Just -after- posting I noticed the above image applies only to two-speed motors, not the common induction induction motor.
Peter.[ Parent ]
Large commercial machines often used two motors with different pole numbers. The snag is that pole change motors are something of a compromise and are costly. The changeover switches puts a star/delta change into the shade and people here don't even seem capable of contemplating even that.
Flux[ Parent ]
You mean w.r.t. performance or complication of building/switchover?
Could the mill be by default in the best position for low wind output. Then above a given amperage, relays could be activated to switch configuration for as long as you get enough output?
MartinEau, soleil, le vent[ Parent ]
But from Flux's reply I understand that the switch-over for dual-speed motors is complicated. I tried googling the web for suitable wiring and switching diagrams but couldn't find any.
Below is a drawing I made a few weeks ago for star/delta switchover using contactors. It needs 3, but K1 is not part of the actual star/delta switching; it's a fail-safe which always shorts output unless positively energized. As you can see, just for simple star/delta switching it takes 3 contactors (well, ok, just two for the actual star/delta).
The generator will also need a tacho-sensor (not shown in this partial schematic) and some electronics to actually energize the contactors. Not rocket science but more complicated than just hardwiring for either star or delta.
Also, it would mean running 6 wires down the tower. Or one would have to install the contactors and rectifiers at the top, but then it would still need a few wires to control the contactors. When using sliprings it would take 6...
Peter.
(K1 & K2 are normally closed (NC) contactors, K3 is normally open (NO) [ Parent ]
Why can't you epoxy or conformal coat the entire box and achieve reliable operation. It seems the money saved in 4 lengths of wires should make up for the extra effort.[ Parent ]
Just that it would still need several control lines (to control the contactors) running down the tower, along with the DC + and - lines.
For ease of maintenance and repair I'd like to have the contactors and rectifiers on ground level though.
The rotor is in this case happy to go along with the pole change... in fact a three phase and single phase 4pole, 2pole rotor is the same animal and depending on what forces are operating on it, decides the pole no (bit hazy about this ).
Your conversion rotor is static in its pole spacing and coverage area, so I'm not sure how this would work if at all.
Should work for an induction motor acting as a genny, (with exciter caps) but???? for a conversion.
.........oztulesFlinders Island Australia[ Parent ]
Oz is correct, this can only work on a cage rotor, it just doesn't work with permanent magnet rotors. Anyway it was a bit tongue in cheek as the complexity is beyond anything reasonable.
I understand you would have to run 6 wires instead of 3 if the rectifiers are down the tower or instead of 2 if they are up but couldn't these wires be smaller since each of them takes less current?
Also, instead of having a tacho sensor with wires up and down the tower, couldn't it be simply some device to measure the output from the mill (I guess in current would be best) and trigger the contactors above a given current value?
Thanks for helping me understand,
Martin eau, soleil, le ventEau, soleil, le vent[ Parent ]
Assuming that in all three cases the same amount of power would be lost in the wiring:
In the case of 3 lines (AC) coming down the tower vs. 2 (DC) coming the tower: yes, with 3 wires (more or less in parallel) you could use thinner wires and still end up with the same line loss. The new wires could be 20% or 25% less in diameter. I'm not sure which of the two figures is correct, still pondering that myself and won't get into detail here, as I'm already accused of thread hijacking. The difference is mainly academic anyway.
In the case of 6 lines (with star/delta at ground level) vs. 3 lines coming down the tower, since the wires are now in series (2 sets of 3 wires), each of the 6 wires would actually have to be thicker than the wires in the 3-line-AC system. Since total length of the wires is now doubled, area of each wire should be double too (or in other words, diameter should be (sqrt(2)) = 1.41 as large.
At least, if I understand things correctly. If not I'll be no doubt corrected by others :)
http://www.windstuffnow.com/main/3_phase_basics.htm
