Tag: VSD debugging

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Some precautions in the selection and use of VFD frequency converters

Operation mode: Some frequency converters cannot be directly controlled by the panel to start/stop. The control terminals must be connected in the forward or reverse direction, that is, the motor direction should be determined by the terminals first, and then the panel can control the start/stop

When the inverter drives the pole changing motor, connect it according to the high-speed connection method, and then run it with speed regulation. If it runs at a lower speed, it can also be connected at a medium speed
For low-power motors with three-phase angle connections of 220V, when switching to a frequency converter, the motor can be connected in a star shape, and can be directly driven by a 380V frequency converter. Its output power remains unchanged, which is much superior to using a method of reducing the output voltage of the frequency converter
When the power supply capacity is several times the capacity of the frequency converter, it will increase the harmonic component of the input current. The loss of rectifier diodes and capacitors will increase and be easily damaged. It is necessary to install input reactors. Installing reactors on the input side can improve power factor, reduce the impact of three-phase current imbalance, and have a certain effect on lightning protection
Installing an output reactor can improve the current waveform, reduce motor operating noise, and improve the energy-saving effect
When there is interference with on-site instruments, lowering the carrier frequency of the frequency converter should be able to improve or eliminate it. The carrier frequency of high-power motors should be moderately lowered. When starting is difficult, in addition to adjusting the starting curve by shortening, the carrier frequency can be reduced
For motors with high operating inertia and requirements for parking time, it is necessary to install braking (braking) units and braking resistors. The parameters should be adjusted to decelerate and stop. When driving the submersible pump motor, a frequency converter with one gear higher power should be selected because its rated current is larger than that of ordinary motors

When using a single frequency converter for constant pressure water supply control, a deceleration shutdown method can be used, similar to soft shutdown, to avoid the occurrence of water hammer effect. However, when using a one to several or power frequency bypass, the shutdown method should be free shutdown. Otherwise, during operation, switching can easily cause the contactor to trip and impact the inverter module of the frequency converter due to the back electromotive force generated by the motor winding
The setting of torque boosting parameters should be tested and carefully considered. When adjusting too high, that is, at low frequencies, the motor end is too high, causing the motor winding to become overexcited and produce magnetic saturation, resulting in a significant reduction in torque. The motor emits a buzzing sound but cannot rotate, and the measured output current increases significantly, which can easily trigger OC faults. In such situations, reducing the parameter for torque boosting can often solve the problem
When parameters need to be changed but cannot be modified, they may have been set for parameter protection or restricted for some reason. Relevant parameters can be set to cancel parameter protection, or parameter initialization can be performed directly. For places with severe dust, it is necessary to supervise the user, regularly clean and blow dust, and take certain dust prevention measures
When wiring low-power frequency converters (below 1kW), attention should be paid. It is best to first check the voltage level label on the nameplate, which indicates that it is 220V or 380V. If it is 220V, the power input often has three terminals: R, S, T, and should be connected with a live wire and a neutral wire. When mistakenly connecting three-phase 380V, powering on will damage the frequency converter. Many users have suffered this loss. We hope that the frequency converter manufacturer can indicate on the terminals
The power supply of the frequency converter is generally introduced using an air circuit breaker. When a contactor is connected, it is only used for protection and trips. The on/off operation of this contactor cannot be used for start/stop operation, and terminals or panels should be used for control. When using the on/off operation of the contactor for start/stop, it causes repeated charging and discharging of the energy storage capacitor inside the frequency converter, which will shorten the life of the capacitor and cause impact on the rectifier module
Signal shielding wire should be grounded at one end. Grounding at both ends can cause circulating currents and introduce interference. In areas prone to lightning strikes, lightning arresters should be installed near the incoming line of the frequency converter and reliably grounded nearby to prevent lightning strikes
The frequency converter is designed according to the rated current of a four pole motor. When applied to motors with more poles, the power capacity of the frequency converter needs to be increased due to the larger rated current of the motor
Due to high-frequency leakage current in the output circuit of the frequency converter, the motor casing or control cabinet casing may have numbness, and both must be reliably grounded. Ordinary circuit breakers with leakage protection cannot be used as power switches. If leakage protection switches must be installed, special ones for the frequency converter must be installed or isolation transformers must be used for power isolation to avoid tripping of the leakage switch. In addition, reducing the carrier frequency can effectively reduce the leakage current value
The power supply of the frequency converter should be introduced using an air circuit breaker instead of a fuse. When one phase fuse blows or has poor contact, it can easily cause phase loss operation, which is detrimental to both the frequency converter and the motor
Measuring the input current of a frequency converter rarely achieves a high degree of balance. Due to differences in the parameters of the rectifier components or differences in the wire diameter, significant differences in input current can occur. Based on experience, an imbalance within 30%, or even slightly larger, can be considered normal

The motor can work with a power frequency power supply, but after using a frequency converter, it frequently trips, such as OC faults. This is because there is a weak link in the insulation of the motor winding, but it has not yet entered the insulation breakdown state under the power frequency sine AC voltage. Although the output current of the frequency converter is similar to a sine wave, its output voltage waveform is a high-frequency pulse train of tens of kHz, which will cause a high induced sharp pulse voltage, making the motor winding prone to turn to turn short circuits or in a semi breakdown state, The amplitude of transient fault current is generated, causing a fault shutdown

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Fluctuations in frequency values and causes of false shutdowns of kemron VFD and their solutions

Install four low-power Comron brand frequency converters in one control cabinet, using proportional synchronous speed control method for synchronous speed control of cutting, water supply, and belt conveyor in gypsum board production line. For the convenience of operation and monitoring, the control panel of the frequency converter is installed on the front of the cabinet and connected with the signal cable provided by the manufacturer.

During on-site debugging, it was found that the displayed speed values of each frequency converter fluctuated by more than plus or minus 30 revolutions during operation! The user suspects that the speed is unstable and requests a solution.
Firstly, the G terminal of the main circuit was independently grounded, and the speed control signal line was shielded and grounded on one side. The fluctuation of the speed value has been improved, but it has not been eradicated yet. Inquire with the manufacturer and answer that it is caused by interference. It is recommended to carry out grounding treatment. After being ineffective, the manufacturer cannot propose a better solution. During the trial run, it was found that there were still fluctuations in the operation of a single unit. There are more running units, resulting in greater fluctuations. Some of the four machines have larger fluctuations, while others have smaller fluctuations, but after all, the speed values cannot be stabilized. This problem was ultimately not completely solved, but it seemed to have little impact on operation, so it was left unresolved.
Later, a similar equipment was installed in another gypsum board factory. After running for several months, the user reported that one of the 3.7kW water supply frequency converters had repeatedly stopped, and the number of shutdowns in a day reached more than ten times. The user requested an on-site solution.
On site observation: The speed display value of the frequency converter fluctuates greatly during operation, with all three digits flashing, and the FWD indicator light also flashing. The speed value suddenly drops to zero during operation, or it may immediately increase and continue to operate, or it may need to be restarted to operate. Sometimes after shutdown, F000 is displayed and enters the parameter setting state for no reason, as if someone has performed shutdown and parameter adjustment operations. However, this “person” is definitely interfering with the signal, causing the CPU of the frequency converter to receive shutdown instructions or other operation instructions. The running current of the 3kW motor is only 2.6A, and there are no fault codes such as overvoltage, undervoltage, or overload when the frequency converter is shut down. Obviously, both the motor and the frequency converter are not fault protected shutdown. Running the frequency converter alone, the phenomenon still persists; Remove all the connections between the start/stop terminals and the speed control terminals, but the phenomenon still persists; Switching to the control panel for start/stop and speed regulation, the phenomenon still persists; Switching to a 5.5kW frequency converter for operation, the phenomenon still persists!
The above phenomenon was determined to be caused by signal interference. Firstly, conventional grounding treatment was also carried out; 2. After being ineffective, the carrier frequency of the frequency converter was adjusted to the lowest carrier frequency of 2kHz, resulting in slight improvement; 3. After wrapping a layer of tin foil on the connecting cable from the control panel to the frequency converter, the number of shutdowns has been reduced, indicating an improvement; 4. After purchasing a magnetic ring with a moderate diameter and winding 2-3 turns at each end of the connecting wire, the displayed speed value and the flashing FWD indicator light disappeared. The speed value was incredibly stable, and even the fluctuation of 1 revolution disappeared!

Interference is the carrier wave at the output end of the frequency converter after it operates, which enters the I/O port of the CPU through the connection cable on the operation panel! For those with less interference, there is fluctuation in input frequency and display value; If the interference is severe, a random shutdown phenomenon will occur. The effect of wrapping a magnetic ring on the signal line to suppress interference is very good.