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Armature Whole
Brush shift in dc machines
BRUSH SHIFT IN A DC MACHINE
It is known that armature reaction shifts the MNA by an angle(say ‘a') in the direction of rotation for a generator and opposite to the direction of rotation for a motor. This angle depends upon the magnitude of armature (load) current. Thus, the coils undergoing commutation will have an emf induced in them. As a result -poor commutation and sparking.
But if the brushes are given a shift so that GNA and MNA coincide again, then the emf induced in the coils undergoing commutation will be zero. This is the reason to shift the brushes.
Armature flux is along the GNA. When the brushes are shifted, GNA is shifted and thus the armature flux is also shifted. So now it has two components- vertical component causing demagnetization, and horizontal component causing cross magnetization. Thus the overall value of the flux per pole is reduced from its no load value, even without saturation.
Now out of the total conductors present in the armature, these are divided into two groups- one causing demagnetization and the other causing cross magnetization. It has been proved mathematically that conductors contained in 4*a degrees for every 360 degrees cause demagnetization, while the remaining cause cross magnetization. So if there is no brush shift, mathematically there is no demagnetization effect.
Also, if one sees the flux density waveforms, than it is seen that the flux per pole is reduced if the brushes are given a forward shift in case of a generator and backward shift in case of a motor. The term ‘forward shift' is used in the sense that the brushes are shifted along the direction of rotation in case of generator. In motors, these are shifted opposite to the direction of rotation, and hence ‘backward shift' is used.
However, if the brush shift is too high, than the field flux is reduced by a significant amount and thus affects the working of the generator or the motor. Due to the reduction in the flux, generator emf is reduced and in case of motor, the rotor speed is increased. Hence brush shift is no longer used now. It has been replaced by interpoles.
About the Author
electrical engineering student
Do engine armatures have bridge rectifiers in them?
Ok I'm just going to explain the whole situation. I have this armature from a weed whacker and I decided to power it with a large coil from an electric motor. It gives off a good arc, about a half inch. But I don't want to make it bigger. I want to increase the arc length with a capacitor. Someone suggested using a Leyden jar. I figured that would work just fine, but it doesn't and I'm not sure why. I thought that maybe it's because the current I'm using might be AC. But I'm pretty sure armatures have rectifiers in them. Do they, and if they do, do you have any idea why my setup isn't working?
Engines don't use electricity to function.
"Devices converting heat energy into motion are referred to as engines, which come in many types. A common type is a heat engine such as an internal combustion engine which typically burns a fuel with air and uses the hot gases for generating power. External combustion engines such as steam engines use heat to generate motion via a separate working fluid."
http://en.wikipedia.org/wiki/Engine
Teddy Undress