Ever Power
DC motor
Two Parts
It is divided into two parts: stator and rotor. Note: do not confuse the commutator pole with the commutator.
Stator
The stator includes: main magnetic pole, frame, commutating pole, brush device, etc.
Rotor
The rotor includes: armature core, armature (Shu) winding, commutator, shaft and fan, etc.
What is DC motor
DC motor is a kind of motor that converts DC electric energy into mechanical energy. Because of its good speed regulation performance, it is widely used in electric drive. According to the excitation mode, DC motor can be divided into permanent magnet, separate excitation and self excitation, and self excitation can be divided into parallel excitation, series excitation and compound excitation.
Good speed regulation performance
DC separately excited motor
DC separately excited motor: there is no electrical connection between the excitation winding and the armature, and the excitation circuit is supplied by another DC power supply.
DC shunt motor
DC shunt motor: the circuit is parallel and shunt, and the voltage at both ends of the shunt winding is the voltage at both ends of the armature
DC series motor
DC series motor: the current is in series, the voltage is divided, and the excitation winding is in series with the armature, so the internal magnetic field of the motor changes significantly with the change of the armature current.
DC compound motor
DC compound motor: the magnetic flux of the motor is generated by the exciting current in two windings.
“Starting principle”
Because the resistance and inductance of the armature circuit of the motor are small, and the rotating body has a certain mechanical inertia, when the motor is connected to the power supply, the armature speed and the corresponding back EMF at the beginning of the starting stage are very small, and the starting current is very large. The maximum current can reach 15-20 times of the rated current. This current will disturb the power grid, mechanical impact the unit and spark the commutator. Therefore, direct closing starting is only suitable for motors with power less than 4kw (starting current is 6-8 times of rated current).
“Selection of characteristic type of DC motor”
(1) Constant torque production machinery (TL certain, independent of speed) to choose hard characteristics of the motor, such as: metal processing, lifting machinery.
(2) The mechanical load TL is proportional to the square of speed n. This kind of machinery should also choose the motor drive with hard characteristics.
(3) Constant power load (when p is fixed, t and N are inversely proportional), soft characteristic motor should be selected. Such as: electric locomotive, etc.
There are two ways to change the rotation direction of DC motor.
One is the armature reverse connection method, that is, the polarity of the terminal voltage of the excitation winding is kept unchanged, and the motor is reversed by changing the polarity of the terminal voltage of the armature winding;
The other is the reverse connection method of the excitation winding, that is, keeping the polarity of the voltage at the end of the armature winding unchanged, changing the polarity of the voltage at the end of the excitation winding to adjust the direction of the motor. When the voltage polarity of the two is changed at the same time, the rotation direction of the motor remains unchanged.
The armature reverse connection method is generally used to realize the positive and negative rotation of separately excited and shunt excited DC motors. The reason why the reverse connection of excitation winding is not suitable for separately excited and shunt excited DC motors is that the number of turns of excitation winding is large and the inductance is large. When the excitation winding is reversely connected, a large induced electromotive force will be generated in the excitation winding, which will damage the insulation between the switch and the excitation winding.
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