2.2 kw single phase motor in south africa automotive vehicles
The performance of DC motor is closely related to its excitation mode. Generally, there are four excitation modes of DC motor: DC separately excited motor, DC parallel excited motor, DC series excited motor and DC compound excited motor. Master the characteristics of the four methods:
1. DC separately excited motor:
The excitation winding has no electrical connection with the armature, and the excitation circuit is supplied by another DC power supply. Therefore, the excitation current is not affected by the armature terminal voltage or armature current.
2. DC shunt motor:
The voltage at both ends of the shunt winding is the voltage at both ends of the armature, but the excitation winding is wound with thin wires with a large number of turns, so it has a large resistance, making the excitation current passing through it small.
3. DC series motor:
The excitation winding is connected in series with the armature, so the magnetic field in the motor changes significantly with the change of armature current. In order not to cause large loss and voltage drop in the excitation winding, the smaller the resistance of the excitation winding, the better. Therefore, DC series excitation motor is usually wound with thicker wires with less turns.
4. DC compound excitation motor:
The magnetic flux of the motor is generated by the excitation current in the two windings.
Left hand rule] left hand rule is also called "motor rule". It is a rule to determine the force direction of the energized conductor in the external magnetic field. The method is to stretch out the left hand so that the thumb is perpendicular to the other four fingers and on the same plane as the palm. Imagine putting your left hand into the magnetic field so that the magnetic line of force enters the palm vertically, and the other four fingers point to the direction of current. At this time, the direction pointed by your thumb is the direction of the force of the magnetic field on the current. The right-hand rule is also known as the "generator rule". A rule for determining the direction of the induced current in a conductor when it moves in a magnetic field. Stretch out the stone hand so that the thumb is perpendicular to the other four fingers and is in the same plane as the palm. Suppose you put your right hand into the magnetic field, let the magnetic line of force enter vertically from the palm of your hand, and make your thumb point to the direction of conductor movement. At this time, the direction indicated by the other four fingers is the direction of induced current.
Right hand rule
right-hand rule
For the cross product of a vector, we define
A × B=C
Note that the order of a and B cannot be reversed
Let the direction of vector a follow the back of the hand and vector b follow the direction of four fingers, then the direction of vector C is the direction of thumbs up (perpendicular to the plane formed by a and b)
This is the right-hand rule.
Keep your right hand flat so that your thumb is perpendicular to the other four fingers and is in a plane with your palm. Put your right hand into the magnetic field. If the magnetic force line vertically enters the palm (when the magnetic induction line is a straight line, it is equivalent to the palm facing the N pole), the thumb points to the moving direction of the conductor, and the direction indicated by the four fingers is the direction of the induced current in the conductor.
In electromagnetics, the right-hand rule mainly judges the direction independent of force.
If it is related to force, it all depends on the left-hand rule.
That is, the left-hand rule for force and the right-hand rule for others.
Current element i1d ι Pair distance γ Another current element i2D of 12 ι The acting force DF12 is:
μ 0 I1I2d ι two × (d ι one × γ 12)
df12 = ── ───────────
4π γ one hundred and twenty-three
Where d ι 1、d ι 2 is the direction of current; γ 12 is from i1d ι Point to i2D ι Radial vector of. Ampere's law can be divided into two parts. One is the current element ID ι (i.e. i1d above) ι ） stay γ (i.e. above) γ 12) The magnetic field generated at
μ 0 Id ι × γ
dB = ── ─────
4π γ three
This is bi SA LA's law. Thee scond is the current element IDL (i.e. i2D above) ι 2) The force DF received in the magnetic field B (i.e. DF12 above) is:
df = Id ι × B
2.2 kw single phase motor in south africa automotive vehicles
（1） Good speed regulation performance. The so-called "speed regulation performance" refers to that the speed of the motor is artificially changed according to the needs under the condition of a certain load. DC motor can realize uniform and smooth stepless speed regulation under heavy load, and the speed regulation range is wide.
（2） Large starting torque. The speed regulation can be realized uniformly and economically. Therefore, all machinery that starts under heavy load or requires uniform adjustment of speed, such as large reversible rolling mill, winch, electric locomotive, tram, etc., are driven by DC motor.
The principle of "the force acting on the energized conductor in the magnetic field" is roughly applied. The two end wires of the excitation coil have the same current in the opposite direction, which makes the whole coil produce the torsion around the shaft and make the coil rotate.
To make the armature receive an electromagnetic torque with the same direction, the key is: when the coil side is under the magnetic poles of different polarity, how to change the direction of the current flowing through the coil in time, that is, the so-called "commutation". Therefore, a device called commutator must be added. The commutator and brush can ensure that the current in the coil side under each pole is always in one direction, so that the motor can rotate continuously. This is the working principle of DC motor
It is divided into two parts: stator and rotor. Remember that the stator and rotor are composed of those parts. Note: don't confuse the commutator with the commutator, and remember the functions of them.
Stator includes: main magnetic pole, base, commutation pole, brush device, etc.
The rotor includes: armature core, armature winding, commutator, shaft and fan, etc.
2.2 kw single phase motor in south africa automotive vehicles
The excitation mode of DC motor refers to the problem of how to supply power to the excitation winding and generate excitation magnetic flux to establish the main magnetic field. According to different excitation modes, DC motors can be divided into the following types.
1. Separately excited DC motor
The excitation winding is not connected with the armature winding, but the DC motor supplied by other DC power sources to the excitation winding is called separately excited DC motor, and the wiring is shown in figure (a). In the figure, M represents the motor, and if it is a generator, G represents it. Permanent magnet DC motor can also be regarded as separately excited DC motor.
2. Shunt DC motor
The excitation winding and armature winding of Shunt DC motor are connected in parallel, and the wiring is shown in figure (b). As a shunt excitation generator, the terminal voltage from the motor itself supplies power to the excitation winding; As a shunt motor, the excitation winding and armature share the same power supply, which is the same as that of separately excited DC motor in terms of performance.
3. Series excited DC motor
The excitation winding of the series excited DC motor is connected in series with the armature winding, and then connected to the DC power supply. The wiring is shown in figure (c). The excitation current of this DC motor is the armature current.
4. Compound DC motor
Compound excitation DC motor has two excitation windings of parallel excitation and series excitation, and the wiring is shown in figure (d). If the magnetic flux generated by series excitation winding is in the same direction as that generated by parallel excitation winding, it is called cumulative compound excitation. If two magnetic fluxes have opposite directions, it is called differential compound excitation.
DC motors with different excitation modes have different characteristics. Generally, the main excitation modes of DC motor are parallel excitation, series excitation and compound excitation. The main excitation modes of DC generator are separate excitation, parallel excitation and compound excitation.
2.2 kw single phase motor in south africa automotive vehicles
Three alternating currents are connected into the motor stator to generate a rotating magnetic field at a speed of N0. Different pole pairs P, under the action of AC with the same frequency f = 50Hz, will produce different synchronous speeds N0, N0 = 60F / P.
The speed of the motor rotor is less than that of the rotating magnetic field, which is basically the same as that of the induction motor. s=(ns-n)/ns。 S is the slip rate,
NS is the magnetic field speed and N is the rotor speed.
According to different rotor structures, three-phase asynchronous motors can be divided into cage type and wound type.
Cage rotor asynchronous motor has been widely used because of its simple structure, reliable operation, light weight and low price. Its main disadvantage is the difficulty of speed regulation.
The rotor and stator of wound three-phase asynchronous motor are also equipped with three-phase windings, which are connected with external rheostat through slip ring and brush. Adjusting the rheostat resistance can improve the starting performance and adjust the speed of the motor
Advantages: compared with single-phase asynchronous motor, three-phase asynchronous motor has the advantages of simple structure, convenient manufacture, good operation performance, saving various materials and low price.
Disadvantages: lagging power factor, low light load power factor and poor speed regulation performance.
The three-phase asynchronous motor has high power and is mainly made into large motor. It is generally used in large industrial equipment with three-phase power. First of all, three-phase asynchronous motors are only used for motors, rarely used as generators, and synchronous motors are used for power generation.
For low-power three-phase asynchronous motors below 1kW, they can operate not only in three phases, but also in single phase.
The rule for determining the direction of induced current in the conductor moving in the external magnetic field is also known as the generator rule. It is also the judgment rule of the relationship between the direction of induced current, the direction of conductor movement and the direction of magnetic line of force.
Handshake is applicable to the rule that the palm of the generator is in the direction of the magnetic field, the thumb is in the direction of the object movement, and the finger is in the direction of the current ~ ~ ` determine the direction of the dynamic electromotive force generated in the conductor when the conductor cuts the magnetic induction line. The right hand rule is: stretch out your right hand,
Make the thumb perpendicular to the other four fingers and in a plane with the palm of your hand. Put your right hand into the magnetic field and let the magnetic induction line penetrate vertically
The palm and thumb point to the direction of conductor movement, and the other four fingers point to the direction of dynamic electromotive force. Direction and generation of electromotive force
The direction of induced current is the same.
The direction of electromotive force determined by the right-hand rule conforms to the law of energy conversion and conservation.
Precautions for applying the right hand rule
When applying the right-hand rule, it should be noted that the object is a straight wire (of course, it can also be used for the energized solenoid), and the speed V and magnetic field B should be perpendicular to the wire, and V and B should also be perpendicular,
The right-hand rule can be used to judge the direction of induced electromotive force. For example, the right-hand generator rule can be used to judge the direction of induced electromotive force of three-phase asynchronous motor rotor.
The reason for the right-hand rule is that electricity, magnetism and quality constitute three dimensions. The right-hand rule represents the electric dimension, magnetic dimension and quality information gradient dimension.
2.2 kw single phase motor in south africa automotive vehicles
Because the induced current in the rotor coil of three-phase asynchronous motor is generated due to the relative movement between the rotor conductor and the magnetic field. The rotor speed of three-phase asynchronous motor will not be synchronized with the rotating magnetic field, let alone exceed the speed of the rotating magnetic field. If the speed of the rotor of the three-phase asynchronous motor is equal to the speed of the rotating magnetic field, there will be no relative movement between the magnetic field and the rotor, and the conductor cannot cut the magnetic line of force. Therefore, there will be no induced electromotive force and current in the rotor coil, and the rotor guide of the three-phase asynchronous motor will not be affected by the electromagnetic force in the magnetic field to make the rotor rotate. Therefore, the rotor rotation speed of three-phase asynchronous motor cannot be the same as that of rotating magnetic field, and is always less than the synchronous speed of rotating magnetic field. However, under special operation mode (such as power generation braking), the rotor speed of three-phase asynchronous motor can be greater than the synchronous speed.
Symmetrical 3-phase winding is connected with symmetrical 3-phase current to generate rotating magnetic field. The magnetic field wire cuts the rotor winding. According to the principle of electromagnetic induction, e and I are generated in the rotor winding. The rotor winding is affected by electromagnetic force in the magnetic field, that is, electromagnetic torque is generated to rotate the rotor, and the rotor outputs mechanical energy to drive the mechanical load to rotate.
In AC motor, when the stator winding passes through AC current, the armature magnetomotive force is established, which has a great impact on the energy conversion and operation performance of the motor. Therefore, the three-phase AC winding is connected with the three-phase AC to generate the pulsating magnetomotive force, which can be decomposed into the sum of two rotating magnetomotive forces with equal amplitude and opposite speed, so as to establish the sum of forward and reverse magnetic fields in the air gap. These two rotating magnetic fields cut the rotor conductor and generate induced electromotive force and induced current in the rotor conductor respectively.
The current interacts with the magnetic field to produce positive and negative electromagnetic torque. Forward electromagnetic torque attempts to make the rotor rotate forward; The reverse electromagnetic torque attempts to reverse the rotor. The superposition of these two torques is the synthetic torque that drives the motor to rotate.
