Thank you, this particular post has been quite helpful..
The fact that you told me that the penstock should be full to the top -- it's
stuff like that that I didn't know.. (remember, I'm relatively new to this).
Also, it seems like many people talk about "induction generator" -- now, is
that an AC generator?
--daniel
Donald/Elizabeth Scarlett <[EMAIL PROTECTED]> wrote:
Daniel's site has a head of 120ft. I worked with about 100 ft of head
when I built a 140W DC system several years ago. It utilized an alternator
and a bronze Harris pelton wheel directly mounted on the shaft. This was
unsatisfactory because the commutator would last only about 15 months before
wearing so badly that the alternator had to be replaced--usually in
mid-winter under very inconvenient conditions.
After receiving a lot of advice and help from Jeff Ankenman, who works
under the name, "Homestead Hydro Systems," I ended up replacing the
alternator with a Baldor (recommended for efficiency and because it rarely
needs re-flashing) three phase 1800 rpm induction motor wired for 208 volts.
I think it was 2 hp, sized to run cool. It wasn't too hard to modify the
Harris turbine case and re-mount the pelton on the motor shaft.
Run-type capacitors were used (the 1C-2C method) to balance phases and
improve efficiency while transmitting single phase AC power on the original
two transmission wires. The distance from the powerhouse to the house was
about 350 ft. At the house I installed a 500 VA transformer, 240 to 16 VAC,
then a bridge rectifier on a heat sink to produce up to 16 VDC, which then
went to the Trace C40 battery voltage regulator which had been used by the
old alternator system.
The nice thing about this arrangement is that as long as the penstock
head is sufficient to achieve an rpm somewhere near the rated rpm of the
generator, the voltage produced by the generator will self-adjust to about
240 VAC. In this case I recollect it was in the 215 VAC range. This is
because the power has to go somewhere--i.e. to the battery, and the battery
charging voltage (14+ volts) defines the transformer output voltage, which
in turn fixes the transformer input voltage (which is the transmission
voltage). The frequency was within 5 Hz of 60 Hz and will tend to be held
there by the loading managed by the Trace C40.
In this case I was pleased to eliminate the transmission wire voltage
drop (which with the DC system had been close to 15%) and, due to the
greater efficiency of the induction motor as generator, produce nearly 250W
instead of the 140W I had been getting from the DC alternator. In Daniel's
case the voltage drop at 240 VAC should be manageable with a reasonable
sized wire even at 800 ft.
Daniel asked about performance at lower flow. It is essential to set
the nozzle size at the turbine to the lowest expected flow rate. The
penstock must stay full to the top at all times if you want trouble free
operation. This is generally not hard to do.
This gives an outline of one solution to inexpensive generation for
battery charging when the transmission line is long. Even if the powerhouse
were adjacent to the house, I would use an induction generator rather than a
DC alternator just because it has no brushes and commutator to wear out.
Regards,
Don Scarlett
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