motor as generator

[debdeb]

Hello,

I am designing an inexpensive water current turbine. This hydro installation only use the water speed of water to generate electricity.
As I already have 3 phase motors (1.5kW, 2850 RPM, 220/380-420V), I was wondering if I can convert them into generators for the turbine. These generators are expected to produce electricity for various speed. Is it possible? How can I do that?

 

[eemotor]

You may want to take a look at

http://www.qsl.net/ns8o/Induction_Generator.html

to see how to use an induction motor as a generator.

 

[corrosivo]

To answer your question simply, YES, there in nothing that will prevent an induction motor become an induction generator, but there are some conditions: 1. the rotor must be run at full load at higher speed than the motor nameplate speed >3000 rpm (50 hz.) 2. you must have access to the electrical grid because induction generators must be excited by an external ac source. There are other considerations, your turbine mechanical hp or kw must be smaller than the generator kw rating, you do not want to drive a generator with a bigger prime mover, your motor speed is not the best for this use unless you use speed increaser for your turbine, the site characteristics will tell you the capacity of your system, such as the head and flow of the site. You do not need a governor with this system as the power output will depend of how fast you run the generator (within limits)the frequency will be of the electrical grid.
If you do not have access to the grid then this type of motors can't be used, you need synchronous motors (gen.) and some kind of speed governor and exciter, there are other considerations such as electrical and mechanical protection for the equipment etc.
There is a site you can check

http://microhydropower.net

 

[aolalde]

You need those motors connected to the three phase system with the proper voltage and frequency, driven by a water turbine. Increase the speed of the turbine to approximately 3150 rpm to produce 1.5 KW (full load) if the speed increases further you will be overloading the machine up to around 3 kW were the magnetic break down of the motor is reached and the motor will disengage from the synchronous magnetic field. Under that condition the current is very high with almost null power production. Now, if the speed is under 3000 rpm, the motor is driving the turbine taking energy from the electric utility.
This type of machine produces only real power, the reactive power required to generate the magnetic field is provided by the utility. The frequency is controlled by the utility power too.