An armature is a component of a motor that is equipped with wires. Because of the relative motion of the wires through the magnetic field between the pole pieces, causing the current induced in the wires (as in the generator) or causing magnetic induction through the wires, it is here. Rotate in the magnetic field (as in the motor). Only the DC motor has an armature, the armature includes an armature core and an armature winding, and the armature winding is a circuit part of the DC motor, and is also a part that induces an electric potential and generates electromagnetic torque for electromechanical energy conversion (the generator is mechanical energy converted into Electrical energy). The armature core is both a part of the main magnetic circuit and sometimes a support member of the armature winding, and the armature winding is embedded in the slot of the armature core. The AC motor is a rotor. The principle of the induced armature of the DC motor and the AC motor is roughly the same. The current in the armature winding of the DC motor is also AC, and the output through the commutator is DC. The AC motor is divided into an induction motor (asynchronous machine) and a synchronous motor. The induction motor is divided into a squirrel cage rotor and a wound rotor according to the rotor structure. The induction motor generates a magnetic field by the stator winding, and the rotor winding performs electromechanical energy conversion. The synchronous motor generates a magnetic field in the rotor winding, and the stator winding performs electromechanical energy conversion.
When no current flows through the armature winding, the magnetic field formed by the magnetic pole is called the main magnetic field and is approximately sinusoidally distributed. When there is current in the armature winding, the winding itself generates a magnetic field called the armature magnetic field. The effect of the armature magnetic field on the main magnetic field will cause the main magnetic field to be distorted and generate an armature reaction;
(1) Armature reaction at purely resistive load
The electromotive force of the armature magnetic field is the same as the current phase, and the armature magnetic field distorts the main magnetic field, and the half is strengthened and half is weakened;
(2) Armature reaction at purely inductive load
The current of the armature magnetic field lags behind the electromotive force by 90 degrees. The electromotive force generated by the armature magnetic field is opposite to the electromotive force generated by the main magnetic field, thus weakening the main magnetic field electromotive force, which is why the voltage drops when the three-phase circuit contains an inductive component; Longitudinal demagnetization armature reaction
(3) Armature reaction at pure capacitive loading
The current of the armature magnetic field leads the electromotive force by 90 degrees. Since the armature magnetic field is 90 degrees to the main magnetic field, the electromotive force generated by the armature magnetic field is the same as the electromotive force generated by the main magnetic field, thus strengthening the main magnetic field electromotive force, which is why the three-phase circuit The reason why the terminal voltage rises when the capacitive element is contained; this is called the vertical axis auxiliary magnetic armature reaction.
The nature of the armature reactionThe armature reaction is divided into the direct-axis armature reflection and the symmetrical load of the cross-axis armature reaction. The influence of the armature magnetomotive force on the fundamental wave of the main pole magnetic field is called the armature reaction. Its main properties are demagnetization and no effect (this is for the main flux)
Magnetic field of DC motor under load - armature reactionAfter the DC motor is loaded, the armature winding has a current through it, referred to as 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 in the armature winding passes, and the armature current will generate the armature magnetomotive 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 appearance of the armature magnetomotive force causes the air gap magnetic field to be distorted, that is, the armature reaction. In a DC motor, regardless of the type of armature winding, the current of each branch is drawn through the brush, so the brush is the boundary of the current distribution on the armature surface. The axis of the armature magnetic potential always coincides with the brush axis.
1. Cross-axis armature magnetic potential FaqThe armature magnetic field is as shown on the left. If the current in the upper half of the armature is outflow and the lower half is inflow, according to the right-handed screw rule, the magnetic field established by the armature magnetomotive force is indicated by the dotted line. It can be seen from the figure that the axis of the armature magnetomotive force always coincides with the brush axis. The axis orthogonal to the main pole axis is usually called the intersection axis, and the axis coinciding with the main pole axis is called the straight axis; so when the brush is on the geometric neutral line, the armature magnetomotive force is the armature armature magnetism. Potential.
The figure above is a schematic diagram of the current distribution of the DC motor and the magnetic field of the armature. For the sake of analysis, it is expanded to the right.
Set the intersection point of the straight axis with the outer circle of the armature to 0, and make a closed magnetic line loop at x from 0 o'clock.
The closed circuit is studied according to the Ampere circuit law. The total current that can be enclosed by the closed circuit is the total magnetic potential Fa: because A is the number of ampere conductors per unit length along the circumference of the armature surface: Zaia
A=-------(Ampere conductor number/cm)
Za——the total number of conductors of the armature windings;
D——the outer diameter of the armature;
Ia - armature current
Then the total magnetic potential of the closed circuit is Fa=2xA, and the magnetic potential consumed by each air gap is Faq=A&TImes;x.
The distribution of the quadrilateral armature magnetic potential Faq(x) is a triangular wave (when the influence of the cogging is omitted), and the distribution waveform of the armature magnetic density is - "saddle" wave. As shown in the right figure ba(x).
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