Ac Motor used as a generator on wind turbine
Ac Motor used as a generator on wind turbine
(OP)
Hi
I don't have any real experience in this area but i have been looking at a job where a 37Kw 4pl IEC Ac Motor, rated voltage range 380-420D/660-725Y 50Hz is being proposed to run as a generator using soft starts for starting. The motors will be driven by the wind turbine generating 28Kw. My question is this, is a std Ac motor with std windings ok for this job. The proposed motor is a Siemens 37Kw 4pl B3 cast iron asynchronous induction motor with std windings. Any thoughts would be welcome.
I don't have any real experience in this area but i have been looking at a job where a 37Kw 4pl IEC Ac Motor, rated voltage range 380-420D/660-725Y 50Hz is being proposed to run as a generator using soft starts for starting. The motors will be driven by the wind turbine generating 28Kw. My question is this, is a std Ac motor with std windings ok for this job. The proposed motor is a Siemens 37Kw 4pl B3 cast iron asynchronous induction motor with std windings. Any thoughts would be welcome.





RE: Ac Motor used as a generator on wind turbine
As for motors, I have set up demonstrations a couple of times.
Once the results were excelent. Another time and place with different equipment, the results were still positive, but nowhere near as good as the first time.
I hope someone can tell us what properties of an induction motor are beneficial to use as an induction generator.
yours
RE: Ac Motor used as a generator on wind turbine
Waross, the reason for the soft starter is that typically the turbine cannot produce enough torque to start itself from a standstill. In order to avoid over speeding, the turbine blades are designed to shear off excess torque producing wind, and of course, it's that "excess" torque that is needed as accelerating torque. So they use the soft starter to get it up to motor slip speed, then bypass it with a contactor and let the turbine take it the rest of the way to super-synchronous. You are correct in that you can't have reverse current flow through a normal soft starter. There are however specially designed units specifically for the wind generator industry (Google Enerpro). Most users don't want to pay the extra money for them however, because a bypass contactor works fine and is cheap, and that way they can use an industry standard soft starter that they can quickly get a replaced or serviced.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Ac Motor used as a generator on wind turbine
But as an induction generator, it must be connected to the grid to generate power - it cannot operate in an isolated configuration, at least not very easily.
Also, as a generator, its power factor will be lousy (low). If this is a system that is going to actually run for long periods of time to produce power, you may want to consider adding some switched capacitors to help provide some of the excitation.
I'm guessing the motor will be the least of your problems. I agree with waross re the soft start - I'm not seeing the purpose for that, but I haven't thought about too hard - maybe I'm missing something. I don't think you'll be able to backfeed power through the softstarter, unless it has a bypass contactor.
RE: Ac Motor used as a generator on wind turbine
http://www.nrel.gov/docs/fy05osti/33138.pdf
As I said though, if you are connected to a grid, you don't need to worry about this.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Ac Motor used as a generator on wind turbine
Personally I would prefer a dc machine with a synchronous inverter to feed the grid. Turbine voltage and Rpm can fluctuate, but the inverter will respond very quickly.
RE: Ac Motor used as a generator on wind turbine
RE: Ac Motor used as a generator on wind turbine
RE: Ac Motor used as a generator on wind turbine
From a cost standpoint, AC regenerative inverters are typically only used in the biggest generators because they require a lot more capital, protection and maintenance, so you only see them in 400kW and up (last I checked). They do that because they want to maximize the revenue by taking advantage of low wind days where the turbine has trouble getting super-synchronous. On small induction generators it isn't worth the cost and headaches for the small amount of additional power you would get.
That's why small island mode wind turbines tend to be DC. They don't ned the additional complexity to make an AC induction generator work, even though brushes are a pain. You still need an inverter if your loads are AC, but it's a much simpler off-the-shelf inverter, really more like a chopper drive because it is just doing the DC to AC part of the job.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Ac Motor used as a generator on wind turbine
The blades will want to spin faster to produce more power if the wind increases. So, when you limit them to a fixed speed they tend to somewhat "stall" as the wind increases. But, they will still produce more power with a stronger wind so you will have to have some control means for them.
Using permanent magnet generators running wild seems to be the standard these days. Every turbine 10kW and under that I've looked at uses PM generation. Above that, it's a mix of technology but even the largest machines are using PM generation.
RE: Ac Motor used as a generator on wind turbine
My personal opinion is that it will not work. First it needs the greed voltage for excitation, the power factor is low consuming high reactive power from the greed and a super sophisticated fast mechanical control is required to connect it only when the speed is above synchronous, considering the typical wind performance.
The induction generators used in the windmill farms are not simple induction motors. Those are wound rotor induction machines which have a controller connected to the rotor winding to make the generating window broader. A detail of the operation is complicated to me for explanation here. May be you will find some information at:
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RE: Ac Motor used as a generator on wind turbine
RE: Ac Motor used as a generator on wind turbine
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Ac Motor used as a generator on wind turbine
aolalde is right, the wound rotor control seems to be the other main type of generator used. I forgot about that one.
RE: Ac Motor used as a generator on wind turbine
Here is a very informative article on the whys and wherefores of using induction generators on grid connected systems. Danish wind power technology link
Despite what the ABB drives division would like you to believe about the prevalence of inverters in induction generators, here is what ABB sells the most of world wide.
ABB induction generators link
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Ac Motor used as a generator on wind turbine