Hi,
I'm studying the possibility of a tidal river turbine. For this question, let's assume I have found the optimal TSR of the turbine, that I can adjust the output load any way I want, I need an AC output (need to send the electricity over 250 feet) and don't really care about the frequency of the output (assume I'll drive a resistance heater).
My river changes speed over a 6 hour time window. Let's say that I want to generate power with a turbine RPM ranging from 20 RPM to 60 RPM (a factor of three). Clearly I'll need some sort of gearing (any recommended high efficiency gearing??) around 30 to 1.
While I'm clearly no generator expert, I'll try to ask an intelligent question.
First, if I assume a fixed gear ratio, then the generator will be spinning from 600 RPM up to 1800 RPM. Does anyone have a rough plot of generator effiency vs RPM (I'm sure it depends upon the type of generator)?
Second, does anyone build a gearbox with an adjustable gearing ratio (basically a 2 or 3 speed transmission). I REALLY don't want to go there.
I've found plenty of graphs of overall efficiency of turbine systems, but none of just the generator. Since I can control the load, this means I can control the load on the turbine, but I need to learn more about the generator.
I want to run the turbine at it's peak effiency, but don't want to get killed by the generator.
Thanks,
Dave