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What is a motor

What is a motor?

Motor is an electromagnetic device that converts or transmits electric energy according to the law of electromagnetic induction.
The motor is represented by the letter M (D in the old standard) in the circuit. Its main function is to generate driving torque. As the power source of electrical appliances or various machinery, the generator is represented by the letter G in the circuit. Its main function is to convert mechanical energy into electrical energy.

Classification of motors

1. According to the type of working power supply: it can be divided into DC motor and AC motor.

  • 1) According to the structure and working principle, DC motor can be divided into brushless DC motor and brushless DC motor.
  • Brushless DC motor can be divided into permanent magnet DC motor and electromagnetic DC motor.
  • Electromagnetic DC motor is divided into series excited DC motor, parallel excited DC motor, separately excited DC motor and compound excited DC motor. Permanent magnet DC motor is divided into rare earth permanent magnet DC motor, ferrite permanent magnet DC motor and aluminum nickel cobalt permanent magnet DC motor.
  • 2) AC motor can also be divided into single-phase motor and three-phase motor.

2. According to the structure and working principle, it can be divided into DC motor, asynchronous motor and synchronous motor.

  • 1) Synchronous motor can be divided into permanent magnet synchronous motor, reluctance synchronous motor and hysteresis synchronous motor.
  • 2) Asynchronous motor can be divided into induction motor and AC commutator motor.
  • Induction motor can be divided into three-phase asynchronous motor, single-phase asynchronous motor and shaded pole asynchronous motor.

AC commutator motor can be divided into single-phase series excitation motor, AC/DC dual-purpose motor and repulsion motor.
3. According to the starting and operation modes, it can be divided into: capacitor starting single-phase asynchronous motor, capacitor running single-phase asynchronous motor, capacitor starting running single-phase asynchronous motor and split phase single-phase asynchronous motor.
4. It can be divided into drive motor and control motor according to purpose.

  • 1) Motors for driving can be divided into: Motors for electric tools (including drilling, polishing, polishing, slotting, cutting, reaming and other tools), household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers Motors for electric shavers and other general small mechanical equipment (including various small machine tools, small machinery, medical instruments, electronic instruments, etc.).
  • 2) Control motor is divided into stepping motor and servo motor.

5. According to the structure of rotor, it can be divided into cage induction motor (called squirrel cage induction motor in the old standard) and wound rotor induction motor (called wound induction motor in the old standard).
6. According to the operating speed, it can be divided into high-speed motor, low-speed motor, constant speed motor and speed regulating motor. Low speed motors are divided into gear reduction motors, electromagnetic reduction motors, torque motors and claw pole synchronous motors.
In addition to the stepwise constant speed motor, stepless constant speed motor, stepwise variable speed motor and stepless variable speed motor, the speed regulating motor can also be divided into electromagnetic speed regulating motor, DC speed regulating motor, PWM Variable frequency speed regulating motor and switched reluctance speed regulating motor.
The rotor speed of asynchronous motor is always slightly lower than the synchronous speed of rotating magnetic field.
The rotor speed of synchronous motor is always kept at synchronous speed regardless of the load.

DC type

The working principle of DC generator is to change the alternating electromotive force induced in the armature coil into DC electromotive force when it is led out from the brush end by the commutator with the commutation of the brush.
The direction of the induced electromotive force is determined according to the right-hand rule (the magnetic induction line points to the palm of the hand, the thumb points to the movement direction of the conductor, and the direction of the other four fingers is the direction of the induced electromotive force in the conductor).

Working principle of DC generator

The force direction of the conductor is determined by the left-hand rule. This pair of electromagnetic forces forms a torque acting on the armature. This torque is called electromagnetic torque in rotating motor. The direction of torque is counterclockwise in an attempt to make the armature rotate counterclockwise. If this electromagnetic torque can overcome the resistance torque on the armature (such as resistance torque caused by friction and other load torque), the armature can rotate counterclockwise.
DC motor is a motor that depends on DC working voltage. It is widely used in tape recorders, video recorders, DVD players, electric shavers, hair dryers, electronic watches, toys and so on.

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Real drawing of DC motor

Electromagnetic type

Electromagnetic DC motor is composed of stator pole, rotor (armature), commutator (commonly known as commutator), brush, casing, bearing, etc,
The stator magnetic pole (main magnetic pole) of electromagnetic DC motor is composed of iron core and excitation winding. According to the different ways of excitation (called excitation in the old standard), it can be divided into series excited DC motor, parallel excited DC motor, separately excited DC motor and compound excited DC motor. Due to different excitation modes, the law of stator pole flux (generated after the excitation coil of stator pole is energized) is also different.
The excitation winding and rotor winding of series excited DC motor are connected in series through brush and commutator. The excitation current is directly proportional to the armature current. The magnetic flux of stator increases with the increase of excitation current, the torque is approximately proportional to the square of armature current, and the speed decreases rapidly with the increase of torque or current. The starting torque can reach more than 5 times of the rated torque, the short-term overload torque can reach more than 4 times of the rated torque, the speed change rate is large, and the no-load speed is very high (it is generally not allowed to run under no-load). The speed regulation can be realized by connecting the external resistor in series (or in parallel) with the series excitation winding or connecting the series excitation winding in parallel.
The excitation winding of Shunt DC motor is connected in parallel with the rotor winding, the excitation current is relatively constant, the starting torque is directly proportional to the armature current, and the starting current is about 2.5 times of the rated current. The speed decreases slightly with the increase of current and torque, and the short-time overload torque is 1.5 times of the rated torque. The speed change rate is small, which is 5% ~ 15%. The speed can be adjusted by weakening the constant power of the magnetic field.
The excitation winding of separately excited DC motor is powered by an independent excitation power supply, its excitation current is also relatively constant, and the starting torque is directly proportional to the armature current. The speed change is also 5% ~ 15%. The speed can be increased by weakening the constant power of the magnetic field or reduced by reducing the voltage of the rotor winding.
In addition to the shunt winding, the stator pole of the compound excitation DC motor is also equipped with a series excitation winding connected in series with the rotor winding (with a small number of turns). The direction of magnetic flux generated by the series winding is the same as that of the main winding. The starting torque is about 4 times of the rated torque, and the short-time overload torque is about 3.5 times of the rated torque. The speed change rate is 25% ~ 30% (related to series winding). The speed can be adjusted by weakening the magnetic field strength.
The commutator blade of the commutator is made of alloy materials such as silver copper and cadmium copper and molded with high-strength plastic. The brush is in sliding contact with the commutator to provide armature current to the rotor winding. The brush of electromagnetic DC motor generally adopts metal graphite brush or electrochemical graphite brush. The iron core of the rotor is made of silicon steel sheets, generally 12 slots, embedded with 12 groups of armature windings. After each winding is connected in series, it is connected with 12 commutators respectively.

DC motor

A rotating device that converts direct current energy into mechanical energy. The motor stator provides magnetic field, the DC power supply provides current to the rotor winding, and the commutator keeps the direction of rotor current and torque generated by magnetic field unchanged. According to whether there is a common brush commutator, DC motors can be divided into two categories, including brush DC motors and brushless DC motors.
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Brushless DC motor is a new type of DC motor developed in recent years with the development of microprocessor technology, the application of new power electronic devices with high switching frequency and low power consumption, the optimization of control methods and the emergence of permanent magnet materials with low cost and high magnetic energy level.
Brushless DC motor not only maintains the good speed regulation performance of traditional DC motor, but also has the advantages of no sliding contact and commutation spark, high reliability, long service life and low noise. Therefore, it has been widely used in aerospace, CNC machine tools, robots, electric vehicles, computer peripherals and household appliances.
According to different power supply modes, brushless DC motor can be divided into two categories: square wave brushless DC motor, whose back EMF waveform and power supply current waveform are rectangular waves, also known as rectangular wave permanent magnet synchronous motor; The back EMF waveform and supply current waveform of sine wave brushless DC motor are sine wave.

Working principle of DC motor

An annular permanent magnet is fixed inside the DC motor, and the current generates ampere force through the coil on the rotor. When the coil on the rotor is parallel to the magnetic field, the direction of the magnetic field will change. Therefore, at this time, the brush at the end of the rotor contacts the conversion plate alternately, so the direction of the current on the coil also changes, and the direction of the generated Lorentz force remains unchanged, So the motor can keep rotating in one direction.
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The working principle of DC generator is to change the alternating electromotive force induced in the armature coil into DC electromotive force when it is led out from the brush end by the commutator with the commutation of the brush.
The direction of the induced electromotive force is determined according to the right-hand rule (the magnetic induction line points to the palm of the hand, the thumb points to the movement direction of the conductor, and the direction of the other four fingers is the direction of the induced electromotive force in the conductor).
The force direction of the conductor is determined by the left-hand rule. This pair of electromagnetic forces forms a torque acting on the armature. This torque is called electromagnetic torque in rotating motor. The direction of torque is counterclockwise in an attempt to make the armature rotate counterclockwise. If this electromagnetic torque can overcome the resistance torque on the armature (such as resistance torque caused by friction and other load torque), the armature can rotate counterclockwise.

Control principle of DC motor

The control principle of BRUShless DC motor, to make the motor rotate, the first control part must be based on the location of the motor rotor detected by the Hal-sensor, and then according to the stator winding decided to open (or close) the sequence of power transistors in the inverter (Inverter), Inverter AH, BH, CH(these are called the upper arm power transistor) and AL, BL, CL(these are called the lower arm power transistor), the current flows through the motor coil in order to produce forward (or reverse) rotating magnetic field, and the rotor magnet interaction, so it can make the motor in time/reverse rotation. When the motor rotor rotates to the position where another set of signals are detected by the Hall-sensor, the control part turns on the next set of power transistors, so that the circulating motor can continue to rotate in the same direction until the control part decides to stop the motor rotor and turn off the power transistor (or only turn on the power transistor of the lower arm). If the rotor of the motor is reversed, the power transistor is turned on in reverse order.
The opening method of the basic power transistor can be illustrated as follows: AH, BL group →AH, CL group →BH, CL group →BH, AL group →CH, AL group →CH, BL group, but never open into AH, AL or BH, BL or CH, CL. In addition, because the electronic parts always have a switch response time, so the power transistor on and on the staggered time to take the response time of the parts into account, otherwise when the upper arm (or lower arm) is not completely closed, the lower arm (or upper arm) has been opened, the result is caused by short circuit and the power transistor burned down.
When the motor is running, the control department compares (or calculates by software) the speed of the hal-sensor signal to the Command (which consists of the set speed of the driver and the add/decrease rate) and the speed of the change of the hal-sensor signal. Then the next set (AH, BL or AH, CL or BH, CL or…) is determined. Switch conduction, and conduction time. Speed is not enough to open long, speed is too short, this part of the work is completed by PWM. PWM is to determine the speed of the motor fast or slow way, how to produce such A PWM is to achieve more accurate speed control of the core.
The speed control of high speed must take into account whether the CLOCK resolution of the system is enough to grasp the time of processing software instructions. In addition, the data access mode of hall-sensor signal changes also affects the efficiency of the processor, the correctness of judgment and the real-time performance. As for speed control at low speed, especially at low starting speed, because the hall-sensor signal changes back, it is very important how to retrieve the signal, how to process the signal, and how to properly configure the control parameter values according to the motor characteristics. Or the speed return change takes the encoder change as a reference to increase the signal resolution in order to get better control. The motor can run smoothly and respond well, and the appropriate P.I.D. control can not be ignored. As mentioned earlier, the BRUShless DC motor is controlled by a closed loop, so the call back signal is equivalent to telling the control unit how far the motor speed is from the target speed, which is the Error. Knowing the error will naturally be compensated, the way is traditional engineering control such as P.I.D. control. However, the state and environment of the control are actually complex and variable, and the factors to be considered for the robustness of the control may not be fully mastered by traditional engineering control, so fuzzy control, expert system and neural network will also be incorporated into the intelligent P.I.D. An important theory of control.

Permanent magnet type

Permanent magnet DC motor is also composed of stator magnetic pole, rotor, brush, shell, etc. the stator magnetic pole adopts permanent magnet (permanent magnetic steel), ferrite, aluminum nickel cobalt, neodymium iron boron and other materials. According to its structural form, it can be divided into cylinder type and tile type. Most of the electric used in the recorder and player are cylindrical magnets, while most of the motors used in electric tools and automotive appliances use special block magnets.
The rotor is generally made of silicon steel sheets, which has fewer slots than the rotor of electromagnetic DC motor. Most of the low-power motors used in the recorder and player are 3 slots, and the higher grade ones are 5 slots or 7 slots. The enamelled wire is wound between two slots of the rotor core (three slots means three windings), and its joints are respectively welded on the metal sheet of the commutator. Brush is a conductive part connecting the power supply and rotor winding. It has two properties: conductivity and wear resistance. The brush of permanent magnet motor uses single metal sheet or metal graphite brush and electrochemical graphite brush.
The permanent magnet DC motor used in the recorder and player adopts electronic speed stabilizing circuit or centrifugal speed stabilizing device.

Brushless DC

Brushless DC motor uses semiconductor switching devices to realize electronic commutation, that is, electronic switching devices are used to replace the traditional contact commutator and brush. It has the advantages of high reliability, no commutation spark and low mechanical noise. It is widely used in high-grade recording stand, video recorder, electronic instruments and automatic office equipment.
Brushless DC motor is composed of permanent magnet rotor, multipole winding stator, position sensor, etc. Position sensing converts the current of stator winding in a certain order according to the change of rotor position (that is, detect the position of rotor magnetic pole relative to stator winding, generate position sensing signal at the determined position, control the power switch circuit after being processed by the signal conversion circuit, and switch the winding current according to a certain logical relationship). The working voltage of the stator winding is provided by the electronic switch circuit controlled by the output of the position sensor.
There are three types of position sensors: magnetic sensitive, photoelectric and electromagnetic. For brushless DC motor with magnetic position sensor, its magnetic sensor components (such as hall element, magnetic diode, magnetic sensitive transistor, magnetic resistor or special integrated circuit, etc.) are installed on the stator assembly to detect the change of magnetic field caused by the rotation of permanent magnet and rotor.
For the brushless DC motor with photoelectric position sensor, the photoelectric sensor is configured on the stator assembly according to a certain position, the rotor is equipped with a shading plate, and the light source is light-emitting diode or small bulb. When the rotor rotates, due to the action of the shading plate, the photosensitive components on the stator will generate pulse signals intermittently at a certain frequency.
Brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonant circuit, etc.) on the stator assembly. When the rotor position of permanent magnet changes, the electromagnetic effect will make the electromagnetic sensor produce high-frequency modulation signal (its amplitude changes with the rotor position).

Superiority

Dc motor has a rapid response, large starting torque, rotating speed of from zero to rated speed can provide the rated torque performance, but the advantages of dc motor is also its drawback, because the direct current machine to produce a constant torque under the rated load performance, the armature magnetic field and rotor magnetic field must be constant to maintain 90 °, this is about to borrow from the carbon brush and commutator. The brush and commutator will generate sparks and toner when the motor is rotated, so in addition to causing component damage, the application is also limited. Ac motors do not have carbon brush and commutator, maintenance free, rugged, widely used, but in order to achieve the characteristics of the equivalent of DC motor performance must use complex control technology to achieve. With the rapid development of semiconductors, the switching frequency of power components is much faster to improve the performance of the driving motor. Microprocessor speed is also getting faster, can realize the ac motor control in a rotating two axis direct intersection coordinate system, appropriate control of the ac motor in two axis current component, similar to dc motor control and have the same performance with dc motor.
In addition, there are many microprocessors will control the motor necessary functions in the chip, and the volume is getting smaller and smaller; Analog to digital Converter (ADC), Pulse wide modulator (PWM)… And so on. The BRUShless DC motor is an application that electronically controls the commutation of the AC motor and obtains characteristics similar to the DC motor without the absence of the DC motor mechanism.

Control structure

Brushless DC motor is a kind of synchronous motor, that is to say, the rotor speed of the motor is affected by the speed of the stator rotating magnetic field and the number of rotor poles (P) :
N =120. F/p. When the number of poles of the rotor is fixed, the rotor speed can be changed by changing the frequency of the stator rotating magnetic field. Brushless DC motor is the synchronous motor plus electronic control (driver), control the frequency of the stator rotating magnetic field and the speed of the motor rotor feedback to the control center for repeated correction, in order to achieve close to the characteristics of the DC motor. That is to say, brushless DC motor can be in the rated load range when the load changes can still control the motor rotor to maintain a certain speed.
Dc brushless drive includes power supply and control, power supply to provide three-phase power to the motor, the control part according to demand conversion of input power frequency.
The power supply can be directly input with dc (generally 24V) or ac (110V / 220V). If the input is AC, it must be converted to DC by the Converter. Whether direct current input or ac input to the motor coil before the first dc voltage converter (Inverter) into 3 phase voltage to drive the motor. Inverter (Inverter) is generally divided into 6 power transistors (Q1 ~ Q6) upper arm (Q1, Q3, Q5)/ lower arm (Q2, Q4, Q6) connected to the motor as a switch to control the flow through the motor coil. The control part provides PWM (pulse width modulation) to determine the switching frequency of the power transistor and converter (Inverter) commutation time. Brushless DC motor generally wants to use the speed control that the speed can be stable at the set value without too much change when the load changes. Therefore, the motor is equipped with a hall-sensor that can induce magnetic field, which is used as the closed loop control of speed and the basis of phase sequence control. But it’s only for speed control and it’s not for positioning control.
The control principle
To make the motor rotate, the control part must be based on the location of the motor rotor detected by the Hal-sensor, and then according to the stator winding to decide to open (or close) the order of the power transistor in the Inverter, so that the current flows through the motor coil in sequence to produce forward (or reverse) rotating magnetic field, and the rotor magnet interaction, This enables the motor to rotate in sequence/reverse time. When the motor rotor rotates to the position where another set of signals are detected by the Hall-sensor, the control part turns on the next set of power transistors, so that the circulating motor can continue to rotate in the same direction until the control part decides to stop the motor rotor and turn off the power transistor (or only turn on the power transistor of the lower arm). If the rotor of the motor is reversed, the power transistor is turned on in reverse order.
Fixed magnetic field brushless motor
General brushless DC motor is a servo motor in essence, composed of synchronous motor and driver, is a variable frequency speed motor. Voltage variable speed brushless DC motor is the real sense of brushless DC motor, it is composed of stator and rotor, stator is composed of iron core, coil using “shun – inverse – shun – inverse……” The rotor consists of either a cylindrical magnet (with a shaft in the middle) or an electromagnet plus a collecting ring. This brushless DC motor can generate torque but cannot control direction. Either way, this motor is a very significant invention. When used as a DC generator, the invention can produce a dc current of continuous amplitude, thus avoiding the use of a filter capacitor, and the rotor may be permanent magnet, brushless or brushless. When used as a large motor, this motor will generate self-induction, need to use protection devices.

Asynchronous motor

Ac asynchronous motor
Ac asynchronous motor is a leading ac voltage running motor, widely used in electric fans, refrigerators, washing machines, air conditioners, hair dryers, vacuum cleaners, lampblack machines, dishwashers, electric sewing machines, food processors and other household appliances and a variety of electric tools, small electromechanical equipment.
Ac asynchronous motors are divided into induction motors and AC commutator motors. Induction motors are divided into single-phase asynchronous motors, ac and DC motors and repulsion motors.
The speed of the motor (rotor speed) is less than the speed of the rotating magnetic field, so it is called asynchronous motor. It’s basically the same as an induction motor. S = (ns – n)/ns. S is slip, NS is magnetic field speed, n is rotor speed.
Basic principles:

  • 1. When three-phase induction motor is connected to three-phase AC power supply, three-phase stator winding flows through three-phase symmetric current generated by three-phase magnetomotive force (stator rotating magnetomotive force) and generates rotating magnetic field.
  • 2. The rotating magnetic field has a relative cutting motion with the rotor conductor. According to the principle of electromagnetic induction, the rotor conductor generates an induced electromotive force and an induced current.
  • 3. According to the law of electromagnetic force, the rotor conductor carrying current is affected by the electromagnetic force in the magnetic field, forming the electromagnetic torque, driving the rotor to rotate, when the motor shaft with mechanical load, it will output mechanical energy.

Induction motor is a kind of ac motor, its load speed and the ratio of the frequency of the grid is not a constant relationship. It also varies with the size of the load. The higher the load torque, the lower the rotor speed. Induction motor includes induction motor, doubby-fed induction motor and ac commutator motor. Induction motor is the most widely used, in the case of not causing misunderstanding or confusion, generally can be called induction motor induction motor.
The stator windings of the ordinary induction motor are connected with the AC power grid, and the rotor windings do not need to be connected with other power sources. Therefore, it has the advantages of simple structure, convenient manufacture, use and maintenance, reliable operation, small quality and low cost. Asynchronous motor has high operating efficiency and better working characteristics, from no load to full load range close to constant speed operation, can meet the transmission requirements of most industrial and agricultural production machinery. Induction motor is also easy to be derived into various types of protection to meet the needs of different environmental conditions. When asynchronous motor is running, reactive excitation power must be absorbed from the grid, so that the power factor of the grid becomes bad. Therefore, to drive the ball mill, compressor and other high power, low speed of mechanical equipment, often use synchronous motor. Because the speed of the induction motor and its rotating magnetic field speed has a certain slip relationship, its speed regulation performance is poor (except ac commutator motor). It is more economical and convenient to use DC motor for transportation machinery, rolling mill, large machine tools, printing and dyeing machinery and papermaking machinery which require a wide and smooth speed range. But with the development of high power electronic devices and ac speed regulation system, the speed regulation performance and economy of induction motor suitable for wide speed regulation can be comparable with that of DC motor.
Single-phase asynchronous motor
Single-phase asynchronous motor is composed of stator, rotor, bearing, shell, end cover and so on.
The stator consists of a frame and an iron core with windings. The core is made of silicon steel sheet punching groove, and two sets of main winding (also known as running winding) and auxiliary winding (also known as starting winding) are embedded in the groove, which are separated by 90° electrical Angle in space. The main winding is connected to the AC power supply, and the auxiliary winding is connected to the centrifugal switch S or the starting capacitor and the running capacitor in series, and then connected to the power supply.
The rotor is a cage type cast aluminum rotor, which is cast into the groove of the iron core with aluminum after the iron core is overpressed, and the end ring is cast together, so that the guide bar of the rotor is short-circuited into a squirrel cage type.
Single-phase asynchronous motor is divided into single-phase resistor starting asynchronous motor, single-phase capacitor starting asynchronous motor, single-phase capacitor running asynchronous motor and single-phase double value capacitor asynchronous motor.
Three phase asynchronous motor
The structure of the three-phase asynchronous motor is similar to that of the single-phase asynchronous motor. The stator core slot is mounted with three-phase windings (there are three structures: single-layer chain type, single-layer concentric type and single-layer cross type). After the stator is connected to the three-phase AC power supply, the rotating magnetic field generated by the winding current generates the induced current in the rotor conductor, and the rotor in the interaction of the induced current and the gap rotating magnetic field produces the electromagnetic converter (namely the asynchronous converter), so that the motor rotates.
Shaded pole motor
The shaded pole motor is one of the simplest unidirectional AC motors, usually with a cage chute cast aluminum rotor. According to the stator shape structure, it can be divided into salient pole covered pole motor and hidden pole covered pole motor.
The shape of the stator core of the salient pole type shaded pole motor is a square, rectangular or circular magnetic field frame, with the magnetic poles protruding, and each magnetic pole has one or more short-circuit copper rings that play an auxiliary role, namely the shaded pole winding. The concentrated winding on the salient pole is the primary winding.
Non-salient pole type cover pole motor stator core is the same as the common core of single-phase motor, the stator winding adopts the distributed winding, the main distribution in stator slot winding, shaded pole winding don’t short circuit copper ring, but with the coarser the enameled wire wound as distributed winding (series after short circuit) embedded in the stator slot (about two-thirds of the total number of slots), a support group. The main winding and the shaded pole winding are separated by a certain Angle in space.
When the main winding of the shaded pole motor is energized, the shaded pole winding will also generate an induced current, so that the magnetic flux of the covered part of the shaded pole winding of the stator pole and the uncovered part will rotate to the direction of the covered part.
Single phase series motor
The stator of single-phase series motor is composed of prominent pole core and excitation winding, and the rotor is composed of hidden pole core, armature winding, commutator and rotating shaft. A series loop is formed between the field winding and the armature winding through a brush and a commutator.
Single-phase series motor belongs to ac and DC motor, it can use both AC power supply and DC power supply.

Synchronous motor

Synchronous motor is a common AC motor like induction motor. It is characterized by: during steady-state operation, there is a constant relationship between rotor speed and grid frequency, n = ns = 60F / P, and NS becomes synchronous speed. If the frequency of the power grid remains unchanged, the speed of the synchronous motor in the steady state is constant regardless of the size of the load. Synchronous motor is divided into synchronous generator and synchronous motor. Synchronous motors are the main AC machines in modern power plants.
Working principle
Establishment of main magnetic field: the excitation winding is connected with DC excitation current to establish the excitation magnetic field between polarity phases, that is, the main magnetic field is established.
Current carrying conductor: three-phase symmetrical armature winding acts as power winding and becomes the carrier of induced potential or induced current.
Cutting movement: the prime mover drives the rotor to rotate (input mechanical energy to the motor), the excitation magnetic field between polarities rotates with the shaft and cuts each phase winding of the stator in sequence (equivalent to the conductor of the winding cutting the excitation magnetic field in reverse).
Generation of alternating potential: due to the relative cutting movement between the armature winding and the main magnetic field, the armature winding will induce a three-phase symmetrical alternating potential whose size and direction change periodically. Through the outgoing line, AC power can be provided.
Alternation and symmetry: due to the alternating polarity of the rotating magnetic field, the polarity of the induced potential alternates; Due to the symmetry of armature winding, the three-phase symmetry of induced potential is ensured.

AC synchronous motor

AC synchronous motor is a constant speed drive motor. Its rotor speed maintains a constant proportional relationship with the power frequency. It is widely used in electronic instruments, modern office equipment, textile machinery and so on.

Permanent magnet synchronous motor

Permanent magnet synchronous motor belongs to asynchronous starting permanent magnet synchronous motor. Its magnetic field system is composed of one or more permanent magnets. Usually, the magnetic poles embedded with permanent magnets are installed in the cage rotor welded with cast aluminum or copper bars according to the required number of poles. The stator structure is similar to that of asynchronous motor.
When the stator winding is powered on, the motor starts to rotate according to the principle of asynchronous motor and accelerates to the synchronous speed, the synchronous electromagnetic torque generated by the rotor permanent magnetic field and the stator magnetic field (the electromagnetic torque generated by the rotor permanent magnetic field is combined with the reluctance torque generated by the stator magnetic field) pulls the rotor into synchronization, and the motor enters synchronous operation.
Reluctance synchronous motor reluctance synchronous motor, also known as reactive synchronous motor, is a synchronous motor that generates reluctance torque by using the unequal cross axis and direct axis reluctance of rotor. Its stator structure is similar to that of asynchronous motor, but the rotor structure is different.

Reluctance synchronous motor

Evolved from the same cage asynchronous motor, in order to enable the motor to produce asynchronous starting torque, the rotor is also equipped with cage cast aluminum winding resistance. The rotor is provided with a reaction tank corresponding to the number of stator poles (only the function of salient pole part, no excitation winding and permanent magnet) to generate reluctance synchronous torque. According to the different structures of the reaction tank on the rotor, it can be divided into internal reaction rotor, external reaction rotor and internal and external reaction rotor. Among them, the external reaction rotor reaction tank is opened to the outer circle of the rotor, so that the air gap in the direction of straight axis and quadrature axis is unequal. A groove is opened inside the inner reactive rotor to block the magnetic flux in the quadrature axis direction and increase the magnetic resistance. The internal and external reactive rotor combines the structural characteristics of the above two rotors, and the difference between the direct axis and the quadrature axis is large, so that the force energy of the motor is large. Reluctance synchronous motors are also divided into single-phase capacitor operation type, single-phase capacitor starting type, single-phase double value capacitor type and so on.

Hysteresis synchronous motor

Hysteresis synchronous motor is a synchronous motor that uses hysteresis materials to produce hysteresis torque. It is divided into inner rotor hysteresis synchronous motor, outer rotor hysteresis synchronous motor and single-phase shaded pole hysteresis synchronous motor.
The rotor structure of inner rotor hysteresis synchronous motor is hidden pole type, the appearance is a smooth cylinder, there is no winding on the rotor, but there is an annular effective layer made of hysteresis material on the outer circle of the iron core.
After the stator winding is powered on, the generated rotating magnetic field causes the hysteresis rotor to generate asynchronous torque and start rotation, and then it is pulled into the synchronous operation state by itself. When the motor operates asynchronously, the stator rotating magnetic field magnetizes the rotor repeatedly with slip frequency; During synchronous operation, the hysteresis material on the rotor is magnetized and permanent magnetic poles appear, resulting in synchronous torque. The soft starter adopts three-phase anti parallel thyristor as the voltage regulator, which is connected between the power supply and the motor stator. This circuit is like a three-phase fully controlled bridge rectifier circuit. When the soft starter is used to start the motor, the output voltage of the thyristor gradually increases and the motor gradually accelerates until the thyristor is fully connected. The motor works on the mechanical characteristics of the rated voltage to realize smooth start, reduce the starting current and avoid starting overcurrent tripping. When the motor reaches the rated speed, the starting process ends, and the soft starter automatically uses the bypass contactor to replace the thyristor that has completed the task, so as to provide the rated voltage for the normal operation of the motor, so as to reduce the heat loss of the thyristor, prolong the service life of the soft starter, improve its working efficiency, and avoid harmonic pollution in the power grid. The soft starter also provides the soft stop function. The soft stop is opposite to the soft start process. The voltage gradually decreases and the number of revolutions gradually decreases to zero to avoid the torque impact caused by free stop.

Gear motor

Reduction motor refers to the integration of reducer and motor (motor). This integrated body can also be called gear motor or gear motor. It is usually supplied in complete sets after integrated assembly by a professional reducer manufacturer. Reduction motors are widely used in iron and steel industry, machinery industry and so on. The advantage of using reduction motor is to simplify the design and save space.

  • 1. The reduction motor is manufactured in combination with international technical requirements and has high scientific and technological content.
  • 2. Space saving, reliable and durable, high overload bearing capacity, and the power can reach more than 95kw.
  • 3. Low energy consumption, superior performance, reducer efficiency of more than 95%.
  • 4. It has the advantages of low vibration, low noise and high energy saving. It is made of high-quality steel materials, steel cast iron box, and the gear surface is subjected to high-frequency heat treatment.
  • 5. After precision machining, the positioning accuracy is ensured. All these constitute the gear reduction motor of the gear transmission assembly, which is equipped with various motors, forming electromechanical integration, and completely ensuring the quality characteristics of the product.
  • 6. The product adopts the design idea of serialization and modularization, which has wide adaptability. This series of products have extremely many motor combinations, installation positions and structural schemes, and can choose any speed and various structural forms according to the actual needs.

Classification of reduction motor:

  • 1. High power gear motor;
  • 2. Coaxial helical gear reduction motor;
  • 3. Parallel shaft helical gear reduction motor;
  • 4. Spiral bevel gear reduction motor;
  • 5. YCJ series gear motor.

Reduction motors are widely used in reduction transmission mechanisms of various general mechanical equipment such as metallurgy, mining, hoisting, transportation, cement, construction, chemical industry, textile, printing and dyeing, pharmaceutical and so on.

Variable frequency motor

Frequency conversion technology actually uses the principle of motor control to control the motor through the so-called frequency converter. The motor used for such control is called variable frequency motor.
Common variable frequency motors include three-phase asynchronous motor, DC brushless motor, AC brushless motor and switched reluctance motor.
Control principle of variable frequency motor
Generally, the control strategies of variable frequency motor are: constant torque control at base speed, constant power control above base speed and ultra-high speed field weakening control.
Base speed: because the back electromotive force will be generated when the motor is running, and the size of the back electromotive force is usually directly proportional to the speed. Therefore, when the motor runs to a certain speed, because the back EMF is the same as the applied voltage, the speed at this time is called the base speed.
Constant torque control: the motor carries out constant torque control at base speed. At this time, the back electromotive force E of the motor is directly proportional to the speed of the motor. In addition, the output power of the motor is directly proportional to the product of the torque and speed of the motor, so the motor power is directly proportional to the speed at this time.
Constant power control: when the motor exceeds the base speed, the back EMF of the motor is basically kept constant by adjusting the motor excitation current, so as to improve the speed of the motor. At this time, the output power of the motor remains basically constant, but the motor torque decreases in inverse proportion to the speed.
Field weakening control: when the motor speed exceeds a certain value, the excitation current is quite small and can hardly be adjusted. At this time, it enters the field weakening control stage.
The speed regulation and control of motor is one of the basic technologies of various industrial and agricultural machinery, office and livelihood Electrical equipment. With the amazing development of power electronics technology and microelectronics technology, the AC speed regulation mode of “special frequency conversion induction motor + frequency converter” is guiding a new change to replace the traditional speed regulation mode in the field of speed regulation with its excellent performance and economy. The Gospel it brings to all walks of life is that it greatly improves the degree of mechanical automation and production efficiency, saves energy, improves the product qualification rate and product quality, correspondingly improves the capacity of power supply system, miniaturizes equipment and increases comfort. It is replacing the traditional mechanical speed regulation and DC speed regulation schemes at a very fast speed.
Due to the particularity of variable frequency power supply and the requirements of the system for high-speed or low-speed operation and speed dynamic response, strict requirements are put forward for the motor as the main power body, which brings new topics in electromagnetism, structure and insulation to the motor.
Application of variable frequency motor
Variable frequency speed regulation has become the mainstream speed regulation scheme, which can be widely used in all walks of life.
Especially with the increasingly wide application of frequency converter in the field of industrial control, the use of frequency conversion motor is becoming more and more widely. It can be said that because of the advantages of frequency conversion motor over ordinary motor in frequency conversion control, it is not difficult for us to see the figure of frequency conversion motor where frequency converter is used.

Linear motor

The traditional feed transmission mode of “rotating motor + ball screw” on the machine tool is difficult to make a breakthrough in the aspects of feed speed, acceleration and rapid positioning accuracy due to the limitation of its own structure. It has been unable to meet the higher requirements of ultra-high speed cutting and ultra precision machining on the servo performance of the machine tool feed system. Linear motor directly converts electric energy into linear motion mechanical energy without any transmission device of intermediate conversion mechanism. It has the advantages of large starting thrust, high transmission stiffness, fast dynamic response, high positioning accuracy and unlimited stroke length. In the feed system of the machine tool, the biggest difference between the direct drive of the linear motor and the transmission of the original rotating motor is that the mechanical transmission link from the motor to the workbench (carriage) is cancelled, and the length of the feed transmission chain of the machine tool is shortened to zero. Therefore, this transmission mode is also called “zero transmission”. It is precisely because of this “zero transmission” mode that brings the performance indexes and advantages that the original rotating motor driving mode can not achieve.
1. High speed response
Because some mechanical transmission parts with large response time constant (such as lead screw) are directly cancelled in the system, the dynamic response performance of the whole closed-loop control system is greatly improved and the response is extremely sensitive and fast.
2. Precision
The linear drive system eliminates the transmission clearance and error caused by mechanical mechanisms such as lead screw, and reduces the tracking error caused by the lag of the transmission system during interpolation movement. Through the linear position detection feedback control, the positioning accuracy of the machine tool can be greatly improved.
3. High dynamic stiffness due to the “direct drive”, the motion lag caused by the elastic deformation, friction and wear and reverse clearance of the intermediate transmission link during startup, speed change and reversing is avoided, and the transmission stiffness is also improved.
4. Fast speed and short acceleration and deceleration process
Since linear motors were first mainly used in maglev trains (up to 500km / h), there is certainly no problem to meet the maximum feed speed of ultra-high speed cutting (up to 60 ~ 100M / min or higher) when they are used in the feed drive of machine tools. Due to the high-speed response of the above “zero transmission”, the acceleration and deceleration process is greatly shortened. In order to achieve instant high speed when starting and instant quasi stop when running at high speed. Higher acceleration can be obtained, generally up to 2 ~ 10g (g = 9.8m / S2), while the maximum acceleration of ball screw transmission is generally only 0.1 ~ 0.5g.
5. The stroke length is not limited

On the guide rail, the stroke length can be extended infinitely by series linear motor.
6. Quiet movement and low noise

Since the mechanical friction of transmission lead screw and other components is eliminated, and the guide rail can adopt rolling guide rail or magnetic pad suspension guide rail (without mechanical contact), the noise during its movement will be greatly reduced.
7. High efficiency

Because there is no intermediate transmission link, the energy loss during mechanical friction is eliminated, and the transmission efficiency is greatly improved.

Basic structure and composition of motor

  • 1. The basic components of the motor are stator, rotor and other accessories. The stationary part is called the stator, which generates a magnetic field and acts as the mechanical support of the motor. The rotating part is called rotor, and its function is to induce electric potential to realize energy conversion.
  • 2. There is a certain gap between the stationary part and the rotating part, which is called air gap. Air gap is a part of the magnetic circuit of the motor and an important factor determining the quality of the motor. The size of the air gap determines the magnetic flux. If the air gap is large, there will be more magnetic flux leakage, which will increase the excitation current and reduce the power factor. If the air gap is too small, it is easy to sweep through the stator hole, and the rotor core and stator core will collide during operation. Therefore, it is necessary to control the air gap at a reasonable value.
  • 3. Generally speaking, the air gap of small and medium-sized three-phase asynchronous motors is 0.2 ~ 1.0mm, and that of large three-phase asynchronous motors is 1.0 ~ 1.5mm.

Basic structure and composition of three-phase asynchronous motor

1. There are many types of motors, which can be simply divided into AC motor and DC motor. AC motor is divided into synchronous motor and asynchronous motor. Asynchronous motor can also be divided into single-phase and three-phase. Here we mainly talk about the basic structure and composition of three-phase asynchronous motor.
2. Three phase asynchronous motor is usually used to drive various production machines. It is mainly composed of stator and rotor. Due to different rotor structures, it can be divided into three-phase cage motor and winding motor.

  • (1) The stator of three-phase asynchronous motor is mainly composed of stator core, stator winding and base.
  • (2) The function of stator is to generate rotating magnetic field after introducing three-phase symmetrical AC to drive the rotor to rotate. The stator core is a part of the magnetic circuit of the motor. Silicon steel sheet with thickness of -0.35 ~ 0.5mm can be folded into a cylinder and installed in the frame.
  • (3) The stator winding is the circuit part of the motor, which is divided into single layer and double layer and embedded in the inner circular groove of the stator core. The small asynchronous motor adopts single-layer winding, and the large and medium asynchronous motor adopts double-layer winding.
  • (4) The stator winding of the motor is usually wound by enamelled wire, which is divided into three groups, which are distributed in the stator core slot (with an interval of 1200 °) to form a symmetrical three-phase winding. The three-phase winding has six outputs.
  • (5) The frame is the shell and support of the motor, which is used to fix and support the stator core and end cover.
  • (6) When the phase sequence of the three-phase AC input to the stator of the three-phase asynchronous motor changes, the rotation direction of the motor rotor also changes due to the change of the direction of the stator rotating magnetic field.

3. The rotor of three-phase asynchronous motor is mainly composed of rotor core, rotor winding and rotating shaft. The function of rotor is to generate induced electromotive force and induced current, form electromagnetic torque, realize the conversion of electromechanical energy, and drive the load machinery to rotate.

  • (1) The rotor winding structure of three-phase asynchronous motor is different, which can be divided into cage rotor and wound rotor. The cage rotor winding is composed of bare conductor bars (copper bars or aluminum bars) embedded in the rotor core slot. After removing the rotor core, the whole winding looks like a cage, so it is named.
  • (2) The wound rotor winding is similar to the stator winding and consists of three-phase symmetrical windings embedded in the rotor core slot. The windings are connected in a star shape. The ends of the three windings are connected together. The three heads are respectively connected with three copper collector rings fixed on the rotating shaft and insulated from each other. They are connected to the variable resistance of the external circuit through the brush for starting or speed regulation.
  • (3) The rotor core, stator and air gap together constitute the magnetic circuit of the motor. The rotor core is also laminated by silicon steel sheets and pressed on the rotating shaft.

The basic structure and composition of the motor are basically the same as those of the three-phase motor. The three-phase motor was originally derived from the motor. So far, the development of the motor has achieved a lot of work that can not be achieved by manpower, greatly reducing people’s attention; Labor consumption, with the upgrading of motor technology, the energy-saving and efficient technology of motor is gradually rising in the market.

Inspection of motor

Inspection method before starting:

  • 1. For new or long-term out of service motors, the insulation resistance between windings and winding to ground shall be checked before use. Generally, 500V insulation resistance meter is used for motors below 500V; 1000V insulation resistance meter for 500-1000v motor; 2500V insulation resistance meter shall be used for motors above 1000V. The insulation resistance shall not be less than 1m Ω per kV working voltage and shall be measured when the motor is cooled.
  • 2. Check whether the appearance of the motor has cracks, whether all fastening screws and parts are complete, and whether the fixation of the motor is good.
  • 3. Check whether the motor transmission mechanism works reliably.
  • 4. According to the data shown on the nameplate, whether the voltage, power, frequency, connection, speed, etc. are consistent with the power supply and load.
  • 5. Check whether the ventilation and bearing lubrication of the motor are normal.
  • 6. Pull the motor shaft to check whether the rotor can rotate freely and whether there is noise during rotation.
  • 7. Check the brush assembly of the motor, whether the brush lifting mechanism is flexible and whether the position of the brush lifting handle is correct.
  • 8. Check whether the motor grounding device is reliable.

Main purpose of motor

1. Servo motor
Servo motor is widely used in various control systems. It can convert the input voltage signal into the mechanical output on the motor shaft and drag the controlled components to achieve the purpose of control.
Servo motors can be divided into DC and ac. the earliest servo motors were general DC motors. When the control accuracy was not high, general DC motors were used as servo motors. In terms of structure, DC servo motor is a low-power DC motor. Its excitation mostly adopts armature control and magnetic field control, but armature control is usually used.
2. Stepping motor
Stepper motor is mainly used in the field of NC machine tool manufacturing. Because stepper motor does not need a / D conversion and can directly convert digital pulse signal into angular displacement, it has always been considered as the most ideal actuator of NC machine tool.
In addition to its application in CNC machine tools, stepper motors can also be used in other machines, such as motors in automatic feeders, motors in general floppy disk drives, printers and plotters.
3. Torque motor
Torque motor has the characteristics of low speed and strong torque. AC torque motor is often used in textile industry. Its working principle and structure are the same as that of single-phase asynchronous motor.
4. Switched reluctance motor
Switched reluctance motor is a new type of speed regulating motor, which has extremely simple and firm structure, low cost and excellent speed regulating performance. It is a strong competitor of traditional control motor and has strong market potential.
5. Brushless DC motor
Brushless DC motor has good linearity of mechanical characteristics and regulation characteristics, wide speed regulation range, long service life, convenient maintenance, low noise and no series of problems caused by brush. Therefore, this motor has great application in control system.
6. DC motor
DC motor has the advantages of good speed regulation performance, easy starting and load starting, so DC motor is still widely used, especially after the emergence of thyristor DC power supply.
7. Asynchronous motor
Asynchronous motor has the advantages of simple structure, convenient manufacture, use and maintenance, reliable operation, low quality and low cost. Asynchronous motors are widely used to drive most industrial and agricultural production machinery, such as machine tools, water pumps, blowers, compressors, hoisting equipment, mining machinery, light industrial machinery, agricultural and sideline products processing machinery, as well as household appliances and medical devices.
It is widely used in household appliances, such as electric fans, refrigerators, air conditioners, vacuum cleaners, etc.
8. Synchronous motor
Synchronous motors are mainly used in large machinery, such as blowers, water pumps, ball mills, compressors, rolling mills, small and micro instruments and equipment, or as control components. The three-phase synchronous motor is its main body. In addition, it can also be used as a condenser to transmit inductive or capacitive reactive power to the power grid.

Maintenance method of motor

Motor maintenance process of professional motor maintenance center: cleaning stator and rotor – replacing carbon brush or other parts – vacuum class F pressure paint dipping – drying – dynamic balance calibration.

  • 1. The operating environment shall be kept dry, the motor surface shall be kept clean, and the air inlet shall not be obstructed by dust, fiber, etc.
  • 2. When the thermal protection of the motor acts continuously, find out whether the fault is from the motor or overload or the setting value of the protection device is too low. After the fault is eliminated, it can be put into operation.
  • 3. Ensure good lubrication of the motor during operation. Generally, when the motor runs for about 5000 hours, the lubricating grease shall be supplemented or replaced. When the bearing is overheated or the lubrication is deteriorated during operation, the hydraulic pressure shall change the lubricating grease in time. When replacing the grease, remove the old lubricating oil and clean the oil groove of the bearing and bearing cover with gasoline, and then fill 1 / 2 (for 2 poles) and 2 / 3 (for 4, 6 and 8 poles) of the cavity between the inner and outer rings of the bearing with zl-3 lithium grease.
  • 4. When the service life of the bearing ends, the vibration and noise of the motor will increase significantly. Check that the radial clearance of the bearing reaches the following values, that is, the bearing shall be replaced.
  • 5. When disassembling the motor, take out the rotor from the shaft extension end or non extension end. If it is not necessary to remove the fan, it is more convenient to take out the rotor from the non shaft extension end. When taking out the rotor from the stator, prevent damage to the stator winding or insulation.
  • 6. When replacing the winding, the form, size, number of turns, wire gauge, etc. of the original winding must be recorded. When these data are lost, they should be obtained from the manufacturer. Changing the original design winding at will often worsens one or more performance of the motor, or even can not be used.

Motor protector

The function of motor protector is to provide comprehensive protection for the motor. It is a device to alarm or protect the motor in case of overload, phase loss, locked rotor, short circuit, overvoltage, undervoltage, electric leakage, three-phase imbalance, overheating, bearing wear and eccentric stator and rotor.

General knowledge of motor protection

20210802103136 46244 - What is a motor
Physical drawing of motor
1. The motor is easier to burn than in the past: due to the continuous development of insulation technology, it is required to increase output and reduce volume in the design of the motor, so that the thermal capacity of the new motor is smaller and smaller, and the overload capacity is weaker and weaker; Moreover, due to the improvement of production automation, the motor is required to run in a variety of ways such as frequent starting, braking, forward and reverse rotation and variable load, which puts forward higher requirements for the motor protection device. In addition, motors are widely used and often work in extremely harsh environments, such as humid, high temperature, dusty, corrosive and other occasions. All these make the motor easier to be damaged, especially overload, short circuit, phase loss, bore sweeping and other faults with the highest frequency.
2. The protection effect of the traditional protection device is not ideal: the traditional motor protection device is mainly thermal relay, but the thermal relay has low sensitivity, large error, poor stability and unreliable protection. In fact, although thermal relays are installed in many equipment, the phenomenon of motor damage affecting normal production is still common.
3. Development status of motor protection: the motor protector has developed from mechanical type to electronic and intelligent type. It can directly display the current, voltage, temperature and other parameters of the motor. It has high sensitivity, high reliability, multiple functions and convenient debugging. After the protection action, the types of faults are obvious, which not only reduces the damage of the motor, but also greatly facilitates the judgment of faults, It is conducive to the troubleshooting of the production site and shorten the recovery time. In addition, the motor eccentricity detection technology using the motor air gap magnetic field makes it possible to monitor the motor wear status online. The curve shows the change trend of the motor eccentricity, which can early detect the bearing wear and faults such as walking in the inner circle and outer circle, so as to achieve early detection and early treatment and avoid the occurrence of bore sweeping accidents.
3. Selection principle of protector: reasonably select the motor protection device, which can not only give full play to the overload capacity of the motor, but also avoid damage, so as to improve the reliability of the electric drive system and the continuity of production. The specific function selection shall comprehensively consider the value of the motor itself, load type, service environment, the importance of the main equipment of the motor, whether the motor out of operation has a serious impact on the production system and other factors, and strive to be economical and reasonable.
4. Ideal motor protector: the ideal motor protector is neither the most functional nor the so-called most advanced, but should meet the actual needs of the site, achieve the unity of economy and reliability, and have a high performance price ratio. The types and functions of protectors shall be reasonably selected according to the actual situation of the site. At the same time, the simple and convenient installation, adjustment and use of protectors shall be considered. More importantly, high-quality protectors shall be selected.

Selection of protector

Basic principles of model selection:
There is no unified standard for motor protection products in the market, and there are various models and specifications. In order to meet the different use needs of users, manufacturers have derived many series of products with a wide variety, which brings a lot of inconvenience to the selection of users; When selecting the type, the user shall fully consider the actual needs of motor protection and reasonably select the protection function and protection mode, so as to achieve good protection effect, improve the operation reliability of equipment, reduce unplanned shutdown and reduce accident losses.
The method of model selection:
1. Conditions related to model selection

  • 1) Motor parameters: first understand the specification and model, functional characteristics, protection type, rated voltage, rated current, rated power, power frequency, insulation grade, etc. of the motor. These contents can basically provide a reference basis for users to correctly select protectors.
  • 2) Environmental conditions: mainly refer to normal temperature, high temperature, high cold, corrosion, vibration, wind and sand, altitude, electromagnetic pollution, etc.
  • 3) Purpose of motor: it mainly refers to the required characteristics of driving mechanical equipment, such as fan, water pump, air compressor, lathe, oilfield pumping unit and other mechanical characteristics of different loads.
  • 4) Control mode: the control modes include manual, automatic, local control, remote control, independent operation of single machine, centralized control of production line, etc. The starting modes include direct, step-down, star angle, frequency sensitive rheostat, frequency converter, soft start, etc.
  • 5) Other aspects: monitoring and management of on-site production by users, severity of impact of abnormal shutdown on production, etc.

There are many factors related to the selection of protector, such as installation location, power supply, distribution system, etc; Also consider whether to configure protection for newly purchased motors, upgrade motor protection, or improve accident motor protection; The difficulty of changing the motor protection mode and its impact on production shall also be considered; The selection and adjustment of protector shall be comprehensively considered according to the actual working conditions on site.
2. Common types of motor protectors

  • 1) Thermal relay: Ordinary small capacity AC motor, with good working conditions and no severe working conditions such as frequent startup; Due to poor accuracy and reliability, it is not recommended.
  • 2) Electronic type: detect the three-phase current value. The setting current value adopts potentiometer or code pulling switch. The circuit generally adopts analog type and adopts inverse time limit or fixed time limit working characteristics. The protection functions include overload, phase loss, locked rotor, etc. the fault type is displayed by indicator light, and the operating power is displayed by nixie tube.
  • 3) Intelligent type: detect the three-phase current value. The protector uses single chip microcomputer to realize the intelligent comprehensive protection of motor, integrating protection, measurement, communication and display. The setting current is set digitally and operated through the buttons on the operation panel. The user can modify and set various parameters on site according to the specific situation of the motor; It adopts nixie tube as the display window or large screen LCD display, which can support a variety of communication protocols, such as modbus, PROFIBUS, etc. with relatively high price, it is used in more important occasions; High voltage motor protection adopts intelligent protection device.
  • 4) Thermal protection type: the thermal element is embedded in the motor and protected according to the temperature of the motor winding, with good protection effect; However, when the motor capacity is large, it should be used together with the current monitoring type to avoid the motor winding damage due to the hysteresis of the temperature measuring element when the temperature rises sharply when the motor is locked.
  • 5) Magnetic field temperature detection type: the magnetic field detection coil and temperature measuring element are embedded in the motor to protect according to the change of rotating magnetic field and temperature inside the motor. The main functions include overload, locked rotor, phase loss, overheating protection and wear monitoring. The protection function is perfect. The disadvantage is that the magnetic field detection coil and temperature sensor need to be installed inside the motor.

3. Selection of protector type

  • 1) For the single machine independent operation motor with low requirements for working conditions, simple operation control and little impact of shutdown on production, the ordinary protector can be selected. Because the ordinary protector has the advantages of simple structure, convenient installation, wiring and replacement on site, simple operation and high cost performance.
  • 2) For motors with poor working conditions and high reliability requirements, especially those involving automatic production lines, medium and high-grade intelligent protectors with complete functions shall be selected.
  • 3) For the explosion-proof motor, the eccentricity caused by bearing wear may lead to high temperature friction at the explosion-proof gap and explosion hazard. The wear condition monitoring function should be selected. For special equipment such as high-capacity high-pressure submersible pump, due to the difficulty of inspection and maintenance, the wear condition monitoring function should also be selected, and the bearing temperature should be monitored to avoid significant economic losses caused by chamber sweeping accident.
  • 4) For protectors used in places with explosion-proof requirements, corresponding explosion-proof protectors shall be selected according to the specific requirements of the application site to avoid safety accidents.

Source: China Permanent Magnet Manufacturer – www.rizinia.com

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