1. What does the protection level of an electric motor mean?
For example, an IP23 rating for a motor means that it can prevent the intrusion of solid objects larger than 12mm, prevent human fingers from touching internal parts, and prevent the intrusion of medium-sized foreign objects (diameter greater than 12mm). It can also prevent the intrusion of sprayed water, or prevent water sprayed at an angle of less than 60 degrees from entering and causing damage.
The IP (International Protection) rating system was drafted by the IEC (International Electrotechnical Commission). It classifies motors according to their dust and moisture protection characteristics. Foreign objects, including tools and human fingers, must not come into contact with the live parts inside the motor to avoid electric shock. The IP protection rating consists of two digits: the first digit indicates the level of dust and foreign object protection, and the second digit indicates the degree of moisture and water resistance. A higher IP number indicates a higher level of protection.
2. I want to conduct a motor frequency conversion speed control experiment. Can a regular motor achieve frequency conversion speed control? Or do I have to buy a frequency conversion motor?
For the experiment of variable frequency speed control of motors, a regular AC motor will suffice.
DC motors can also achieve frequency conversion, such as in modern DC inverter air conditioners: they convert industrial frequency AC power into DC power and send it to the power module. The module is controlled by control signals sent by a microcomputer. Unlike AC inverters, the module outputs controlled DC power to the DC motor of the compressor to control the compressor's displacement, thereby achieving "frequency conversion speed regulation".
3. What kind of motor is an AC variable frequency motor?
Simply put, it means that frequency conversion technology is used in the control of AC motors. An AC variable frequency motor is actually a type of motor that adjusts its speed by regulating the frequency of the AC power supply. Adjusting the AC frequency requires a frequency converter; the motor itself does not change frequency. In many applications where the requirements are not high, a regular motor is used as an AC variable frequency motor by adding a frequency converter for speed regulation.
4. What causes a buzzing sound when a frequency converter is added to a motor?
The "humming" sound you're hearing is caused by the carrier frequency of the inverter's output waveform. If your inverter uses a fixed carrier frequency, the motor will typically emit a high-pitched screeching sound, which can be quite irritating to the ear. You can adjust the carrier frequency (this parameter is listed in the inverter's technical manual). A higher carrier frequency results in a quieter sound, but it also makes the motor more prone to overheating. Therefore, you need to consider both the overheating rate and the sound when choosing your carrier frequency. Generally, the optimal carrier frequency is set at the factory for the rated current, and you usually don't need to change it.
If the inverter uses a random carrier wave, the "humming" sound from the motor will be softer, but it will generally be more pleasant to listen to than the sound of a fixed carrier wave. (Hehe, it's easier for people to accept). If you don't like it, or if you want to operate silently, you can increase the carrier frequency until you are satisfied.
5. Can a single-phase 220V frequency converter output three-phase 380V?
No, it's not possible. A frequency converter itself cannot boost voltage, let alone convert single-phase 220V to three-phase 380V. Theoretically, it's possible to use a transformer to boost single-phase 220V to 380V, and then convert that single-phase 380V to three-phase 380V.
6. How to handle the E018 error displayed on an Emerson EV2000 37kW frequency inverter?
You can use a multimeter to check if the contactor coil circuit is normal, check if the plugs on the board are loose or have poor contact, check if the small relays on the drive board are working properly, and check if the contactor auxiliary contacts are faulty. You can clean, polish, or replace the contactor. 7. High-power motors driven by belts usually have a speed reducer connected to the motor. What is the function of the speed reducer here?
The uses of speed reducers can be briefly summarized as follows:
1) While reducing speed, increase output torque. The torque output ratio is calculated by multiplying the motor output by the reduction gear, but care must be taken not to exceed the rated torque of the reduction gearbox.
2) Deceleration reduces the load's inertia, and the reduction in inertia is the square of the reduction ratio. You can see that most motors have an inertia value.
8. Please explain why the motor starts at a slow speed.
If the starting speed is slow but normal after starting, it could be due to a mismatched starting capacitor, the motor's inherent design (depending on the environment), or excessive load resistance causing the long starting time.
If the engine speed is still slow after starting, the problem may be insufficient voltage, capacitor mismatch, or high rotational resistance.
9. How to select the brushes for the rotor slip rings of a wound-rotor asynchronous motor?
The current carrying capacity (A) is mainly determined based on whether the brush's operating conditions meet the requirements of current density (A/cm²) and linear velocity (m/s) at the circumference of the slip ring. The formulas are: ① Brush current carrying capacity (A) = Brush current density (A/cm²) × Brush width L (cm) × Brush thickness b (cm) ≥ Rated rotor current of the motor (A); ② Linear velocity (m/s) at the circumference of the slip ring = Rated motor speed (r/m) / 60 (s) × Slip ring circumference (m) ≤ Applicable range of the brush (m/s).
There are three common types of brushes: non-graphite brushes, electrographite brushes, and metal-graphite brushes. During use, it is important to regularly check the brush movement, brush pressure, and degree of wear. The brush should move freely up and down in the brush holder without any obstruction. To prevent the brush from getting stuck, simply smooth the two sides of the brush on sandpaper. The brush pressure should be adjusted appropriately according to the type and model of the brush. Currently, the brush clamping springs attached to the brush holder are mostly tension/compression springs, and their pressure gradually decreases as the brush wears. Therefore, the brush pressure should be adjusted continuously during motor operation.
10. In transformer SFZ-32000/220TH, what do Z and TH mean?
According to JB3837, Z means on-load tap changer, and TH indicates use in humid tropical regions.
11. What precautions should be taken when using a 60Hz motor on a 50Hz power supply?
This is because the motor's current frequency is lower than the design frequency. In order to reduce the no-load back electromotive force generated during its rotation and increase the no-load current, which would damage the motor, the no-load voltage needs to be reduced.
In variable frequency speed control technology, the motor's frequency and stator voltage change simultaneously. That is, as the frequency decreases, the voltage must also decrease simultaneously to prevent overcurrent in the motor and achieve the desired operating effect.
12. Why is an output reactor added to the output terminal of a frequency converter? What is its function?
Adding an output reactor to the output terminal of the frequency converter increases the distance between the frequency converter and the motor. The output reactor can effectively suppress the instantaneous high voltage generated when the frequency converter's IGBT switches, reducing the adverse effects of this voltage on cable insulation and the motor.
The main function of a reactor is to limit the capacitive charging current of the motor connection cable and to limit the voltage rise rate on the motor winding to within 540V/μs. It is also used to passivate the steepness of the inverter output voltage (switching frequency) and reduce the disturbance and impact on power components (such as IGBTs) in the inverter.
13. Can an AC servo motor be controlled by a frequency converter?
Because frequency converters and servo drives differ in performance and function, and their applications are also quite different, it is not possible to use them together.
1. In applications where speed and torque control requirements are not very high, frequency converters are generally used. Some frequency converters also use a closed-loop control system with position feedback signals added to the host computer for position control, but the accuracy and response are not high. Some frequency converters now also accept pulse sequence signals to control speed, but they don't seem to be able to directly control position.
2. In situations requiring strict position control, only servo motors can achieve this. Also, the response speed of servo motors is much faster than that of frequency converters. Servo motors are also used in some situations where high speed accuracy and response are required. In almost all motion situations where frequency converters can be used for control, servo motors can replace frequency converters.
The key differences are twofold: first, servo motors are significantly more expensive than frequency converters; second, power consumption differs: frequency converters can reach hundreds of kilowatts or even higher, while servo motors only reach tens of kilowatts at most. The fundamental concept of a servo motor is accurate, precise, and rapid positioning. Frequency conversion is an essential internal component of servo control, and servo drives also incorporate frequency conversion (for stepless speed regulation).
14. Can a variable speed motor be started frequently?
Speed-regulating motors can start frequently; our company uses them for testing and commissioning, and they frequently start without any problems. However, minimizing frequent starts is always best. Regardless, excessive starting will damage the motor.
15. How can I tell if a motor is connected in a delta (Δ) or y-axis configuration?
In a star connection, one end of the three-phase windings is connected, and the other end is connected to the three-phase power supply, forming a shape like the letter "Y". In a delta connection, 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 a star-connected motor is 220V, while the rated voltage of a delta-connected motor is 380V. The connection method is usually marked on the inside or outside of the junction box cover, and different connection methods correspond to different power supply voltages.
16. How does the number of poles of a motor affect its selection?
The more pole pairs a motor has, the lower its speed, but the greater its torque. When selecting a motor, you need to consider the starting torque required by the load. For example, a motor starting under load requires more torque than one starting under no-load. For high-power, high-load starting, you also need to consider reduced-voltage starting (or star-delta starting). Regarding matching the motor's pole pair count with the load speed, you can consider using pulleys of different diameters or a gearbox. If, after determining the motor's pole pair count, the power required by the belt or gear transmission cannot meet the load's power requirements, then you need to consider the motor's operating power.
17. Could you please explain what a series-wound motor is and what its specific operating principle is?
A series-wound motor is a motor in which the stator winding and the rotor winding are connected in series.
Working Principle: The principle of generating rotational torque when powered by AC power can still be explained using the operating principle of a DC motor. When 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. When a current-carrying conductor is placed in a magnetic field, the interaction between this magnetic field and the magnetic field generated by the current-carrying conductor will cause the conductor to experience a force F, thus producing motion. The conductor will move from the direction of denser magnetic field lines to the direction of sparser magnetic field lines. When a coil consisting of two opposing conductors is placed in a magnetic field, the two sides of the coil also experience forces, and these two forces are in opposite directions, generating torque. When the coil rotates in the magnetic field, the corresponding two coil sides move from one magnetic pole to the other. At this time, because the polarity of the magnetic field changes, the direction of the force on the conductor changes, and the direction of the torque also changes, causing the coil to rotate in the opposite direction. Therefore, the coil can only oscillate back and forth around its central axis.
18. A submersible pump with a rated current of 12A has a maximum starting current of 227A, which will trigger the thermal-magnetic protection of the upstream switch to trip.
The instantaneous value of the starting current is independent of the load, and even if the pump impeller is jammed, it should not cause a change in the maximum value of the instantaneous starting current. If the pump impeller is indeed jammed, it will only cause the starting current to last for a longer period of time and not decrease (which may cause the upstream switch thermal magnetic protection to trip).
If the insulation of the motor windings to ground is normal, the reason for an excessively high maximum starting current is likely due to a decrease in the insulation resistance between phases or between turns of the windings. Checking for a decrease in phase-to-phase insulation is relatively easy, but checking for a decrease in inter-turn insulation is much more difficult.
Another reason for an excessively high starting current is a partial break in one phase of the three-phase winding (if the winding uses a double-wire parallel winding). A double-arm bridge can be used to measure the DC resistance of the three-phase winding. If a large deviation is found, a partial break in one phase (the phase with the higher resistance) should be suspected.
In addition, it should be noted whether the motor has a capacitor connected in parallel to improve the power factor. If the capacitor performance deteriorates, it will also cause the starting current value to be too high.
19. How to determine if a three-phase asynchronous motor is good or bad?
To summarize, here's how to determine the condition of a three-phase asynchronous motor coil and what instruments to use for testing:
1. Megohmmeter; can be used to measure the insulation resistance between phases and between phase and ground in motors, and the resistance must not be less than 0.5 megohms.
2. Multimeter; used to check the continuity of motor coils.
3. Single-arm bridge; accurately measures coil resistance, allowing you to determine if the resistance of each phase coil is close, especially after rewinding.
Electric motor failures can be broadly categorized into two types: mechanical and electrical.
In terms of machinery:
1. Check if the bearing is lacking oil or damaged.
2. Is the end cap "moving out of its outer sleeve"? Is the bearing "moving out of its inner sleeve"?
The main electrical aspects include:
1. Is the insulation resistance up to standard?
2. Is the three-phase DC resistance up to standard? Measure it using a double-arm bridge.
3. Is the rotor bar broken? The DC resistance of the motor is an important basis for judging the motor.
20. Can a circuit breaker and a fuse be added to the neutral wire?
1. When there is only a single-phase circuit, a circuit breaker can be added, that is, the neutral wire and the live wire can go to the switch or the fuse;
2. In a three-phase circuit, the neutral wire must never go into a circuit breaker, switch, or fuse.
21. Can a motor soft starter save energy?
Soft start has limited energy-saving effect, but it can reduce the impact of starting on the power grid and achieve smooth starting, thus protecting the motor unit.
According to the law of conservation of energy, due to the addition of relatively complex control circuits, soft start not only does not save energy, but also increases energy consumption. However, it can reduce the starting current of the circuit and play a protective role.
22. When operating with a frequency converter, what are the starting current and starting torque of the motor?
When using a frequency converter, the frequency and voltage increase accordingly as the motor accelerates, limiting the starting current to below 150% of the rated current (125%~200% depending on the model). Direct starting with a mains frequency power supply results in a starting current 6~7 times the rated current, causing mechanical and electrical shocks. Frequency converters allow for smooth starting (though starting time is longer). The starting current is 1.2~1.5 times the rated current, and the starting torque is 70%~120% of the rated torque; for frequency converters with automatic torque boosting, the starting torque is over 100%, allowing for full-load starting.
23. What is the relationship between motor overload and short circuit?
There are two types of motor overload: 1. Mechanical overload, which is when the driven load exceeds the rated value or there is a jamming phenomenon in the transmission system. This has nothing to do with short circuit. 2. Normal load, but motor current overload, which may be due to a local short circuit to ground or between turns in the motor winding.
24. In what applications is variable frequency speed control used? What are its advantages?
In what applications is variable frequency speed control used?
It can be applied to rotating machinery that requires speed regulation.
What are the benefits?
Before the realization of variable frequency speed control (which was theoretically possible long ago, but actually realized after the invention of power electronic devices), traditional speed control used DC. The disadvantages of DC speed control are:
1. DC motors have complex structures and high maintenance costs.
2. Due to the presence of the commutator, there is not much room for improvement in the power of DC motors.
Therefore, the advantages of variable frequency speed control are:
1. It can enable AC motors to achieve speed regulation performance that is as excellent as DC speed regulation.
2. AC squirrel-cage asynchronous motors are simple and convenient to maintain.
3. AC motor power is not limited by the commutator.
25. Is a 100KVA transformer sufficient to supply a total power of 300kW of electrical appliances (maximum 37kW)?
What load can a 100KVA transformer handle? The calculation formula below will tell you.
P = Capacity * Power Factor * 80% = 100 * 0.9 * 80% = 72KW
Running at 20% overload for 1 hour is generally permissible, so it's sufficient.
The main thing to check is whether the total current exceeds the limit. For a 100KVA transformer, the high-voltage current is 5.8A and the low-voltage current is 150A. Even if it occasionally exceeds the limit, it's not a big deal. The main thing to watch out for is that the temperature rise doesn't exceed 55 degrees Celsius. The temperature rise equals the actual temperature minus the ambient temperature.
26. How do I measure the insulation resistance of a motor?
If it is a three-phase AC motor, measure the insulation resistance between phases and to ground of the three-phase windings of the motor.
For DC motors, measure the armature winding to ground, series winding to ground, separately excited winding to ground, and series winding to separately excited winding. Inverter soft starter sales center: 15037162627
Select the appropriate megohmmeter based on the voltage level of the motor being tested.
Measurement steps:
---Disconnect the power
---Discharge to ground
---If it's a three-phase AC motor, open the center point (if possible).
---If it is a DC motor, lift the brushes.
---Use a megohmmeter to test the phase-to-phase and phase-to-ground insulation resistance respectively.
---Discharge to ground
---Restored Line
---Record the insulation resistance and ambient temperature.
27. What is a brushless, ringless starter?
Brushless and ringless starters are starting devices that overcome the disadvantages of wound-rotor asynchronous motors, which have slip rings, carbon brushes, and complex starting devices, while retaining the advantages of wound-rotor motors, such as low starting current and high starting torque. All JR, JZR, YR, and YZR three-phase wound-rotor AC asynchronous motors (excluding variable-speed and those equipped with phase shifters) that were originally started using resistance starters, reactors, frequency-sensitive rheostats, liquid rheostats, or soft starters can be replaced with brushless and ringless starters.
28. What are the different types of capacitor starting methods for motors?
There are two ways to start:
1. Capacitor starting (refers to the capacitor being disconnected after the motor starts);
2. Capacitor starts and operates (meaning the capacitor is responsible for both starting and operating).
29. A plastic extrusion machine, whose motor is controlled by a Yaskawa frequency converter, has been in operation for over a year. Currently, every hour of operation, the frequency converter displays a motor overload warning. Is this a problem with the motor or the frequency converter?
In the absence of a definitive answer, both possibilities exist:
1. Overload may also occur due to the motor running at high current after prolonged use and wear, or due to the manufacturer's poorly refined or substandard plastic extrusion raw materials.
2. Since the inverter has been used for over a year, the current detection circuit on the power board may be faulty, or the sensor may be damaged. Adjusting the acceleration time might help. Improving the working environment is also an option, such as cleaning dust and controlling the operating temperature.
30. Can a transformer be used as a load for a frequency converter?
In principle, it should be possible, but in practice, it's impractical. Even without a transformer for voltage boosting, there should be inverter models suitable for circuits above 380V. For even higher voltages, there are circuits that directly convert 220V or 380V and then use a voltage multiplier to obtain the high voltage. Inverters are primarily used for load driving (such as motors), rarely for power supply frequency conversion. Furthermore, the function of an inverter extends far beyond frequency conversion itself, including many additional functions such as various protections. Using an inverter to obtain a variable frequency power supply is economically inadvisable; alternative frequency conversion circuits are recommended.
31. Can the frequency converter be adjusted to 1Hz? What is the highest Hz it can be used in?
If a frequency converter is used on a general AC asynchronous motor, the frequency converter is already close to DC when it is set to 1Hz, which is absolutely not allowed. The motor will operate at the maximum current limit of the frequency converter, which will cause the motor to overheat and may burn out the motor.
Running at frequencies above 50Hz will increase the iron losses in the motor, which is detrimental to the motor. It is generally best not to exceed 60Hz (exceeding it for a short period of time is permissible), otherwise it will also affect the service life of the motor.
32. What is the working principle of the frequency adjustment resistor in a frequency converter? Why can adjusting the resistor change the frequency?
The frequency adjustment resistor in a frequency converter is used to proportionally divide the 10V reference voltage of the frequency converter and then send the voltage back to the main control board of the frequency converter. The main control board then performs analog-to-digital conversion on the voltage returned by the resistor, reads the data, and then converts it into a proportional value of the rated frequency to output the current frequency. Therefore, adjusting the resistor value can adjust the frequency of the frequency converter.
33. How is the formula for calculating generator power calculated?
Generator rated power = voltage x current, i.e. (P = U x I)
Motor nameplates are generally marked as 24V or 12V. Therefore, some customers use 24(12)X current when calculating the voltage, resulting in a significant difference between the calculated power and what our company states. In reality, 24V or 12V are the nominal voltages for vehicle systems as stipulated by national regulations. However, the generator's operating voltage must be higher than the battery voltage to charge the battery, so the actual operating voltages are 28V or 14V respectively. Therefore, the motor power should be its operating voltage X current, i.e., 28(14)X current.
For example, the nameplate of JFB271-C is marked as 24V70A, and its power should be 28V x 70A = 1960W, which is also commonly referred to as a 2000W motor.
34. Can a frequency converter decouple the motor current?
Can a frequency converter decouple the motor? No! However, as long as the output frequency f and synchronous speed n1 keep the slip rate in the stable region or at the rated slip rate Se, it is equivalent to decoupling the motor current. This is because the rotor power factor is 1 at this time, and the rotor current is the torque current that needs to be decoupled and controlled! A frequency converter is a speed control device for asynchronous motors; it cannot exceed the mechanical characteristics of the asynchronous motor to perform any so-called control!
35. Why does an induction motor draw a large current when starting, and then the current decreases after starting?
When an induction motor is stationary, from an electromagnetic perspective, it resembles a transformer. The stator winding connected to the power source is equivalent to the primary coil of the transformer, while the closed-circuit rotor winding is equivalent to the short-circuited secondary coil. There is no electrical connection between the stator and rotor windings, only a magnetic connection; the magnetic flux forms a closed circuit through the stator, air gap, and rotor core. At the instant the circuit is closed, before the rotor starts rotating due to inertia, the rotating magnetic field cuts the rotor windings at its maximum cutting speed—synchronous speed—causing the rotor windings to induce the highest possible electromotive force. Consequently, a large current flows through the rotor conductors. This current generates magnetic energy that cancels out the stator magnetic field, just as the secondary magnetic flux in a transformer cancels out the primary magnetic flux.
In order to maintain the original magnetic flux that is compatible with the power supply voltage at that time, the stator automatically increases the current. Because the rotor current is very large at this time, the stator current also increases significantly, even reaching 4 to 7 times the rated current. This is the reason for the large starting current.
Why is the current small after startup? As the motor speed increases, the speed at which the stator magnetic field cuts the rotor conductor decreases, the induced electromotive force in the rotor conductor decreases, and the current in the rotor conductor also decreases. As a result, the part of the stator current used to counteract the magnetic flux generated by the rotor current also decreases, so the stator current decreases from large to small until it returns to normal.
36. What is the effect of carrier frequency on frequency converters and motors?
The carrier frequency affects the output current of the frequency converter.
(1) The higher the operating frequency, the larger the duty cycle of the voltage wave and the smaller the higher harmonic components of the current. That is, the higher the carrier frequency, the better the smoothness of the current waveform.
(2) The higher the carrier frequency, the smaller the current that the inverter can output;
(3) The higher the carrier frequency, the smaller the capacitive reactance of the wiring capacitor (because Xc=1/2πfC), and the greater the leakage current caused by the high-frequency pulse.
The effect of carrier frequency on motors
The higher the carrier frequency, the less vibration, the lower the operating noise, and the less heat the motor generates. However, the higher the carrier frequency, the higher the frequency of harmonic currents, the more severe the skin effect of the motor stator, the greater the motor losses, and the lower the output power.
37. Why can't a frequency converter be used as a variable frequency power supply?
The entire circuit of a frequency converter power supply consists of AC-DC, AC, and filtering components, resulting in pure sine waves for both its output voltage and current, closely resembling an ideal AC power supply. It can output the grid voltage and frequency of any country in the world.
A frequency converter is composed of circuits such as AC-DC-AC (modulated wave). The standard name for a frequency converter should be variable frequency speed controller. Its output voltage waveform is a pulsed square wave with many harmonic components. The voltage and frequency change proportionally simultaneously and cannot be adjusted separately, which does not meet the requirements of AC power supply. In principle, it cannot be used as a power supply and is generally only used for speed control of three-phase asynchronous motors.
38. Why is the motor temperature rise higher when using a frequency converter than when using the mains frequency?
Because the output voltage waveform of the frequency converter is not a sine wave but a distorted wave, the motor current at rated torque is about 10% higher than that at the power frequency, so the temperature rise is slightly higher than that at the power frequency.
Another point is that when the motor speed decreases, the motor cooling fan speed is insufficient, and the motor temperature rises higher.
39. Why do residual current circuit breakers (RCCBs) tend to trip when used with frequency converters?
This is because the output waveform of the frequency converter contains high-order harmonics, and leakage current will be generated in the motor and the cable between the frequency converter and the motor. This leakage current is much larger than that when the motor is driven by the mains frequency, so this phenomenon occurs.
The leakage current on the output side of the inverter is about three times that of the mains frequency operation. In addition, the leakage current of the motor, etc., should be selected. The operating current of the leakage current protection device should be more than 10 times that of the leakage current at the mains frequency.
