question

Hi @3toddr

I've been thinking about this for awhile.

I was torn between a setup you've described above ie where turbine outputs voltage/frequency for direct usage. ie 240vac single phase 50hz and you manage those conditions as you describe above.

Compared to the route I've seen lots of microhydro systems go.

Where they generally have several smaller penstocks and several smaller micro hyro generators (sized so that they can freespin without risk of damage so you don't need to worry quite as much about quite as robust dump load infrastructure).

These micro hydro generators are generally three phase and are bridge rectified to DC then passed into a MPPT controller which feeds a battery. Which is then inverted to 240vac to use. Rather than outputting the 240vac 50hz like your proposed system.

I'm honestly not sure what the better system is so curious to see what responses you get.

First 1 works without a battery and only needs one penstock pipe/generator.

Second you can use a 3phase generators, and multiple of them. You can probably control output easier without needing to adjust loads to keep frequency/voltage in check. Given you've got lots of smaller pipes rather than one big one you can probably get cheaper more consumer products/electronic valves. However it does rely on a battery and has a few extra conversion steps to get to 240vac.

Very jealous you're able to build the system. If you're anywhere near South Wales I'm happy to lend a hand. Itching to gain experience working on such systems, even if I'm only needed for donkey work!

The key thing is maintaining the line frequency and protecting the generator/turbine itself from overspeed (or underspeed). We have an oldschool flyball governor on the system that will keep the turbine spinning at less than about 610rpm or so (12 pole, 3 phase generator, produces a nominal 60Hz). The load shedding system, in turn, acts a bit like a loadbank governor and keeps the line frequency closer to 60Hz by controlling every hot water tank and boiler heating element in town. If the frequency starts getting too high, it can force excess power into the boilers in the large buildings. If the line frequency gets too far out of whack, the protective relays kick in and drop the generator, causing the mechanical governor to do its thing and deflect water, protecting the turbine from overspeed.

The problem with smaller scale direct generation is dealing with load transients. In direct generation you’re literally relying on the rotational momentum of the generating system to carry you through while the governor reacts. If you’re spinning 1000kg of metal, this is practical. If you’re just spinning something small, not so much. Depending on the time of year, our water can get low enough that someone turning on an oven or a clothes dryer causes enough of a frequency drop that the protective relays kick in and kill the power. We’re looking at adding a Eaton microgrid inverter/charger to resolve this.

The problem you’d have with using something like an MPPT is I don’t know how well it would react to a) the non-DC voltage of even rectified 3 phase, and more importantly, if your batteries get full, the input to an MPPT typically goes open circuit, which would unload your generator potentially causing it to overspeed.

If you’re going really small scale, say 20kVA or less, another option would be to treat the generator more like an automotive alternator (even using a large frame alternator) and use something like a Wakespeed WS500 to modulate the excitation current. You’d still need a mechanical governor to protect the turbine/generator, but that would probably be better than trying to go through something that wasn’t designed for it.