What are the characteristics of motor step down and inverter start 20

Step-down start: Step-down start is used to reduce the starting current, but at the same time the starting torque of the motor will be reduced, so it is only suitable for occasions with low requirements for starting, no load or light load.

1) Y start: The motor is actually used for stator winding connection, the equipment is simple, can be started frequently, and is widely used.

2) Stator loop string resistance step-down start: the resistor is short-circuited during the start-up process, the resistance loss is large, and the resistance capacity limit can not be used frequently.

3) Autotransformer step-down start: the stator circuit is connected to the transformer to start, and the transformer is cut off after starting, which should not be started frequently, but the start is more stable, the equipment is simpler, and the application is more extensive.

4) Extended edge triangle start: the extension of y start, but the control is very cumbersome, and there are special requirements when the motor is manufactured, so it is rarely used.

5) Soft start: the use of semiconductor rectifier and inverter technology to reduce the input voltage of the motor, gradually increase to the rated voltage, the start is very smooth, the control is very convenient, but the highest is higher, with the rapid development of semiconductor technology such as high-power rectifier components, soft start has been widely used.

Frequency conversion start: The frequency converter is the motor control device with the highest technical content, the most complete control function and the best control effect in the field of modern motor control, which adjusts the speed and torque of the motor by changing the frequency of the power grid. Because it involves power electronics technology and microcomputer technology, the cost is high and the requirements for maintenance technicians are also high, so it is mainly used in the field that requires speed regulation and high requirements for speed control.

1. Current, the current impact is large when the step-down starts, and gradually decreases later. There is another large current impulse during the rotation, which then gradually decreases until the end of a smooth start-up. The variable frequency starting current is relatively stable and has no impact.

2. Mechanical, step-down start has a great impact on the equipment, which increases the failure rate of the equipment. The inverter has no impact on the equipment, reducing failures. 3. Torque, the starting torque of step-down is small.

The frequency conversion start mode can be set, and the torque is larger. 4. The number of times, step-down start (auto-coupling step-down start-up cabinet) can not be started for a long time or multiple times in a row, otherwise the cabinet will be burned (except for star triangle start). It's fine when the inverter starts.

5. The inverter can make the motor run at any speed below the rated speed. Buck start-up is not a no-no. 6. The inverter drags the fan and water pump, and adjusts the air volume and water volume (wind pressure, water pressure) by adjusting the speed to save electricity.

Start the pressure reduction and drag the fan and water pump, and adjust the air volume and water volume (wind pressure, water pressure) by adjusting the damper and water valve. 7In short, the inverter is much stronger than the step-down start, but it is more expensive when you buy it.

Basically, the frequency conversion start is to reduce the frequency of the power supply at the same time, the voltage is also reduced, but the starting torque is slightly larger than the ordinary step-down start.

Step-down start is difficult to start with heavy load, while variable frequency start can, which is the biggest difference, and the common point is that the starting current is relatively small.

Hello dear! The step-down start mode of asynchronous motor is as follows: The commonly used methods for step-down start of three-phase cage asynchronous motor are resistance step-down start, auto-transformer step-down start, Y- start, and step-down start.

1.The rotation speed of the rotor of the three-phase asynchronous motor is lower than the rotation speed of the rotating magnetic field, and the rotor winding generates electromotive force and current due to the relative motion between it and the magnetic field, and interacts with the magnetic field to generate electromagnetic torque to achieve energy conversion. 2.

Compared with single-phase asynchronous motors, three-phase asynchronous motors have good running performance and can save various materials. According to the different rotor structures, three-phase asynchronous motors can be divided into cage type and winding type. The asynchronous motor of the cage rotor has a simple structure, reliable operation, light weight and low cost, and has been widely used, but its main disadvantage is that it is difficult to regulate the speed.

The rotor of the wound three-phase asynchronous motor, like the stator, is also provided with three-phase windings and is connected to an external rheostat through slip rings and brushes. Adjusting the rheostat resistance can improve the starting performance of the motor and adjust the rotational speed of the motor. 3.

Principle: When a symmetrical three-phase alternating current is introduced into the three-phase stator winding, a rotating magnetic field is generated that rotates clockwise along the inner circular space of the stator and rotor at a synchronous speed n1. Since the rotating magnetic field rotates at n1 rotational speed, the rotor conductor is stationary at the beginning, so the rotor conductor will cut the stator rotating magnetic field and generate an induced electromotive force (the direction of the induced electromotive force is determined by the right-hand rule).

Since the two ends of the rotor conductor are shorted by short-circuit rings, under the action of induced electromotive force, the induced current in the rotor conductor will be basically consistent with the direction of the induced electromotive force. The current-carrying conductor of the rotor is subjected to an electromagnetic force in the stator magnetic field (the direction of the force is determined by the left-hand rule). The electromagnetic force generates an electromagnetic torque on the rotor shaft, which drives the rotor to rotate in the direction of the rotating magnetic field.

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There are three methods of motor step-down start: direct, step-down, and frequency conversion start.

1) Direct start is full voltage start.

2) Step-down start-up is to reduce the start-up voltage to limit the start-up current.

3) Frequency conversion start is to change the frequency of the power supply to limit the starting current, and the specific principle is determined according to the requirements of the site, and the specific starting method is achieved in different ways.

Step-down start: The starting current of the motor is approximately proportional to the voltage of the stator, so the method of reducing the stator voltage should be used to limit the starting current, that is, the step-down start. For the occasion that the direct starting impulse current is too large and can not be beared, the decompression start is usually adopted, at this time, the starting torque decreases, and the starting current also decreases, which is only suitable for the occasion that the starting current must be reduced and the starting torque is not high.

Common step-down starting methods: stator string resistance step-down start, Y-δ start control line, extended triangle start, soft start and autotransformer step-down start.

The commonly used step-down starting methods for three-phase asynchronous motors are: stator string resistance (or reactor) step-down start, star-delta (y-one) step-down start, autotransformer step-down start and extended triangle step-down start.

When the stator of the three-phase asynchronous motor is connected in series with the starting resistor, the starting voltage of the stator winding is reduced due to the voltage division of the starting resistor, and the resistor is shorted after the start is over, so that the motor can operate normally under the rated voltage, and the starting current can be reduced.

This starting method is not limited by the wiring form of the motor, the equipment is simple and economical, and it is widely used in small and medium-sized production machinery.

During normal operation, the stator winding is connected to the three-phase asynchronous motor running in a triangle, and the star-delta step-down starting mode can be adopted. When starting, the voltage of each phase winding drops to the normal working voltage, the starting current drops, the motor starts to rotate, when the speed is close to the rated speed, the motor stator winding is reconnected into a triangle, and the motor enters the normal operation state.

The starting method of using the starting equipment to appropriately reduce the power supply voltage and add it to the stator winding of the motor to start to reduce the starting current, and then restore the voltage to the rated value after the motor speed increases is called step-down start.

Resistance step-down start, resistance loss is large, can not be started frequently, less used.

Autotransformer step-down start, the starting current is proportional to the voltage square, and it is more used, and it is not suitable for frequent start-up.

Y- starting, a motor used for stator winding connection, the equipment is simple, can be started frequently, and is often used.

Hello! The high-power motor should take the step-down start reason to reduce the voltage by using the starting equipment, and then add it to the electric Shixukai machine, when the speed of the electric engine rises to a certain value, and then transfer to the rated voltage to run. Although this method can reduce the starting current, the torque of the motor is proportional to the square of the voltage, and the starting torque of the motor is also reduced, so it is only suitable for the no-load or light-load starting occasion of the cage motor.

The advantage of direct start of the asynchronous motor is that the equipment is simple and easy to operate.

The disadvantage is that the starting current is large, and the large starting current will cause the voltage to drop too much and affect the normal operation of the motor itself and other electrical equipment on the same line.

When the power supply capacity is large enough and the voltage drop is within the allowable range, the direct start method should be used as much as possible.

The advantage of step-down start-up is that the start-up current is small. The disadvantage is that the starting torque is also greatly reduced, and the investment in equipment needs to be increased, and the operation is more complicated. It is suitable for the start of the motor under the condition of relatively small power supply capacity and no load and light load of the motor.

Direct start of asynchronous motor: the starting current is generally 4 7 times of the rated current. Harm:

The start of the high-power motor will have an impact on the power grid, and the torque force of the direct full-voltage start at the moment of starting is very large, which will damage the internal of the motor (such as the heating of the motor winding). The advantage is that it is very convenient.

Advantages of buck starting: There will be no disadvantage of direct starting. There is a gentle slope time for starting, which will not cause relay protection malfunction.

To be divided into cage asynchronous motor and wound asynchronous motor two situations to discuss, generally mainly use cage asynchronous motor.

For cage type asynchronous motors.

1.Direct start: The starting current is very large, which can easily cause the motor to overheat2Stator string resistance or reactance decompression starts.

3.Autotransformer decompression start.

4.Star-triangle decompression start.

Among them, the starting method can reduce the starting current, but the starting torque will also be reduced, I hope it will help you.

1. When the motor starts, the machine cannot withstand the impact torque of full-pressure starting;

2. When the motor starts, its terminal voltage cannot meet the requirements of the specification.

The use of autotransformer multi-tap decompression, can not only adapt to the needs of different load starting, but also can get a larger starting torque, is a kind of decompression starting method often used to start a larger capacity motor.

Its biggest advantage is that the starting torque is larger, when its winding tap is at 80%, the starting torque can reach 64% when starting directly. And the starting torque can be adjusted by tapping. It is still widely used today.

If the high-power motor is started directly (i.e., full voltage), its starting current can reach 4-7 times of the rated current, excessive starting current will cause the motor to overheat, affect the life of the motor, and at the same time, the motor winding will be deformed under the action of electric power, which may cause a short circuit and burn out the motor, and will also cause the grid voltage to drop significantly and affect the normal operation of other loads on the same power grid. Therefore, the high-power motor should be started with a step-down to limit the starting current.

Resistance buck or reactance buck starts. The resistor or reactance is connected in series in the stator circuit, so that the voltage is reduced, and the starting current and starting torque of the motor are also reduced accordingly, which is suitable for light load or no-load starting.

Autotransformer step-down start. The multi-tap decompression of the autotransformer is used to reduce the voltage of the motor at start-up, and the transformer is cut off after start-up, so that the motor runs under the rated voltage, which is suitable for ordinary cage motors.

Star-delta (y-) buck starts. For the three-phase cage motor with the stator winding connected into a triangle ( ) during normal operation, the step-down start mode of star-delta (y-) conversion can be adopted. When starting, first connect the stator winding of the motor into a star (Y), so that the voltage of each phase winding is reduced to one-third of the root number of the power supply voltage, and then change the stator winding to a triangle ( ) after the motor is started, the motor can operate normally under the rated voltage.