You should know these if you are engaged in motor-related work part 2

- May 15, 2018 -

8. What should you watch out for when using a 60Hz motor on a 50Hz power supply?

This is because the current frequency of the motor is lower than the design frequency, the no-load back-EMF generated by the rotation of the motor is reduced, the no-load current is increased, and the motor is damaged. Therefore, the no-load voltage of the motor is required to be reduced.

In frequency conversion speed regulation technology, the frequency of the motor and the stator voltage change at the same time. That is, the frequency decreases, and the voltage also drops at the same time. The motor will not be over-current and will get the ideal operating effect.

9. What is the role of the output reactor in the output terminal of the inverter?

The output reactor is added at the output of the inverter to increase the distance between the inverter and the motor. The output reactor can effectively suppress the instantaneous high voltage generated by the IGBT switching of the inverter and reduce the adverse effect of this voltage on the cable insulation and the motor.

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

10. Can the AC servo motor be controlled by the inverter?

Because the frequency changer and the servo are different in the function and the function, the application is not quite the same, therefore cannot be.

In the case of speed control and torque control, the frequency converter is not required to be very high, and the position feedback is controlled by adding the position feedback signal in the upper position to form a closed-loop frequency conversion. The accuracy and response are not high. Some frequency converters also accept the pulse sequence signal to control the speed, but it seems that the position cannot be controlled directly.

In the occasions with strict position control requirements, it can only be realized by servo. There is also the response speed of the servo is much larger than the frequency conversion, and some occasions with high requirements on the accuracy and response of the speed also use the servo control, and can use the frequency-controlled motion. Most of the occasions can be replaced with servos.

The key is two points: First, the price servo is much higher than the frequency conversion, and the second is the reason of power: the maximum frequency conversion can achieve several hundred KW, and even higher, the maximum servo is tens of KW. The basic concept of servo is accurate, accurate and quick positioning. Frequency conversion is a necessary internal link of servo control, and there are also inverters in the servo drive (stepless speed regulation is required).

11. Can the speed motor start frequently?

Speed-regulating motors can be started frequently. The motors used by our company for debugging are all speed-regulating motors. They often start up so frequently and have never experienced any problems. However, it is of course best to minimize frequent starts. Regardless of how many times the motor is frequently started, it will damage the motor.

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

The star connection method is that one end of the three-phase windings is connected, and the other end is respectively connected to a three-phase power source, 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 “Δ” shape, and the top of the triangle is connected to the three phases again. 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 connection is 380V. The connections are generally indicated inside and outside the cover of the junction box. Different connections correspond to different supply voltages.

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

Motors currently have 2/4/6/8 motors, and special-purpose motor stages may be higher. The more pole pairs of the motor, the lower the speed of the motor, but the greater its torque; when selecting the motor, you need to consider how much starting torque the load requires, such as with a load start than empty The starting torque needs to be large. If it is a high-power and large-load starting, it is also necessary to consider the step-down start (or star delta start); as to determine the matching of the motor's pole pair and the load's rotation speed, you can consider using different Diameter pulleys are used to drive or match with a gear change (gearbox). If the power requirement of the load cannot be reached after the number of motor pole pairs is determined after passing the belt or the gear transmission, the power usage of the motor must be considered.

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

A series-excitation (series-excited) motor is a series connection of a stator winding and a rotor winding.

Working principle: When the AC power supply, the principle of generating the rotating 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 flux depends on the direction of the current. The energized conductor is placed in a magnetic field. This 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 a movement will occur. The conductor will move from the direction of the line of the magnetic flux to the direction of the lean line of magnetic flux. When a coil consisting of two mutually opposite conductors is placed in a magnetic field, the two sides of the coil are also subjected to a force, which is in the opposite direction and generates a moment. When the coil rotates in the magnetic field, the corresponding two coil sides, from one magnetic pole down to the other magnetic pole, when the polarity of the magnetic field has been changed at this time, will change the direction of the force applied to the conductor, and also make The direction of the torque changes so that the coil rotates in the opposite direction, so that the coil can only swing back and forth about the central axis.

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