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relation b/w mechanical i/p, turbine speed & load variation

relation b/w mechanical i/p, turbine speed & load variation

relation b/w mechanical i/p, turbine speed & load variation

(OP)
Turbine speed remains constant at rated speed once the m/c is synchronised....during change in load the governer issues command for opening/closing of nozzle/deflector which means mech. i/p (water/steam)to the turbine is varied accordingly.....however the turbine speed has to remain at rated speed despite the mech. i/p....the question is how does the load(power o/p) vary at constant rated speed???  

RE: relation b/w mechanical i/p, turbine speed & load variation

Hello - and welcome. You seem to be a new face in here.

To answer your question: There's more to power than speed alone. There's also torque. When the load increases, the mechanical input to the turbine increases to add more torque.

If you look at the attached generator, you will see a change - not in speed, but in pole angle - and in current, of course.

Power = rotational speed times torque. If rotational speed is constant and power increases, the only factor that can change is the torque. And that is exactly what happens.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: relation b/w mechanical i/p, turbine speed & load variation

(OP)
thx skogsg...but could u elaborate theoritically on how the turbine speed is maintained const. while mech. i/p is more.?
if it is for the governer then how does it regulate...wat i'm confused abt is dat "if we increase the mech i/p then turbine speed will increase & if governer is to take action in maintaining a const. speed it has to ultimately control the mech i/p which means it has to reduce the i/p agn." i hope u understand wat m' tryin to say... hey mind not coz m' very new to this subject n, dont hav mch idea...it would b nice of u to guide meh.... thx

RE: relation b/w mechanical i/p, turbine speed & load variation

Do you chat via your telephone? Or do you have a full keyboard available?

If you are sitting at a computer, I would appreciate if you rephrase your question. And, please, use capital letters, punctuation and no abbreviations. That is how we communicate here.

Also, please redflag your redundant thread with my handle. All you wanted to say is probably included in this thread.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: relation b/w mechanical i/p, turbine speed & load variation

After sync the generator is locked to the grid and the grid maintains the speed. The governor responds to speed changes and there should be no speed changes when sync'ed to the grid. The governor may be placed in droop mode and then used to set power supplied to the prime mover. A smaller machine on the grid will usually be running at a fixed power output and the governor does not control except to set the throttle opening and to prevent a runaway in the event of a load loss.
PS
Hi kixs84;
Skogs speaks several languages fluently including Boolean.
However I don't think that he is fluent in tx. We do our best to overcome the language barriers inherent in an international forum but not many of us older members are NOT comfortable communicating in tx. Can you repost in English with capitalization?
thx

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: relation b/w mechanical i/p, turbine speed & load variation

thx bill, u r gd frnd - cn ustnd w kx sez - jst wntd btr lng in here

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: relation b/w mechanical i/p, turbine speed & load variation

Skogs;
Do you have multiple loose connections in your keyboard?
LOL
I don't have many brain cells left. When the few synapse connections that I have left are struggling to decipher tx, I have little capacity left for the problem at hand.

Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: relation b/w mechanical i/p, turbine speed & load variation

kixs84;
Try a search of this site. There are many discussions and explanations of governor action.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: relation b/w mechanical i/p, turbine speed & load variation

Bill and Gunnar,

You guys are better lads than I am.  About half way through his second post, I gave up and said what the he**.  If he/she isn't interested enough to make the question comprehensible, I don't have the time or patience to try to decipher it, even though I did know the answer.

Want to bet this thread will be gone in the morning?

rmw

RE: relation b/w mechanical i/p, turbine speed & load variation

I wouldn't mind - really.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: relation b/w mechanical i/p, turbine speed & load variation

(OP)
Hi Skogsgurra & waross,
well my doubt is, how does the turbine speed remain constant despite increase in mechanical input.
now for your understanding take an example:-
The machine is connected to the grid and i am trying to increase the station load. Now when i issue command for increasing the load, what actually happens is mechanical input(water/steam) to the turbine is increased. So , in this case more force is exerted on the turbine (which is already at rated speed) and  will tend to increase the rotational speed.
However, the machine remains at rated speed. now how does this speed remain constant.
    

RE: relation b/w mechanical i/p, turbine speed & load variation

Much better, kix!

There are two main types of generators for alternating current. The synchronous and the asynchronous generator. The synchronous generator has a rotor with magnetic poles that are locked to the grid frequency. It simply cannot move faster (or slower) without tripping.

The other type is asynchronous. That one runs slightly overspeed - and more so the more power the turbine puts into it. The difference between 'grid speed' and generator speed is called slip and is usually in the 1 - 3 percent range.

All large power plant generators are of the synchronous type. Their speed is constant and all that happens when turbine 'pushes harder' is that he pole angle (angle between stator flux and rotor poles) increases.

Smaller plants often use the asynchronous generator. For that type of generator, your assumption about constant speed is not valid. It adapts speed after load.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: relation b/w mechanical i/p, turbine speed & load variation

(OP)
Thx a lot skogsgurra!
so what i understand now is that the change in speed is compensated by change in pole angle which ultimately results in the change in load/power.
now in this regard can you state some relations describing the realation between speed,torque, power and load angle so that i can have a clear understanding.
thx agn.

RE: relation b/w mechanical i/p, turbine speed & load variation

"so what i understand now is that the change in speed is compensated by...."
In a synchronous machine connected to the grids there is no change in speed.
Somewhere on the grid there are one or more large machines that compensate for load changes and variations in distributed generation inputs to keep the frequency and resulting speed constant.
Think of one bell crank driving another by an elastic band between them. One crank is held at a constant speed (by the grid). The force driving the input crank is increased. (Throttle or steam valve opened further.) The elastic bank stretches a little and the angle between the driving and driven cranks increases slightly. In a synchronous alternator the rotor is feeding power to the grid by pulling against a rotating magnetic field. As more power is applied, the rotor pushes harder. The magnetic field distorts and stretches slightly and the angle changes slightly.
If you were to make an index mark to show the position of a generator rotor in relation to the stator you may be able to observe the shift with a strobe light. Triggering the strobe light at the correct time is a solvable problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: relation b/w mechanical i/p, turbine speed & load variation

In a synchronous motor/generator, the torque on the rotor is proportional to the sine of the angle between the magnetic fields of the rotor and stator -- think of the rotor as a glorified compass needle. In reasonable zones of operation, this is close to being proportional to the angle itself. So as waross points out, the effect is analogous to that of a spring or elastic band.

If you want to analyze this more formally, the angle will be proportional to the arcsin of the torque, and at constant speed, to the power.

Curt Wilson
Delta Tau Data Systems

RE: relation b/w mechanical i/p, turbine speed & load variation

Kix,

Think of it this way.  In the explanations given above, the assumption was that the generator in question didn't have the ability to overpower the grid and speed it up (increase its frequency) - massive grid, small generator by comparison.  Now, assume that the generator is more massive than the grid (small islanded system, large generator).  I this case, if you add enough torque via the driver, you can increase the speed (frequency) of the grid and you can increase it until you run out of the driver's ability to add torque.  Islanded generators, however run on a different control scheme than generators hooked to a large grid.  Those here more skilled than I will have to explain that.

rmw

RE: relation b/w mechanical i/p, turbine speed & load variation

Several islanded governors often run in droop mode or proportional band plus offset.
One of several paralleled generators may be in isochronous mode with the others in droop mode..
A single islanded set may run in droop mode or isochronous mode.
Droop mode is very similar to proportional control plus offset with about 3% proportional band.
Isochronous is similar to proportional plus offset plus reset, or proportional plus offset plus integral. PI of a PID controller.
If you are not familiar with these control terms, try searching this site. Search also for "governors".

Bill
--------------------
"Why not the best?"
Jimmy Carter

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