The set up

The set up
5.46mm jet delivering 0.68 l/s to the pelton which is rotating at 900 rpm and generating 135 watts into the grid.

Monday, 13 April 2015

Reduced core stator: Part 2

The performance of the new stator has been almost wholly pleasing.  I made no alterations to the pelton nozzles between changing stators so comparison of one with the other was possible. The flow into the turbine was therefore a constant, namely 1.51 lps. Here are the things I observed:

1. Power: rather than being better, was 8% worse. This was the only disappointment.  I attribute it to the efficiency of the alternator being poorer when 24 of its poles have been cut off:

2. The quality of the power was markedly smoother, presumably because at the lower MPPV, the inverter was better able to fix on a maximum power point and hold to it: (note the scale in the lower trace, which is from the 18 pole stator, is different from the trace above, hiding the extent to which the trace is better.)

3. MPPV settled at about 145 v; before it was around 370 v; current rose proportionately from about 1.1 to about 2.4 amps:

4. Shaft rpm, shown here at 1079, later settled at about 1100 ± 4 once the grease had warmed up and been spread about, higher than the 968 ± 4 seen with the former stator:

5. In keeping with this higher measured shaft speed, the splash pattern from the pelton showed the changes expected. The bottom jet has moved to the left of the centre line whereas before, it was to the right; the top jet doesn't seem to have changed at all:

6. During a 24 hour period, there is still a slow undulation in the trace of power output, being just 7w peak to trough. What the cause of this is, I don't yet understand:

My big hope now after installing this new stator is that as summer approaches and water diminishes, I will be able to continue generation for more weeks than was previously possible.  Before, once flow got down to below 1.2 lps, I had to stop generating.  The excitement will be in discovering how low a flow I can go to.  Bring on the dry weather !

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