I was being shown a new hydro plant at our local river a few days ago (From the outside) The Project Manager was saying that the speed was finely regulated by the water flow to give the right frequency. (That was as technical as he could go on the topic).
This meant that in time of high flow it is throttled back considerably. Isn't it possible to generate DC and convert it electronically to AC? Wouldn't this mean that higher speed would give more amps?
yebbut it costs more and river flow generation is lousy on output anyway.
In days of yore alternators linked to the mains had to be synchronised and every alterntor runs/ran at exactly the same speed. Power output is increased not by increasing the speed but by increasing the torque. As long as the excitation is correct ,it is impossible for the alternator to run at any other speed once locked in (ie on line) If the excitation current is too low, the magnetic "bond" can break and"pole skipping" occurs which can damage the machine.
However these days the output from small altenators is rectified to DC and then connected to the mains with a special "grid tie inverter". All these solar PV arrays and most wind turbines have grid tie inverters.
Huge grid tie inverters are now available.
Maybe he meant that at *full* flow the generator would exceed the designed output and overheat?
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A major advantage is that the alternator can run at variable speeds and non synchronous speeds. Also it overcomes the problem of instabitly in the grid as the inverter is controlled by the grid rather than vice versa.
The turbine will be sized/set up so it can't overload the alternator whatever happens.
This is balls. But it *was* a Project Manager.
I'm sure you are correct, but the electronics to do this could be hard to design and may well be not that efficient. It kind of depends on the size of the power generation I'd imagine. I also wondered if some form of drive abit like Daf used in their automatic cars might work.
Brian
Maybe one could have different ways of driving the generator depending on the flow rate in some way.
Brian
DerbyBorn expressed precisely :
In the old days, to put a generator (alternator) on line, they would have to match the speed of the generator to the mains frequency and the phases. One method used lamps connected between the two sources, to match them so the lamps went out and stayed out. No difference in volts between the two, meant that the lamps were out with no flickering, speed and phases were therefore matched - at which point the generator to would be connected. Once connected they would stay in sync, output could then be increased so the unit was exporting power to the grid.
Nowadays, things are very different. It is all done automatically and smaller generators use inverters feeding units which convert back to AC with everything matched up.
Large rotating machinery has a speed limit anyway. There's a capacity limit to the amount of water/load and the hydro generator should be matched closely to the water allowed to flow through it - in any case, the upper sluices and the turbine inlets are sized to only allow this, with some fine variation as the bloke said. If you want extra power, you add more units or build bigger ones in the first place.
The electronics is all bog standard off the shelf nowadays. No moving parts, no maintenance.
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