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 :)
bob g[ Parent ]
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 .......
Herb[ Parent ]
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 ]
