Re: Might be wet in the west...

Edward <eddien@xxxxxxxxxxxxxx> writes
In message <xY2DOuAf47jHFwIx@xxxxxxxxxxxxxxxxxxxx>
Oz <Oz@xxxxxxxxxxxxxxxxxxxx> wrote:

Edward <eddien@xxxxxxxxxxxxxx> writes

Most of the switchgear is in the house but it still ages just the same.

Bizarre. I've never come across that before.
What ages, and how?
Well, the voltage regulator board had to be replaced and was upgraded
to frequency regulation. No, I don't know why, just that the gain
slope is steeper.

I still don't see why it ages.

OK. I imagine a brushless alternator is just a standardish 3ph motor run
backwards?

Clearly not, see later.

Presumably this is sealed, fan cooled (may not be necessary)
with just one bearing where moisture could ingress.
I don't think so.

Er, no. Its a more sophisticated thing I have no knowledge of...

It has field windings which are fed with rectified
current

Ok, so this must set up a dc magnetic field for the rotor to rotate in
and thus induce the rotor current and thus the rotating magnetic field.

via diodes which are supplied with ac by the exciter windings.
These are supplied with about 18v at 1a by a black box which looks
after these things.

Ok, I can't find an electrical design for a generator without brushes,
but several descriptions of designs with a dc excitor coil. I imagine
that the magnetic field is largely controlled by this winding. We did
have (two) generators here but they had brushes, I think to power the
rotor, and a bunch of diodes. If you didn't run it for a few years there
wasn't enough residual magnetism left in the core to start it up, and
you had to flash a car battery through a coil (always a tad scary at 1am
in a storm).

That had to have a transistor replaced. It has a
giant heat sink on one end of the box.

I like it!

I. E. The field regulator, mounted on the wall of the hut, takes its
current from the output, and rectifies it to approx 18v, adjusting
both current and voltage, by reading the ac voltage. This goes to the
exciter part and energises the stator coils which give ac in the field
section of the rotor.

OK

This is rectified by diodes mounted on the
shaft and fed to the rotating field windings on the main part of the
rotor.

Er, if its brushless, how do you get power to a rotating winding???

Seems to me that this 18V rotor section is simply the rotating
electromagnet. In which case its a simple device again. Increase the
current in the rotor and you increase the magnetic field which increases
the output from the stator and increases the load on the wheel.

These produce ac in the main stator which gives the final 240v
ac output.

Hokey dokey.

You will note that there are 2 controllers in the system, field
regulator and ballast regulator. They can end up working against each
other causing wild oscillations.

Sure. Being magnetic the load from the stator WILL induce current in the
rotor (hopefully minimised as far as reasonable) which can either cause
power to increase or decrease. Its not hard to see how positive feedback
could happen.

You stop that by having the right
amount of ballast dump available to match the output of the genny,
approx 120 percent of the output in kw.

OK.

This means that you have to
alter the ballast load when you alter the genny output by adjusting
the valve openings. This applies, even if you are taking most of the
output into the priority circuits.

Can't you just leave total ballast on max?
If not can't you have more power zones so you can have two ballasts?

As a safety device, the field regulator has an over/undervoltage trip
in the circuit, which switches off the excitation if the output gets
outside the parameters.

Sensible.

There is a relay in that black box which
sometimes refuses to latch on when starting after an outage. The cure
for that is to clean the contacts with a piece of thin card.

No, the cure is to use a higher spec device. In this case probably gold
plated everything, surprisingly cheap. Even a fully sealed relay (spare
kept in the house). All relays worth bothering with will plug in.

The whole thing is mounted on a
rectangle of 8 inch channel with the turbine hanging below in a bottomless
box, the vee drive in the channel and the alternator mounted on top.

ascii art: must be viewed with a monospaced font like courier.


=======motor======
|| | ||
|| | ||
|| | ||
|| |<v belt ||
|| | ||
|| | ||
|| | ||
======pelton=======



--
| | pipe
--

Um!! The 2 shafts are vertical. The belt is horizontal. Think drum
mower, I think!

OK, so its really easy then. The generator can be kept in a more-or-less
sealed room with just the shaft going through the wall. A small
dehumidifier (eg an old fridge) keeps the RH low in that area. Heck, you
can probably get away with coldwater pipework within the room.

The
penstock is 1000 feet of 8 inch plastic with the 9m sections glued together
giving 200 feet of head.

Thassa lota warta! Lessee, what does my mears slipstick say?

330m with 200mm pipe.
200' = 6bar

about 220 l/s = 1/4 ton/sec

abt 7.4m/sec.

Assuming I have slipsticked it all right that's a total energy of

1/2 mv^2 = 6845 joule/sec = watts.

That seems way too low, 7kW.

lets try mgh = 250x10x330 = 825kW

AHA! Most of the energy above is lost in the pipe.
Lets try losing only 3 bar to an orifice.

Now we are only doing 160 l/s.

But we have 3 bars we can convert to kinetic energy that will give us
1/4 of the total energy we had before or about 200kW. Of course one
could refine this further but I'll bet that's not far off the optimum.
Given pressure losses in pipes go as a power law, probably a bit less
flow still.
It uses 1 cufoot per second and gives about 12kw.

It should be capable of vastly more unless you are short of water.
1 cuft/sec is about 30 l/sec whilst the full-bore flow of your 200mm
pipe should be about 250 L/s.

Anyhow given that at this flowrate losses will be negligible (my
calculator suggests about 0.2 bar) then you have the full 6 bar across
the nozzle. So, 6 bar = 600,000 Pa = 600,000 N/m^2
energy is pressure x vol = 600,000 x .03 (m^3) = 18000 joules

available power is thus 18kW, so overall efficiency is 67% nominal.

Which I would say was pretty good.

The 3 nozzles were
about 3/4 inch at manufacture but after 28 years, have enlarged so
only 2 nozzles are used to drive the genny at rated output. This will
cause some inefficiency as they are no longer matched to the wheel
correctly.

It shouldn't be hard to make up some new nozzles.

You could have about another 4 wheels if you wanted...

However, it's free, so, provided there is enough water
most of the time, I don't worry. Replacing the nozzles is not as big
a job as replacing the turbine bearings, which last about 10 years.

Damaged by rust or just wear out?

The genny bearings last about the same time but it goes to the
rewinder for replacement.

Yup. And presumably a rebake and a reseal.

From what I saw its a miracle its even watertight!
And WHAT a quarry!
I think you are probably thinking of the Prince of Wales quarry.

The one at the top of the valley?

Mine
is very small fry.

Oh. I didn't see any others I can remember.

There was a mill race up the RHS of the valley (IIRC).
Maybe that was another valley and another quarry.

The Centre for Alternative Technology has one of the same type but a
smaller size. Maybe there is a picture on their website?

No. Crappy site seems keener on earning money than telling anyone
anything.

--
Oz
This post is worth absolutely nothing and is probably fallacious.



.

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