Suzhou Shouxin Motor Co., Ltd. tells you how to answer 14 frequently asked questions from customers

September 22, 2022

After contacting many customers who purchased motors, I collected some questions and related answers from customers. Maybe you will also encounter such confusion when using the motor or replacing the motor. There are several key words when buying a motor, common motor, aluminum shell motor, variable frequency motor, three-phase asynchronous motor, vertical installation, horizontal installation, motor power, voltage, DC motor, AC motor, etc. What you need to know when purchasing .

1. Why is the leakage circuit breaker easy to trip when using the inverter?

This is because the output waveform of the inverter contains high-order harmonics, and the motor and the cable between the inverter and the motor will generate leakage current, which is much larger than that when the motor is driven by power frequency, so this phenomenon occurs.

The leakage current on the output side of the inverter operation is about three times that of the power frequency operation. In addition to the leakage current of the motor, the operating current of the leakage protector should be greater than 10 times the leakage current at the power frequency.

2. I want to do a motor frequency conversion speed regulation experiment. Can ordinary motors realize frequency conversion speed regulation? Or do I have to buy an inverter motor?

To do the motor frequency conversion speed regulation experiment, use an ordinary AC motor.

The DC motor can also realize frequency conversion, such as the current DC frequency conversion air conditioner: it converts the power frequency AC power into DC power supply and sends it to the power module. The module is controlled by the control signal sent by the microcomputer. The controlled DC power is sent to the DC motor of the compressor to control the displacement of the compressor, so as to realize "frequency conversion speed regulation".

3. What kind of motor is an AC variable frequency motor?

To put it simply, frequency conversion technology is used in the control of AC motors. AC variable frequency motor is actually a motor that adjusts the speed of the AC frequency. The frequency of the AC frequency needs to be adjusted by the inverter, and the motor itself will not change the frequency. Inverter motor use.


4. Can the inverter single-phase 220v change into three-phase 380v?

is not possible. The inverter itself cannot boost, let alone change from single-phase 220v to three-phase 380v. This is theoretically possible, using a transformer to step up the single-phase 220V to 380V, and then convert the single-phase 380V to three-phase 380V.

5 The belt driven by the high-power motor has a reducer connected to the motor. What is the role of the reducer here?

The purpose of the reducer can be briefly summarized:

Decelerate the speed and increase the output torque at the same time. The torque output ratio is multiplied by the motor output by the speed reducer, but be careful not to exceed the rated torque of the speed reducer.

Deceleration reduces the inertia of the load at the same time, and the reduction of inertia is the square of the reduction ratio. You can look at the general motor has an inertia data.

6. Answer the reasons for the slow speed of the motor when starting?

If only the speed is slow when starting, it is normal after starting. It may be that the starting capacitor does not match, or the motor design is like this (according to the site design), or the starting time is too long due to factors such as excessive load resistance.

If the speed is still slow after starting, the problem may be insufficient voltage, mismatched capacitors, large rotation resistance, etc.


7. How to choose the brushes of the rotor collector ring of the wound asynchronous motor?

It is mainly determined according to whether the working conditions of the brush meet the current density (A/cm2) and the linear velocity (m/s) of the peripheral edge of the collector ring. Determine the formula:

① Brush current carrying capacity (A) = brush current density (A/cm2) × brush width L (cm) × brush thickness b (cm) ≥ motor rotor rated current (A);

② Linear speed of the peripheral edge of the collector ring (m/s) = rated speed of the motor (r/m)/60 (s) × the circumference of the collector ring (m) ≤ the specified range for brushes (m/s) .

The commonly used brushes are non-ink brushes, electrochemical graphite brushes and metal graphite brushes. In use, attention should be paid to frequently check the brush activity, brush pressure and degree of wear. The brush should be able to move up and down freely in the brush holder without jamming. When the brush is stuck, smooth both sides of the brush on the emery cloth. The pressure of the brush should be adjusted appropriately according to the type and model of the brush. At present, most of the brush compression springs attached to the brush holder are tension and compression springs, and their pressure gradually decreases with the wear of the brush. Therefore, during the operation of the motor, the brush pressure should be adjusted at any time.


8. The 60HZ motor is used on the 50HZ power supply. What should I pay attention to?

This is because the current frequency of the motor is lower than the design frequency. To reduce the no-load back EMF generated during the rotation and increase the no-load current, which will cause damage to the motor, the no-load voltage is required to be reduced.

In the variable frequency speed regulation technology, the frequency of the motor and the voltage of the stator are changed at the same time. That is, when the frequency drops, the voltage also drops at the same time, so that the motor will not be over-current, and the ideal operating effect will be obtained.


9. Why should an output reactor be added to the output end of the inverter, and what is its function?

An output reactor is added at the output end of the inverter to increase the wire distance from the inverter to the motor. The output reactor can effectively suppress the instantaneous high voltage generated when the inverter's IGBT switches on and off, and reduce the adverse effects of this voltage on cable insulation and motor.

The main function of the reactor is to limit the capacitive charging current of the motor connection cable and limit the voltage rise rate on the motor winding to within 540V/μs, and it is also used to passivate the output voltage (switching frequency) of the inverter. to reduce the disturbance and impact of power components (such as IGBTs) in the inverter.

10. Can AC servo motors be controlled by inverters?

Because the performance and function of the inverter and the servo are different, and the applications are not quite the same, it is not possible.

In the occasions of speed control and torque control, the general-purpose inverters are not very demanding, and there are also inverters that add position feedback signals to the upper position to form a closed-loop frequency conversion for position control, and the accuracy and response are not high. Now some frequency converters also accept the pulse train signal to control the speed, but it seems that they cannot directly control the position.

In the occasions with strict position control requirements, it can only be realized by servo, and the response speed of servo is much higher than that of frequency conversion. In almost all cases, it can be replaced by servo.

The key is two points: one is that the price of servo is much higher than that of frequency conversion, and the other is the reason for power: the largest frequency conversion can achieve hundreds of KW, or even higher, and the largest servo is tens of KW. The basic concept of servo is accurate, precise and fast positioning. Frequency conversion is a necessary internal link of servo control, and there is also frequency conversion in servo drives (stepless speed regulation is required).

11. Can the speed regulating motor be started frequently?

The speed-regulated motor can be started frequently. The motors used for debugging in our company are all speed-regulated motors, which are often started frequently without any problems. However, it is of course best to minimize frequent startups. No matter how many times the motor is started frequently, it will damage the motor.

12. How can I know if the motor is star/delta connection?

The star connection method is that one end of the three-phase windings is connected, and the other end is connected to the three-phase power supply, which is shaped like the letter "Y"; the delta connection method is that the three-phase windings are connected end to end to form a "△" shape, and the top of the triangle is connected to the three-phase power supply.

Their phase voltages are different. Generally, the rated voltage of the star-connected motor is 220V, and the rated voltage of the delta-connected method is 380V. The connection method is generally marked on the inside and outside of the cover plate of the junction box, and different connection methods correspond to different power supply voltages.


13. How does the number of poles of the motor affect its selection?

Motors currently have 2/4/6/8 grade motors, and the number of motor grades for special purposes may be higher. The more pole pairs of the motor, the lower the speed of the motor, but the greater its torque; when choosing a motor, you should consider how much starting torque the load needs, such as starting with a load than no-load The torque required for starting is large. If it is a high-power and large-load starting, the step-down starting (or star-delta starting) should also be considered; as for the matching of the speed of the motor and the load after the number of pole pairs of the motor is determined, it can be considered different. Diameter pulley to drive or match with variable speed gear (gear box). If the power requirement of the load cannot be met after the belt or gear drive is determined after the number of pole pairs of the motor is determined, then the use power of the motor must be considered.

14. What is a series motor and what is the specific principle?

A series-excited (series-excited) motor is a series of stator windings and rotor windings.

Working principle: When the AC power supply is supplied, the principle of generating rotational torque can still be explained by the operation principle of the DC motor. When a current flows through a conductor, a magnetic field is generated around the conductor, and the direction of the magnetic field lines depends on the direction of the current. Put the energized conductor into a magnetic field, and the magnetic field interacts with the magnetic field generated by the energized conductor, which will cause the conductor to be subjected to a force F, and thus cause movement. , when a coil composed of two conductors facing each other is placed in a magnetic field, the two sides of the coil are also subjected to a force, and the two forces are in opposite directions, resulting in a torque. When the coil rotates in the magnetic field, when the corresponding two coil sides turn from one magnetic pole to the other, the direction of the acting force on the conductor will change due to the change of the magnetic field polarity, which also makes the The direction of the torque changes, causing the coil to turn in the opposite direction, so the coil can only swing back and forth around the central axis.

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