1) Synchronous motors can be divided into: permanent magnet synchronous motors, reluctance synchronous motors and hysteresis synchronous motors.
2) Asynchronous motors can be divided: induction motors and AC commutator motors.
Induction motors can be divided into three-phase asynchronous motors, single-phase asynchronous motors and shaded-pole asynchronous motors.
The AC commutator motor can be divided into:
Single-phase series-excited motor, AC/DC dual-purpose motor and repeller motor.
According to the starting and running modes, it can be divided:
Capacitor-starting single-phase asynchronous motor, capacitor-operated single-phase asynchronous motor, capacitor-starting single-phase asynchronous motor, and split-phase single-phase asynchronous motor.
It can be divided according to the purpose: drive motor and control motor.
1) Drive motor can be divided: electric tools (including drilling, polishing, polishing, grooving, cutting, reaming, etc.) with electric motors, household appliances (including washing machines, electric fans, refrigerators, air conditioners, recorders, video recorders) , motors, vacuum cleaners, cameras, hair dryers, electric razors, etc.) Motors and other general small mechanical equipment (including various small machine tools, small machinery, medical equipment, electronic equipment, etc.) motor.
2) The control motor is divided into: a stepping motor and a servo motor.
What should be paid attention to when selecting the motor: 1. Principle of selecting the motorIn order to adapt to various purposes, motor manufacturers produce motors of different types, forms and capacities. When selecting motors, consider their characteristics. After carefully studying the characteristics of the machine being driven, select the motor that suits the load characteristics.
The principle of choosing a motor is:
(1) According to the starting characteristics and operating characteristics of the load, the motor that is most suitable for these characteristics is selected to meet various requirements in the working process of the production machine.
(2) Selecting a motor that has a protection mode and a cooling mode that is compatible with the environment of the place of use, should be structurally suitable for the environmental conditions in which the motor is located.
(3) Calculate and determine the appropriate motor capacity. Motors that are typically designed and manufactured are most efficient at 75%-100% rated load. Therefore, the difference between the capacity required by the equipment and the capacity of the selected motor should be minimized, so that the power of the motor is fully utilized.
(4) Select a motor with high reliability and easy maintenance.
(5) Considering interchangeability, try to choose a standard motor.
(6) In order to make the whole system operate at high efficiency, it is necessary to comprehensively consider the number of poles and voltage level of the motor.
(1) Select the type of motor according to the requirements of production mechanicality.
(2) Select the rated voltage of the motor according to the power supply.
(3) Select the number of revolutions of the motor according to the number of revolutions required by the production machine and the condition of the transmission equipment.
(4) Select the structure and protection form of the motor according to the location and location environment of the motor and production machinery.
(5) Select the rated power of the motor according to the power capacity required for the load and the operating mode of the motor.
When making the motor selection, we must prepare a number of manufacturers and brand catalogues at hand, and then consider the above factors to select the most suitable motor.
The motor is reversing, it seems to be just a simple circuit diagram, but it contains a lot of common knowledge of electricians. Therefore, this picture is often used as an introductory teaching for electricians, or it is an enlightenment material for many electricians. Today, I will share it with an electrician friend who is interested in the electrician or just entered the line.
This picture is also used directly, such as cranes, hoists, lathes, elevators, etc. Machines that need to do round-trip movements almost always need to use positive and negative. Technology has developed to the present day, many machines have realized automation, such as CNC lathes, etc., all use plc control, but need to know, PLC in the programming process, the programmer must be clear about its mechanical control principle, in order to pass the control circuit during programming To achieve control functions. We have the opportunity to share the PLC control program that controls the motor's forward and reverse rotation, but it is absolutely necessary to learn the mechanical principle before learning the PLC.
In the schematic diagram of the motor forward and reverse control, the related knowledge points are: 1. The reason for the change of the direction of rotation of the motor; 2. The circuit protection device; 3. The component principle of the button and the contactor; 4. The self-locking and interlocking; The use of mechanical interlocks.
Motor forward and reverse circuit diagram (hereinafter referred to as Figure 1) â–¼
In this picture, the left side is the main circuit, which actually provides a power supply to the motor; the right side is the control loop, or the "secondary loop" (the control loop belongs to the secondary loop), which is through the use of buttons and contactors. Features control of the circuit.
In order to facilitate the gradual understanding of all aspects of knowledge, we split the circuit diagram, so there is the following picture (hereinafter referred to as Figure 2)
â–¼Motor rotation direction change reason
The leftmost circuit diagram is the same as the main circuit of the complete circuit above, and the three diagrams a, b, and c on the right side will be explained later. Here we look at the main circuit first. It can be seen from KM1 and KM2 that the reason why the motor can change the direction of rotation is because the order of the three-phase electric motor is changed here. That is, when KM1 is closed, the three phases of the motor from left to right are L1, L2, L3; when KM2 is closed, the three phases of the motor from left to right are L3, L2, L1. Hereinafter, it is specified that the order of L1, L2, and L3 is positive.
Circuit protection deviceStrictly speaking, including self-locking and interlocking, there is protection for the circuit. Only the protective components are mentioned here.
As can be seen more intuitively in Figure 1, the circuit has a 2P fuse FU2 and a 3P fuse FU1 and a thermal relay FR, both of which provide overload protection for the circuit.
The principle of buttons and contactorsButtons and contactors are the most used components in electrical control and are the main players in this picture.
The buttons are divided into a start button and a stop button. The start button is normally disconnected, closed when pressed, resumed after release, and the stop button is reversed. If you look closely at the control loop of Figure 1, you can see that SB1 is the stop button, but SB2 and SB3 look a bit strange, seemingly a start button, but below it draws two normally-closed contacts that lead to the side loop. In fact, the SB2 and SB3 here are two special buttons - mechanical interlock buttons. It is characterized by two contacts that are normally open and normally closed. When the button is pressed, the normally open contact closes and the normally closed contact opens.
There are coils, normally open contacts and normally closed contacts in the contactor, and the code numbers in the circuit diagram are all KM. The characteristic is that when the coil is powered off, the normally open contact is opened, and the normally closed contact is closed; after the power is turned on, the normally open contact is closed, and the normally closed contact is opened.
Self-locking and interlockingLet us look at the control loop of Figure 2a. At this time, press SB2 and the coil KM1 is energized. At this time, the contactor normally open contact KM1 is closed, so when the SB2 is released, the motor can still rotate forward-self-locking.
However, there is a problem at this time, that is, when the motor is in the forward rotation process, pressing SB3 will cause a short circuit accident (the contactor normally open contacts KM1 and KM2 in the main circuit are simultaneously closed, resulting in a short circuit). Therefore Figure 2a is an error connection.
In order to avoid such a short circuit, we cite the connection of Figure 2b. In this control loop, when the motor is rotating forward, since the contactor coil KM1 is energized, the normally closed contact KM1 is turned off, so even if SB3 is pressed at this time, the circuit does not have any reaction - interlock.
Mechanical interlocking
In fact, the control method of Fig. 2b can already realize the forward and reverse rotation of the motor, but the trouble is that when the motor forward rotation is reversed, the stop button SB1 must be pressed to continue pressing SB3. Therefore, for the convenience of operation, we have introduced a mechanical interlock button to make the circuit of Figure 2c.
In this figure, by pressing SB3, SB2 can be directly disconnected to reverse the motor.
Motor forward and reverse physical map â–¼
When using the circuit of Figure 1 or Figure 2c, pay attention to the place of use. In the case that some motors cannot be directly reversed during forward rotation, this circuit is not suitable to avoid danger.
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