How are armature reactions generated by direct current generators
How does the armature reaction affect the motor?
Magnetic field of the DC motor under load - armature reaction
After the DC motor is loaded, the armature winding has a current called the armature magnetic field, and the influence of the armature magnetic field on the main magnetic field is called the armature reaction, the specific analysis is as follows: when the motor is loaded, the current flows in the armature winding and The armature current creates the armature magnetic force. At this time, the air gap magnetic field of the motor is determined by the two magnetic fields of the main magnetic field and the armature. The occurrence of the armature magnetic force causes the air gap magnetic field to be distorted, i.e. H. The armature reaction. In a DC motor, the current of each branch is drawn through the brush regardless of the type of armature winding, so the brush is the limit of current distribution on the armature surface, the axis of the armature magnet potential always coincides with the brush axis.
1. Magnetic anchor potential in the axis axis Fa
The armature magnetic field is as shown on the left, when the current flows in the upper half of the armature, and the lower half flows according to the clockwise screw rule, the magnetic field generated by the armature magnetic force is indicated by the dashed line, it can be seen from the figure that the axis of the Armature magnetic force always coincides with the brush axis. The axis orthogonal to the major pole axis is usually called the intersection axis, and the axis coincident with the major pole axis is called the straight axis. When the brush is on the geometric neutral line, the armature magnetic force is armature magnetism.
2 the magnetic armature potential Fad of the straight axis
3, anchor reaction in a straight axis
When the motor is a generator, the brush moves in the direction of the beta angle, the direct axis armature reaction only exists when the brush is not in contact with the conductor at the geometric centerline, there is also an armature armature reaction at this point (armature analysis) (later analysis), and the influence of the magnetic armature potential of the direct axis armature is now analyzed separately.
If the motor is a generator, the brush will move in the direction of the beta angle.
★★ If the DC generator brush is shifted a small angle, the effect of the armature reaction on the main pole magnetic field will be demagnetized.
★★ If the brush of the DC generator is offset by a small angle, the effect of the armature reaction on the main pole magnetic field will be magnetized.
DC motor: The armature response of a DC motor is exactly the opposite of a DC generator; with DC motors, students can prove it for themselves.
4. Anchor reaction perpendicular to the axis
Regardless of whether the brush of the DC motor is in contact with the conductor at the geometric center line, the transverse axis magnetic potential Faq and its armature reaction are present.
Here, the normal axial position of the brush is taken as an example to illustrate the armature response. The idea is to use the Bo (x) wave of the magnetic density distribution wave and the Ba (x) wave of the armature magnetic density separation wave during the Synthesize load and obtain the synthetic air-gap magnetic density wave B (x), i.e.: bo (x) + ba (x) = b (x)
(1) In a DC generator, the armature reaction of the armature causes the front extreme to have a demagnetizing effect, and the latter has a magnetizing effect.
(2) In the DC motor, the front is extreme - extreme after magnetization - demagnetization
So what is the front extreme and the last extreme? For the generator, the extremes of the past are the extremes of the front, and the extremes of the latter are called the extremes. However, in this schematic diagram, if the direction of the magnetic field and the direction of the current of the Engine are unchanged, if the generator is switched to a motor, the steering must be changed, i. H. The front extreme for the DC generator and the extreme for the DC motor. The electromagnetic relationship within the motor is unchanged, so the AC armature reaction of the DC motor should conclude that the front extreme has a magnetizing effect and the latter extreme has one Has demagnetizing effect.
(3) In DC motors, the armature armature reaction has some saturation demagnetization, due to the influence of the magnetic saturation, the magnetization will increase the saturation of the core, and the magnetoresistance will increase, so the actual air gap magnetic field will be a little lower than that of the unsaturated state; while the Demagnetization is not saturated, the demagnetization is more magnetic, the magnitude of the value is large so it is closed (3).
5, DC motor armature reaction summary
(1) Anchor reaction across the axis
1 Distort the waveform of the main magnetic field.
2 has a certain degree of saturation of the demagnetization
(2) Anchor reaction in a straight axis (only available if the brush is offset from the theoretical position)
Influence of the armature reaction on the motor
The changing magnetic field generated by the energized stator winding causes the rotor to generate a current in closed loop control, and then the rotor generates a magnetic field that causes the magnetic field generated by the original stator winding to be superimposed, showing magnetization or demagnetization. Phenomenon, this phenomenon is reflected in the armature, due to the reason reflected by the armature, the magnetic field changes, which leads to a decrease in the quality of the air gap magnetic field, which adversely affects its mechanical properties.
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