Induction Genarator Frequency Control - Wind Turbine
Induction Genarator Frequency Control - Wind Turbine
(OP)
Hi!
I would be grateful if someone can explain how is voltage frequency controlled (kept constant) in the squirrel cage induction generator driven through the gearbox by the turbine connected directly to the grid. I read that generated voltage and frequency are controlled by the grid, but I don't know how. I posted a picture for better understanding. Pic: http://files.engineering.com/getfile.aspx?folder=d...
Thanks in advance!
I would be grateful if someone can explain how is voltage frequency controlled (kept constant) in the squirrel cage induction generator driven through the gearbox by the turbine connected directly to the grid. I read that generated voltage and frequency are controlled by the grid, but I don't know how. I posted a picture for better understanding. Pic: http://files.engineering.com/getfile.aspx?folder=d...
Thanks in advance!





RE: Induction Genarator Frequency Control - Wind Turbine
Reactive power will flow from the grid into the induction generator to provide magnetizing current. With any generator, induction or synchronous, where the grid is large in relation to the generator, the grid controls the voltage. A voltage difference between the generator and the grid results in a flow of reactive current.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Induction Genarator Frequency Control - Wind Turbine
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RE: Induction Genarator Frequency Control - Wind Turbine
RE: Induction Genarator Frequency Control - Wind Turbine
Exactly. The amount of torque applied to the rotor determines amount of real power the generator feeds to the grid. If no torque is applied to rotor, the generator is motored and consumes power.
RE: Induction Genarator Frequency Control - Wind Turbine
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Induction Genarator Frequency Control - Wind Turbine
With a synchronous generator/motor, the power transfer is a function of the angle difference between the grid and the rotor mechanics. In the normal operating range, it is close to a linear function, with the power transfer passing through zero as the angle difference passes through zero. (It is actually a sinusoidal function of the angle difference, which at small angles can be approximated as linear.)
RE: Induction Genarator Frequency Control - Wind Turbine
What is the purpose of the gearbox between a turbine and a generator if stator magnetic field opposes rotot motion? Isn't generator supposed to control turbine speed with stator magnetic field? Why do we need gearbox then?
RE: Induction Genarator Frequency Control - Wind Turbine
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Induction Genarator Frequency Control - Wind Turbine
Keith Cress
kcress - http://www.flaminsystems.com
RE: Induction Genarator Frequency Control - Wind Turbine
Turbine nominal revolution: 244/min, max. revolution 678/min,
Asynchronous generator nominal revolution 1010/min, max revolution 2798/min (15 min), belt drive, no gearbox!
Grid freq 50Hz
How is that possible that induction generator has that wide rev range?
Back to gearbox question, let'a say we have low speed Archimedes screw turbine 5-25 revolutions per minute (1-4m3/s flow) with 100kw max power and induction generator with nominal revolution 1000/min and 4 speed gearbox. Can someone give some info about gearbox ratios? Is it possible that let's say turbine at 10rpm produce 30kW but dispite gearbox generator at that slip would produce less power so turbine has to accelerate to appropriate slip but there is no enough water for higher turbine speed!
RE: Induction Genarator Frequency Control - Wind Turbine
The maximum rpm listed for a generator is the speed above which it should be expected to start self-destructing from centrifugal force.
Mike Halloran
Pembroke Pines, FL, USA
RE: Induction Genarator Frequency Control - Wind Turbine
I don't really follow your gearbox question. Whatever turbine speed the generator and gearbox set is the speed the turbine has to run at. You need controls to shut-down the unit so the generator doesn't become a motor when there isn't enough water to drive the turbine fast enough to produce power. It can take some work to properly match mechanical speed with generator speed to get the optimal output but it's nothing that isn't already well known and documented.
RE: Induction Genarator Frequency Control - Wind Turbine
Generator - Power goes into the motor shaft and it comes out of the electrical leads.
Motor - Power goes into the electrical leads and it comes out the motor shaft.
Now, every motor synchronous or induction wants to run at or very near its designed synchronous speed. See examples in the previous post. Connect to the shaft and try to force the machine to a speed below the synchronous speed and it will be a motor. Try to force the machine to a speed above the syncronous speed and it will be a generator. The only difference between induction and synchronous is that the synchronous machine is locked to the synchronous speed and the induction machine speed will vary by say 2% above or below synchronous speed as it switches from full power motoring to full power generating. It might swing from say 980rpm to 1020rpm for example.
RE: Induction Genarator Frequency Control - Wind Turbine
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Induction Genarator Frequency Control - Wind Turbine
RE: Induction Genarator Frequency Control - Wind Turbine
RE: Induction Genarator Frequency Control - Wind Turbine
When the internal voltage in the rotor leads the terminal voltage in the stator, the rotor magnetic field leads the stator magnetic field. In this case, the stator magnetic field is trying to pull back the rotor. That is, it is applying a torque to the rotor in the opposite sense from the velocity. This means that the product of the torque and velocity is negative, which indicates power flow out of the mechanical system, which is "generating". This power must go into the electrical system, where the voltage and current will have the opposite sign.