job and duties and responsibilities you need (if you don't already know how) to be able to read and understand P&IDs (Piping and Instrumentation Diagrams) because they are the "schematic" drawings of the various systems in the plant and as a mechanical person you need to know how different components of systems all work together to perform their tasks in the plant so you can determine of something is working correctly or not and then fix it. (Power plant operators need to know this too--but, most don't, or they have a rudimentary understanding or a very poor idea of systems and operations. They just think they need to know who to call when an alarm is annunciated....)

Later!