Lets actually push reactance inductance etc to background for moment. As the as the stator pole flux builts up due to the passing of the rotor magnet an emf would be induced into both windings as a load is connected to both a currents will try to flow. these currents will in turn pruduce another magnetic force mmf that will oppose the mmf of the rotor (Lenz's law) both coils will therefore combine together to oppose and reduce the rotor flux. Immportantly no flux will be produced by the currents in the coils as mmf is always going to be less than rotor mmf. Hence no back emf or transformer effect. ( no self inductance no mutual inductance ) The output emf will be reduced however as if there was inductance by the fact both coils oppose the rotor mmf. Even to the extend that phase shift will occur due to greatest opposition as current passing though zero. In conclusion IMHO the effect of winding coils in opposite directions and having separate but equal loads would bethe same as wound in same direction. Dueto there only being one flux from the rotor. The mmf from the coils cannot overcome this as they cease to exist if even equal. A very good query though and one that makes one go back to basics.
Will post now but bound to think of better way to explain as soon as i do
Herb[ Parent ]
If you want higher efficiency at a specific high speed then rewind with fewer turns of thicker wire. The less turns you have the lower the effects of armature reaction and leakage inductance.
Work the field hard and use the minimum turns to get what you want and that is the best you can do. Forget the bifilar windings but you may have to wind several wires in hand to get the wire cross section so you could connect each strand to its own rectifier just for fun, it will not be any different from paralleling the wires.
Run it at your speed ( 3800?) and try it into higher and higher voltage batteries until you find the peak power point, then divide the original turns by the ratio of optimum volts above 12. If 36v works best use 1/3 turns etc.
Good luck. Flux[ Parent ]
my target voltage is 120 line to line Y connected 3 phase at ~380 hz with the final product being AC and not DC
the slot fill with the original winding is about 75% or so, and i can go with much smaller wire. my hope is to replace the 7 turn/pole with 21 turns per pole which i think is doable.
with the increase in turn count i would expect higher slot leakage inductance but am thinking that current also plays a significant role perhaps i can triple the windings if i reduce the current by a factor of 4 or 5 with the net effect being reduced?
that i don't know for sure
this is why i was interested in bifilar i knew all along that i was faced with a rewind of the stator. and while most of the machine is technically locked in by design (i am not going to recut a stator core, or fabricate a rotor, etc.) winding however is something i can make a change in.
i am now thinking that perhaps it would be interesting to wind one phase bifilar as a test, then remove it and replace it with a standard double wound (2 in hand) convensional winding and compare the results.
in theory the bifilar method should reduce of eliminate the back emf in the stator (under load) and provide much less armature reaction (if you wanna call it that) whereas the standard winding under the same load would have a back emf established in the pole that bucks the flux across the gap. (here again i may be using the wrong terminology)
anyway, thank you very much for your input it is always appreciated
bob g[ Parent ]
thanks for the input
i would agree with your assertion in re to the coil once current is flowing creating an opposing magnetic field in the pole to that of the rotor pole, if you are using a single turn coil or two coils wound in the same direction. if however you use two coils that are wound opposite to one another their setting up a magnetic field in the pole would cancel each other out. with in theory no back field being generated.
what am i missing here,, it feels like i am just on the edge of understanding what you are stating, but can't quite grasp it yet.
you have given me something to think about :)
It certainly makes one think and get back to basics that many of us have either never studied or brushed aside. Most of the text books you refer to properly asssume basic knowledge. The discusion here is off track in the fact its confusing self inductance where the current flowing in a coil by itself can and will produce a flux. (note flux is like current mmf is like emf )this flux cuts coil creating a back emf - opposition Also Mutual inductance is mentioned this is where th above flux cuts another coil -transformer Neither of the above are in a generator as the flux flowing can only come from the rotor, if mmf from any coil equals rotor mmf no flux no induced emf. In your twin coil a mmf is set up by each coil but must both be in a common direction to oppose the one rotor mmf and resulting flux is reduced. Its not relevant that the coilsare wound in different directions currents will flow to create opposing mmf to rotor and as they can not produce a actual flux themselves self inductance is not a issue. bifolar is a means canceling self inductance . Here we have inductance yes but due to rotor flux. Its much easier to follow the theory in transformers where the flux is produced by the primary winding. Read up sometheory on transformers, I just looking though my old books most authors do avoid discussing fundementals of inductance in generators. another term i have seen here armature reaction was originally given to DC machines its the distortion of the rotor flux due to the opposing mmf it caused the brush position to be incorrect as load increased. only effect in our generators is crowds flux to a smaller pole face in fact with air cores no real effect. Leakage flux is when the opposing mmf makes it easier for the rotor flux to bypass the coil. All the effects tend to reduce output voltage as load comes on. Inductance of the rotor coil combination is the main cause though in our small units, we often kill the rotor flux creating the flatterning of of out put current.
Enough .......
If the coils are separate it doesn't matter in the slightest which way they are wound, you have 2 windings each supplying a load, if you reverse one coil you will reverse the phase of the external emf, but each load will still contribute in opposing the rotor mmf.
Think of a transformer with 2 secondaries, if you connect them opposing you get nothing out. If you connect them in parallel and in phase and ran 2 10W bulbs you would have exactly the same thing as each secondary running a 10 watt bulb. If you wound 0ne secondary the other way the thing would still see the same load with separate windings.
Flux[ Parent ]
If you are rectifying then the rectifier presents lagging pf. You may see marginal improvement by adding capacitors across the lines to bring pf leading. Unfortunately again saturation will prevent you seeing much improvement and the higher leading current will increase the resistive loss.
Now as you are using high voltage and high frequency I am going to offer you one ray of hope, if you use SERIES capacitors then if you can get the right value you should form a series resonant circuit with the leakage inductance and it should cancel leaving only R. I can't promise that this will work but it does in the case of a phase converter and you can raise the third leg voltage quite a bit. Normally the capacitor values are beyond reality but in your case it may not be so bad.
How much of the inductive voltage limiting has to do with efficiency is unclear to me.
Certainly for constant power output the effect is not a lot, but if you want to extract the maximum power out at the 50% efficiency point, it will certainly drop the output power away from the KVA = ~rpm^2 curve.[ Parent ]
