# Using self excited induction generator

#### windy

Joined Apr 19, 2007
26
I have been researching the use of self excited induction machines and have a few questions. what is needed to start the field in the rotor, or is there enough residual field to charge the capacitors.

what speed would be needed to make such a machine produce, I understand that variable speed is a plus of this type of machine.

I am building a small wind turbine

#### beenthere

Joined Apr 20, 2004
15,819
If you're going to buy the generator, then the manufacturer will have a data sheet that will answer these questions. I would imagine the residual magnetism in the armature will let it start up.

#### windy

Joined Apr 19, 2007
26
The Ebooks on AC that are presented on this site are what brought me here. However the Conference Paper NREL/CP-500-26713 is really what caught my eye.

In your Ebook, the procedure for starting the process confused me a little as it talks about fail safe opporation and not needing a master switch. (ref: AC Tesla induction motors). On the NREL Paper The residual Magnetism is implied but not stated in that no startup procedure is given.

I am not buying I am building, by the graphs given In the NREL there consern is grid tied, so they don't give data for lower voltages and this is my desire as I am not grid tied. My thoughts are to charge the battery bank of my system at lower wind speeds, and heating the house and water at higher output rather than shutting it down in heavy winds.

#### rajmasi

Joined Dec 23, 2008
1
hai all,
how model self excited induction generator in MATLAB/SIMULINK and where to start with, is there any forum for that suggest me

bye
raj

#### andy6

Joined Dec 3, 2009
1
There are a few types of self excited machine. With the mention of a capacitor bank I guess your using a conventional Induction Generator.
The minimum speed to get a useful power output is related to the torque speed characteristic of the machine.
Depending on the project - if it is connected to the grid directly it will have to run at a fixed speed, which is defined by the grid frequency and also the number of poles in the generating machine you use.
Anyway the minimum speed at which it will generate is known as the synchronous speed. Synchronous speed of the machine is the ratio of the voltage frequency to the number of poles scaled up by 120. There is a lot of info on this kind of thing on the net.

If you want it to generate power over variable speeds you will have to run the output through either full or partial power electronics (designed to change the frequency of voltage produced to the frequency of the grid your setup is feeding into)

I am currently doing a similar project but I am using a permanent magnet induction generator(these also are self excited the permanent magnet replaces the field winding) I am using this type of generator because it is small(only one winding) and the obvious example it is self excited (ie no reactive power is required from the grid to create a magnetic field) the field is already there due to the magnet

for further background read about other generator setups. Doubly-fed, Cage rotor etc.

Hope this helped. Im new here...

#### beenthere

Joined Apr 20, 2004
15,819
Welcome to AAC. You may find that we preserve old threads, so it's best to check dates before posting a reply.

#### GetDeviceInfo

Joined Jun 7, 2009
2,198
Residual is typically enough to provide some current to the field, which subsequently provides 'build up'. Your residual will weaken over time if the machine is not used, and at some point you may have to 'flash' the field with DC current to re establish some residual.