# Pelton Turbine selection

1. Jul 24, 2011

### I_am_learning

When I have a certain head (H) of water, this fixes the jet velocity of water as
V = sqrt(2gH). And for maximum energy transfer, turbine bucket velocity should equal,
V(b) = V/2.
Now, I am confused at how do you determine the Turbine diameter and no. of Poles to be used in the generator.
I mean, you could go for, smaller diameter (hence higher RPM to maintain V(b) = V/2) and so, choose lower poles generator (to maintain 50 Hz output), OR you could go for large diameter (hence lower RPM to maintain V(b) = V/2) and choose higher Poles generator (to maintain 50Hz output).
How do you decide?
Thanks

2. Jul 24, 2011

### 256bits

I would think that desired power output would be a factor in the size of Pelton wheel.

3. Jul 25, 2011

### I_am_learning

Yes power must come into consideration, but I can't find how.
Can somebody also explain me about specific speed, it seems to be necessary here. Wiki says, the specific speed of a turbine is the speed at which a geometrically similar unit would run if it were exposed to Q = 1 and H = 1.
How does that help me?

Last edited: Jul 25, 2011
4. Jul 26, 2011

### 256bits

I am not a Pelton wheel expert but

Power : Pmax = ρghQ

So from that, and solving for Q, the volume flow rate, you know how much fluid the buckets of the Pelton wheel need to discharge, and necessarily their size. ( There must be a guideline to find that out somewhere which gives optimal size )
This is in relation to the nozzle size which has to discharge Q at the bucket, and you can calculate the nozzle diameter, or more specificialy the jet diameter, and a corresponding bucket size. Note that you can add more jets for increased power, or for the same power decrease the jet size with multiple jets.

As for the number of poles on the generator, someone versed in electrical generators might answer that in more detail, but i would imagine it has something to do with volts, current, and how much copper wire you can wind around the poles in the generator in the given space, taking into account the current carrying capacity of the wire.

Specific speed relates to dimensional analyis comparing one turbine to another geometrically similar - scale model to the real thing quite possibly, or adding another turbine to an existing facility. I am not sure if that helps you out as you seem to be designing from scratch.

I hope that helps you get started.
Please take into account that I am out on a linb here.