1. What does the motor protection rating mean?
For example, ip23’s motor refers to a motor that prevents solid objects larger than 12 mm from intruding, and prevents human fingers from touching internal parts to prevent foreign objects of medium size (12 mm in diameter) from intruding. It can prevent the intrusion of sprayed water, or prevent the water sprayed in the direction of the vertical angle less than 60 degrees from entering the damage.
The ip (international protection) protection rating system was drafted by iec (international electrotechnical commission). The motor is classified according to its dust and moisture resistance characteristics. The foreign objects referred to here include tools, human fingers, etc., which are not accessible to live parts of the motor to avoid electric shock. The ip protection class is composed of two numbers. The first figure indicates the level of dust from the motor to prevent intrusion of foreign objects. The second figure indicates the degree of confinement of the motor against humidity and water intrusion. The greater the 娄 character, the degree of protection. The higher.
2. I want to do the experiment of motor frequency conversion speed control. Can the ordinary motor realize frequency conversion speed regulation? Or must I buy a variable frequency motor?
To do the motor speed control experiment with ordinary AC motor on the line.
DC motors can also be frequency-converted. For example, DC inverter air conditioners nowadays convert AC power to DC power and send them to the power module. The module is controlled by the control signal sent from the microcomputer. The difference between the AC and the inverter is that the module output is affected. The controlled DC power is sent to the DC motor of the compressor to control the displacement of the compressor so as to achieve “frequency control.”
3. What kind of motor is AC frequency conversion motor?
In simple terms, inverter technology is used in the control of AC motors. AC frequency conversion motor is actually a kind of motor that adjusts the frequency of AC power to adjust the speed. The frequency of AC power adjustment depends on the inverter. The motor itself will not be frequency-converted. In many occasions where the requirements are not high, it is to take the common motor and inverter to adjust the speed. Variable frequency motor use.
4. How is the snoring after the motor plus frequency converter?
The buzzing sound is caused by the inverter output waveform carrier frequency. Usually if your inverter is a fixed carrier, then the motor screams, and the human ear stimuli is relatively large, then you can By adjusting the carrier frequency (inverter technical manual has this function parameter in the function table). The higher the carrier frequency, the smaller the sound, but the higher the carrier, the more easily the motor will heat up. Therefore, consider the carrier frequency you are using based on the heating program and the emitted sound. Normally, the carrier frequency is the most suitable at the rated current. Normally, you do not need to change him!
If the frequency converter uses a random carrier, then the squeaking sound from the motor will be softer, but the sound will generally be better than the sound of the fixed carrier. Ha ha (easier to accept), if you do not accept, or that you want to mute running, you can also adjust the carrier frequency upwards, adjusted to the satisfaction.
5. Can inverter single-phase 220v make three-phase 380v?
It is not possible. The inverter itself cannot boost the voltage, and it can’t change three-phase 380v from single-phase 220v. This is theoretically feasible, using a transformer to raise the single-phase 220v to 380v, and then converting the single-phase 380v to three-phase 380v.
6. Emerson ev2000 37kw inverter display e018 how to deal with?
You can use a multimeter to measure the contactor coil circuit is normal, check whether the plug on the board is loose or poor contact, the small relay on the driver board is working properly, the contactor auxiliary contact is bad, you can wipe the grinding or replace the contactor. 7. The belt that the high-power motor drags has a speed reducer connected with the electric motor, the function of the speed reducer here?
The purpose of the reducer can be summed up briefly:
1) Reduce the speed and increase the output torque at the same time. The proportion of the torque output will be based on the output of the motor by the deceleration pen, but be careful not to exceed the rated torque of the reducer.
2) Deceleration reduces the load inertia at the same time, and the inertia reduction is the square of the reduction ratio. We can see that the general motor has an inertial data.
8. What is the reason for the slow speed at the start of the motor?
If only the start speed is slow, normal after starting. This may be caused by a mismatch in the starting capacitor, or by the fact that the motor design is originally designed (according to the design of the site), or it may be due to factors such as excessive load resistance and excessive start-up times.
If the speed is slow after start-up, the problem may be that the voltage is insufficient, the capacitance does not match, and the rotational resistance is large.
9. How to choose the brush of rotor winding bushing of induction motor?
It is mainly determined based on whether the working condition of the brush satisfies the current density (a/cm2) and the linear velocity (m/s) of the circumferential edge of the collector ring. Formula: 1 brush load (a) = brush current density (a/cm2) × brush width l (cm) x brush thickness b (cm) ≥ motor rotor rated current (a); 2 collector The circumferential speed of the circle around the circle (m/s) = the rated speed of the motor (r/m)/60(s) × the circumference of the slip ring (m) ≤ the applicable range of the brush (m/s).
Its commonly used brushes are non-ink brush, electrochemical graphite brush and metal graphite brush. During use, attention should be paid to checking brush activity, brush pressure and wear. The brush should be able to move freely up and down in the brush holder without any jamming. When brushing the brush, both sides of the brush can be smoothed on the emery cloth. The pressure of the brush should be properly adjusted according to the type and model of the brush. At present, the brush pressing spring attached to the brush holder is mostly a tension and compression spring, and the pressure thereof gradually decreases as the brush wears, so the brush pressure during the operation of the motor should be adjusted at any time.
10. What does z and th mean in transformer sfz-32000/220th?
According to jb3837, z is the meaning of on-load pressure regulation and th is used in the humid tropical zone.
11. Consult the 60hz motor for use on the 50hz power supply. What do you need to pay attention to?
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.
12. Is the same motor 50hz the same as the 60hz motor resistance?
If the output power is the same, the resistance is the same.
Pe=ea*u*sin@/xe (The letters are not the same)
Nk s \ m g+upe is the electromagnetic power of the generator, ignoring the stator resistance, the electromagnetic power is equal to the generator active power $z:r ~r u
#e7x z `r z:l cea is the generator electromotive force; q d r a g u is the bus voltage of the infinite system
@ is the angle between ea and u, called the power angle. *d \8b x9x#f |,l q6^\+j
Xe is the total reactance 2c le-m*q%z from the generator to the infinity system bus, including the generator reactance.
13. AC servo motor can be controlled by inverter?
Since the frequency converter and servo are different in performance and function, the application is not the same, so it is not possible:
1. In the occasions of speed control and torque control, the general inverter is not very high, and the feedback signal of the upper position plus the position feedback signal is used to control the position using the frequency conversion of the closed loop. 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. The
The
2, in the strict position control requirements of the occasion can only use the servo to achieve, there is the servo response speed is much greater than the frequency conversion, some of the speed of the accuracy and response to the occasion also requires high servo control, can use the frequency control Almost all of the sports venues 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 the power: the maximum frequency conversion can achieve several hundred kw, or even higher, and 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).
14. Can the speed motor be started 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.
15. How can you ask a master to know that the motor is △/y connected?
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.
16. How does the number of poles of the motor influence its selection?
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.
17. Ask what is a string motor, 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 in the direction of the lean line of magnetic flux from the magnetic field line. 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.
18. For a submersible pump with a rated current of 12a, the maximum starting current is 227a. At this time, the upstream switch thermomagnetic protection trip will be triggered.
The instantaneous value of the starting current is irrelevant to the load. Even if the pump blade is stuck, the maximum value of the instantaneous value of the starting current should not change. If the pump is jammed, the starting current will only last longer and will not drop (this may cause tripping of the thermomagnetic protection of the upstream switch).
If the insulation of the motor windings to ground is normal, the reason for the large maximum starting current is likely to be caused by the reason that the insulation resistance value of the windings or between the windings is reduced. It is easier to check the phase-to-phase insulation drop, and it is very difficult to check the drop in insulation between turns.
The reason that the maximum value of the starting current is too large may also be that some phase of the three-phase winding is disconnected (if the winding is double-wired and wound). The DC resistance of the three-phase windings can be measured with two-arm bridges. If a large deviation is found, one of the phases should be suspected of disconnection (phase disconnection with large resistance).
In addition, it should also pay attention to whether or not the motor is connected in parallel with a capacitor that improves the power factor. If the performance of the capacitor is deteriorated, the starting current value will be too large.
19. How to judge the quality of three-phase asynchronous motor?
Summarize how to determine the quality of the three-phase asynchronous motor coil, what instrument to check:
1. Megohmmeter; Can be used to measure the insulation resistance between the motor phases and relative ground, and can not be less than 0.5 megohm.
2. Multimeter; used to check the motor coil on and off measurements.
3. Single-arm bridge; Accurate measurement of coil resistance, you can know whether the resistance of each phase coil is close, especially after re-wrapping.
The failure of the motor is nothing more than two blocks: mechanical and electrical.
Mechanical aspects include:
1, the bearing is lack of oil or damage,
2. Does the end cap “run the jacket” and does the bearing “run inside”?
The main electrical aspects are:
1. Is the insulation resistance qualified?
2. Is the three-phase DC resistance qualified? Bridge measurement with both arms.
3, the rotor is broken? The DC resistance of the motor is an important basis for judging the motor.
20. Is it possible to add circuit breakers and fuses to the neutral line?
1. When there is only a single-phase circuit, a circuit breaker can be added, that is, the zero line can enter the switch and enter the fuse;
2, three-phase circuit, the zero line should not enter the circuit breaker, into the switch, into the fuse.
twenty one. Does the motor soft starter save energy?
The soft-start energy-saving effect is limited, but it can reduce the impact of start-up on the power grid, it can also achieve smooth start-up and protect the motor unit.
According to the energy conservation theory, due to the addition of a relatively complex control circuit, soft start will not only not save energy, but also increase the energy consumption, but it can reduce the starting current of the circuit and play a role in protection.
twenty two. When using the inverter to run, what is the starting current and starting torque of the motor?
With the inverter running, the starting current is limited to 150% or less of the rated current (125% to 200% depending on the model) as the motor speeds up the frequency and voltage accordingly. When starting with the power frequency power supply directly, the starting current is 6~7 times. Therefore, mechanical and electrical impact will occur. The inverter drive can be started smoothly (the starting time becomes 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 the inverter with the torque automatic enhancement function, the starting torque is more than 100%, and it can be started with full load.
twenty three. Is there any connection between overload and short circuit of the motor?
There are two kinds of overload of the motor; 1. It is the overload of the mechanical load, it is the overload that drives the load beyond the rated value or the drive system has jamming phenomenon, this has nothing to do with the short circuit, 2. The load is normal, the motor current is overloaded, This may be a short circuit between the motor windings with local ground and between turns.
twenty four. What is the application of variable frequency speed regulation and what are the benefits?
What is the application of variable frequency speed regulation?
Can it be applied to rotating machinery with speed control requirements? What are the benefits?
Before the implementation of variable frequency speed control (theory has long been realized, but the real realization is after the invention of power electronic devices) The disadvantages of traditional speed regulation using DC and DC speed regulation are:
1, DC motor structure is complex, high maintenance costs
2, due to the presence of the commutator, DC motor power has no more
Therefore, the benefits of variable frequency speed regulation are:
1, can make the AC motor to get the same excellent speed control performance than DC speed
2. AC squirrel-cage asynchronous motor is easy to maintain
3, AC motor power does not exist commutator restrictions
25. Is 100kva transformer used to supply 300kw electrical appliances (37kw max) enough?
How much load can a 100kva transformer carry? Look at the following formula to know
p=capacity*power factor*80%=100*0.9*80%=72kw
Normally overloading 20% for 1 hour is allowed, so it is sufficient.
Mainly to see the total current is not super super, 100kva transformer high-voltage current is 5.8a, low-voltage current is 150a, even if the occasional super does not matter, mainly to see the temperature rise not more than 55 degrees. The temperature rise is equal to the actual temperature minus the ambient temperature.
26. How to measure the insulation resistance of the motor?
If it is a three-phase AC motor, measure the phase-to-phase and earth-to-ground insulation resistance of the three-phase winding of the motor.
If it is a DC motor, measuring the armature winding of the motor to the ground, the series winding to the ground, he excited the winding to the ground, and the series winding excited the winding to him.
Select the corresponding shaking table according to the motor voltage level to be measured.
Measurement steps:
—Disconnect the power
—Discharge to ground
—If it is a three-phase AC motor to open the center point (if possible)
—If it is a DC motor, lift the brush.
— Use the oscilloscope to detect the insulation resistance between the phases and the ground
—Discharge to ground
—Restoration line
— Record insulation resistance, and ambient temperature on the case
27. What is a brushless acyclic starter?
The brushless and acyclic starter is a kind of starting equipment that overcomes the shortcomings of winding asynchronous motor equipped with slip ring, carbon brush and complicated starter, and retains the advantages of small starting current of the winding motor, large starting torque and so on. . All original three-phase wound rotor AC induction motors (variable with speed, with the exception of those fitted into the camera) that were originally started with resistance starters, reactors, frequency-sensitive rheostats, liquid rheostat starters, and soft starters (jr, jzr, yr, yzr) Can use “brushless acyclic starter” to update.
28. There are several ways to start the motor capacitor?
There are two types of startup:
1. Capacitor start (refers to capacitor disconnection after motor starts);
2. Capacitor starts and runs (refers to the capacitor that is responsible for starting and participating in the operation).
29. A plastic extrusion device is controlled by Yaskawa’s inverter. It has been more than one year. At present, for every hour of operation, the inverter shows motor overload. Is the fault a motor problem or a frequency conversion problem?
This question, in the absence of certainty, is both possible:
1. The motor may also be overloaded due to a long time of use, large running current after grinding loss, or raw materials extruded by the manufacturer without being hardened or unqualified.
2. Since the inverter has been used for more than one year, the current detection circuit on the power board is faulty, or the sensor is damaged. It is also useful to adjust the acceleration time. It is also a way to improve the working environment, such as cleaning up dust and working temperature.
30. Can the transformer be used as a load for the frequency converter?
In principle, it should be possible, but it is not practical in practice. The frequency converter is not boosted by transformers, and it should be of a type that can be used for circuits above 380v. If higher voltages are required, then there are also direct 220V or 380v direct conversion and then double voltage mode to obtain high voltage circuit can be used. Inverter is mainly used for load drive (such as motor), rarely used for power conversion, and the function of the inverter is not only limited to the frequency conversion itself, there are many additional features, such as various types of protection, if you use the inverter To obtain a variable frequency power supply is not desirable from an economical point of view, it is recommended to use other frequency conversion circuits.
31. Can the frequency converter be adjusted to 1hz, the maximum number of hz can be used?
If the inverter is used in a general AC asynchronous motor, the inverter is close to DC when it is adjusted to 1hz, which is absolutely not possible. The motor will operate at the maximum current within the limit of the inverter, and the motor will generate heat severely. Burned the motor.
If more than 50hz operation will increase the iron loss of the motor, it is also unfavorable to the motor. Generally, it is better not to exceed 60hz (more than a short time is allowed), otherwise it will also affect the service life of the motor.
32. What is the principle of the frequency regulation resistor of the frequency converter? Why adjust the resistance can change the frequency?
The frequency adjustment resistor of the frequency converter is used to divide the 10V reference voltage of the frequency converter in proportion and send it back to the main control board of the frequency converter. The main control board of the frequency changer returns the voltage of the resistance and then reads the data by analog-digital conversion, and then converts the proportional value of the rated frequency to output the current frequency. Therefore, adjusting the resistance value can adjust the frequency of the frequency converter.
33. How to calculate the generator power calculation formula?
Generator rated power = voltage x current ie (p=uxi)
The motor nameplate is generally marked as 24v or 12v. Therefore, when some customers calculate the voltage, the company used is 24(12) x current, and the calculated power is very different from what our company says. In fact, 24V or 12V is the nominal voltage of the national vehicle system, but the generator’s operating voltage is higher than the battery voltage in order to charge the battery, so the actual operating voltage is 28v or 14v, respectively. Therefore, the motor power should be its operating voltage x current, ie 28 (14) x current.
For example: jfb271-c its nameplate nominal 24v 70a, its power should be 28vx70a = 1960w, generally also known as 2000w motor.
34. Can the converter decouple the motor current?
Can frequency converter be decoupled? Can not! But as long as the output frequency f and synchronous speed n1 make the slip rate in the stable zone or the rated slip se, it is equal to the decoupling of the motor current, because the rotor power factor is 1 at this moment, and the rotor current is decoupled. The torque current to control! The frequency converter is the speed regulation device of the asynchronous motor, it can’t exceed the mechanical characteristic of the asynchronous motor to carry out so-called any control!
35. Why does the current flow when the induction motor starts up? After starting, the current will become smaller?
When the induction motor is in the stop state, from the electromagnetic point of view, just like the transformer, the stator winding connected to the power source is equivalent to the primary coil of the transformer, and the closed circuit rotor winding is equivalent to the secondary coil shorted by the transformer; the stator winding There is no electrical connection between the rotor windings and only magnetic connections. The magnetic flux passes through the stator, air gap, and rotor core into a closed circuit. When the closing moment, the rotor has not yet turned up due to inertia, the rotating magnetic field cuts the rotor winding at the maximum cutting speed—synchronous rotation speed, so that the rotor winding induces the highest potential that can be reached, and therefore, flows through the rotor conductor very large Current, this current produces magnetic energy that counteracts the magnetic field of the stator, just as transformer secondary flux counteracts the effect of one magnetic flux.
In order to maintain the original magnetic flux that adapts to the power voltage at that time, the stator automatically increases the current. Because the current of the rotor is very large, the stator current also increases greatly, even as high as 4 to 7 times of the rated current, which is why the starting current is large.
Why is the current small after start-up: As the motor speed increases, the stator magnetic field cuts the speed of the rotor conductor decreases, the induced potential in the rotor conductor decreases, and the current in the rotor conductor also decreases, so that the stator current is used to counteract the rotor current. The part of the current that is affected by the magnetic flux also decreases, so the stator current goes from large to small until it is normal.
36. Consult the influence of carrier frequency on inverter and motor?
Carrier frequency affects inverter output current
(1) The higher the operating frequency, the greater the duty cycle of the voltage wave, and the smaller the current harmonic component, ie, the higher the carrier frequency, the better the smoothness of the current waveform;
(2) The higher the carrier frequency, the smaller the current the inverter allows to output.
(3) The higher the carrier frequency, the smaller the capacitive reactance of the wiring capacitor (because xc=1/2πfc), the larger the leakage current caused by the high frequency pulse.
Effect of carrier frequency on the motor
The higher the carrier frequency, the smaller the vibration of the motor, the lower the operating noise, and the less the motor heating. However, the higher the carrier frequency, the higher the frequency of the harmonic current, the more serious the skin effect of the motor stator, and the greater the motor loss, the smaller the output power.
37. Why can’t inverter be used as variable frequency power supply?
The entire circuit of the variable frequency power supply is composed of AC current, AC current, and filtering. Therefore, the output voltage and current waveforms are pure sine waves, which are very close to the ideal AC power supply. It can output the grid voltage and frequency of any country in the world.
The frequency converter is composed of alternating current, an alternating current (modulation wave) and other circuits, and the standard name of the frequency converter should be a frequency converter. The output voltage waveform is a pulse square wave, and there are many harmonic components. The voltage and frequency change at the same time and can’t be adjusted separately. It does not meet the requirements of the AC power supply. In principle, the use of power supply can not be used, generally only for the three-phase asynchronous motor speed control.
38. When using the inverter, why is the motor temperature rise higher than the power frequency?
Because the output voltage waveform of the inverter is not a sine wave but a deformed wave, the motor current at the rated torque is about 10% higher than the power frequency, so the temperature rise is slightly higher than the power frequency.
There is another point: When the motor speed decreases, the motor cooling fan speed is not enough, the motor temperature rise will be higher.
39. Why is an earth leakage circuit breaker easy to trip when using a frequency converter?
This is because the inverter’s output waveform contains higher harmonics, and the motor and the cable between the inverter and the motor generate a leakage current. This leakage current is much larger than the power frequency drive motor, so this phenomenon occurs.
Leakage current at the output side of the inverter is about 3 times more than that at the power frequency operation. Leakage current such as a motor is added. The operating current of the leakage protector should be greater than 10 times the leakage current at the power frequency.
40. Ask the inverter output terminal to add output reactor, what is its role?
The output reactor is added at the output of the inverter to increase the conductor distance from the inverter to the motor. The output reactor can effectively suppress the instantaneous high voltage generated by the igbt switch of the inverter and reduce the adverse effects 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 voltage rise rate of the motor winding to 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 (eg igbt) in the inverter.
41. Does inverter air conditioner save energy and energy?
1, can reduce the starting current, reduce the impact on the grid, extend the life of the compressor, to achieve energy saving. Imagine the following one district only uses a power transformer, air conditioning in summer once the transformer overload switch, again Is it closed? If you use inverter air conditioners, it’s much better.
2, when the indoor temperature decreases automatically reduce the frequency that is to reduce the compressor speed, while the air conditioning inside the electronic expansion valve automatically shut down to keep the temperature of the outdoor unit radiator, so that the radiator heat transfer temperature difference is not constant, that is, to maintain air conditioning The energy efficiency ratio remains the same. It always works under higher efficiency, and eventually reaches the thermal equilibrium. That is, the heat transferred into the room from the outside is equal to the heat from the air conditioner to the outside. As the ordinary air conditioner decreases with the decrease of the indoor air temperature, the operating temperature of the outdoor unit radiator also decreases. At this time, the difference in the heat transfer temperature reduces the cooling effect. At this time, the energy ratio of the air conditioner decreases, and the air conditioner cannot always maintain a high efficiency. under.
42. What should pay attention to when one inverter drags multiple motors?
1. It can be more than one, but it must be used in the translation mechanism.
2. The control mode must be v/f. Vector control cannot be used.
3. The inverter capacity should be >= motor capacity, depending on the load characteristics.
4. Each motor should be heated and protected.
43. Does DC speed regulation really be eliminated? Is there no use value?
In the speed control, position control are basically eliminated.
However, in terms of torque control, despite the vector control, direct torque control and other methods, the inverter can not replace the superior performance of DC speed control.
44. Ask the inverter grounding problem?
1, all instruments alone to do the grounding line.
2. The interference of the inverter is in the form of odd-order harmonics in the power grid, and the impact is greater 5, 7, and 11 times. It is difficult to completely eliminate the interference with the inverter, and it can be self-tested or find a local power experiment. Whether the interference was judged to have exceeded the standard.
45. What is the direct torque control of the inverter?
The simplest benefits are high starting torque and low output torque, fast response speed, high torque accuracy, and strict requirements on motor parameters. However, compared with the vector control, the torque ripple at the low speed and high speed is large.
46. Can the motor be reversed?
Motor can be reversed! Only under special circumstances, the reverse rotation of the motor is not allowed, not that the motor cannot be reversed!
Whether we ask for a positive or negative reversal depends mainly on the status of my job requirements. It does not mean that the motor itself cannot be reversed.
47. Will the concept of high voltage inverter?
A: According to international practice and China’s national standards, the division of voltage levels is called high voltage when the power supply voltage is ≥10kV, and medium voltage when it is 1kv～10kv. We also customarily refer to motors with a rated voltage of 6 kV or 3 kV as “high-voltage motors.” Since the frequency converters with corresponding rated voltages of 1 to 10 kV have common characteristics, we refer to inverters that drive 1 to 10 kV AC motors as high-voltage inverters. High-voltage inverter is divided into two types of nature, current type and voltage type, and its characteristics are different:
(1) The main function of the inverter is the inverter circuit. According to the DC-end filter type, the inverter circuit can be divided into voltage type and current type. The former has a large capacitor in parallel with the DC power supply input. On the one hand, it can suppress the pulsation of the DC voltage and reduce the internal resistance of the DC power supply, making the DC power supply approximately a constant voltage source; on the other hand, it is the reactive current from the inverter side. Provide a conduction path. Therefore, it is called a voltage type inverter circuit.
(2) A large inductor is connected in series with the DC power supply side of the inverter, so that the DC power supply is approximately a constant current source. Such a circuit is called a current-type inverter circuit. The inductance in series in the circuit can suppress the pulsation of direct current on the one hand, but the output characteristic is soft. Current-mode inverters are an early topology developed before voltage-type inverters.
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48. What are the advantages of the delta connection of the motor compared to the star connection? Why do we have to work with a delta connection after conversion?
1, the same one motor, can be installed into a winding y-type winding, winding can also be installed into △-type winding;
2. When the same motor is installed and wound into a delta-type winding, the cross section of the conductor is small, the number of series turns is large, the working phase voltage is high, and the phase current is low;
3, the same one motor, winding into a y-type winding, the conductor section is large, the number of series turns is small, the working phase voltage is low, the phase current is high;
4, △-type windings require better three-phase symmetry, power supply symmetry must be higher, so that there will be no circulation, otherwise it will heat, increase the loss;
5, y-type windings in the three-phase symmetry is not good, the power supply symmetry is not high, there will be no circulation, but there will be zero drift, three-phase work is seriously asymmetric;
6, in use, △-type winding can start with y-△ start-up mode, and y-type winding can not start with y-△ start mode;
7, because the resistance heat loss is proportional to the square of the current, so the same a motor, the installation of winding into the △-type winding heat loss.
49. The motor is burned, why does the thermal protection not jump?
There may be the following reasons:
1. If the thermal protection setting value is too large, the setting value should be selected to be slightly larger than the normal operating current (except for frequent starting of the motor), and the best effect is obtained.
2. Thermal relay quality problems, poor quality, deterioration of performance after long-term work, the best choice for new or imported products, such as Siemens 3ua series.
3. When the internal coil of the motor is short-circuited, the thermal relay will not act, and the air switch shall act. Two approaches
1. Use time relay, delay on time relay.
2. Using the inverter to start slowly
I used the second method, a device originally equipped with 5.5kw high-speed motor. Because the start-up time is too long, the motor is often damaged during the start-up process, the starting current is about 70a, time is about 25s. Every one or two months will damage a Motor.
After the change to 7.5kw motor failure remains. At the time just have a 15kw inverter is not used, it is installed on the use. Start time is set to 60 seconds, the device has not yet damaged a motor.
50. Inverter leakage circuit breaker error malfunction technology
In everyday use, we have installed a leakage protector in the input circuit of the inverter, but the leakage circuit breaker often trips after power transmission, and the reason cannot be found. Many people think that there is a problem with the quality of the inverter. In fact, there is a reason for this and an analysis of this issue.
Leakage Circuit Breaker Rated Current Design
Inverter output is controlled by pwm (Pulse Width Modulation, similar to high-speed switch), so high-frequency leakage current will occur. To install a general leakage breaker on the primary side of the inverter, it is recommended to select each inverter as an option. The leakage current of 200mA or more and the operating time of 0.1 second or more is used for shutoff. However, it cannot be guaranteed that the leakage will not be broken. The following factors must be considered to determine the magnitude of the system leakage current and select appropriate The leakage circuit breakers and necessary measures to improve the tripping of leakage breakers after power transmission.
The formula for selecting the rated current of the general leakage breaker is as follows:
iΔn ≧ 10*[ig1+ign+3*(ig2+igm)]
Ig1, ig2: Leakage current of cable during commercial operation.
Ign: The leakage current of the noise filter at the input side of the inverter.
Igm: Leakage current of the motor during commercial operation.
According to the relevant parameters of the above formula, the factors affecting the leakage current are:
(1) Leakage current of cable (There are two parts)
• Leakage current switch Leakage current of the cable length of the filter.
• Leakage current of the cable length of the inverter motor.
(2) Leakage current of filter (including inverter).
(3) The leakage current of the motor.
The leakage current value of each part (unit: ma)
(1) The leakage current of the cable = a* (actual cable length/1000m); the cable manufacturer provides a leakage current value a for each wire diameter of 1000m.
(2) Leakage current of the filter (including the inverter) – supplied by the inverter supplier. For example: Delta’s vfd055b43b filter is 26tdt1w4b4 with a maximum leakage current of 70ma.
(3) The leakage current of the motor – provided by the motor supplier.
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