Problems encountered in the use of the hottest fre

  • Detail

Problems encountered in the use of the frequency converter and fault prevention

due to the incorrect use method or unreasonable setting environment, it is easy to cause the frequency converter malfunction and failure, or can not meet the expected operation effect. In order to nip in the bud, it is particularly important to carefully analyze the cause of the failure in advance. External electromagnetic induction interference

if there are interference sources around the frequency converter, they will invade the interior of the frequency converter through radiation or power lines, causing the control circuit to malfunction, causing abnormal operation or shutdown, and even damaging the frequency converter in serious cases. It is important to improve the anti-interference ability of the frequency converter itself, but due to the limitation of device cost, it is more reasonable and necessary to take external noise suppression measures to eliminate interference sources. The following measures are specific methods to implement the three no principles for noise interference: the control coils of all relays and contactors around the frequency converter need to be equipped with absorption devices to prevent impulse voltage, such as RC absorbers; Try to shorten the wiring distance of the control circuit and separate it from the main line; The use of shielded wire circuit shall be specified according to the regulations. If the line is relatively small, a reasonable relay method shall be adopted; The grounding terminal of the frequency converter shall be carried out according to the regulations, and cannot be mixed with electric welding and power grounding; A noise filter is installed at the input end of the frequency converter to avoid interference from the incoming line of the power supply

installation environment

the frequency converter is an electronic device, and there are detailed requirements for installation and use environment in its specification. In special cases, if these requirements cannot be met, corresponding suppression measures must be taken as far as possible: vibration is the main cause of mechanical damage to electronic devices at the same time, and rubber and other vibration avoidance measures should be taken for occasions with large vibration and impact; Humidity, corrosive gas and dust will cause rust, poor contact and low insulation of electronic devices to form a short circuit. As a preventive measure, the control board should be treated with anti-corrosion and dust prevention, and adopt a closed structure; Temperature is an important factor affecting the life and reliability of electronic devices, especially semiconductor devices. Air conditioners should be installed according to the environmental conditions required by the device or direct sunlight should be avoided

in addition to the above three points, it is also very necessary to regularly check the air filter and cooling fan of the frequency converter. For special cold occasions, in order to prevent the microprocessor from working normally due to low temperature, necessary measures such as setting space heaters should be taken

abnormal power supply

abnormal power supply shows various forms, but it can be roughly divided into the following three types, namely, phase failure, low voltage, power failure, and sometimes their mixed forms. The main reasons for these abnormal phenomena are mostly caused by wind, snow and lightning strike on the transmission line, and sometimes because of short circuit to ground and phase to phase in the same power supply system. Lightning strike varies greatly due to region and season. In addition to voltage fluctuations, some electric or self generating units will also have frequency fluctuations, and these phenomena sometimes occur repeatedly in a short time. In order to ensure the normal operation of the equipment, corresponding requirements are also put forward for the power supply of the frequency converter

if there are direct starting motors, induction cookers and other equipment nearby, in order to prevent the voltage reduction caused by these equipment when they are put into operation, they should be separated from the inverter power supply system to reduce mutual influence; For occasions requiring continuous operation after instantaneous power failure, in addition to selecting the frequency converter with appropriate price, the speed reduction ratio of the load motor is also considered in advance. The frequency converter and external control circuit adopt the instantaneous stop compensation method. When the voltage is restored, the overcurrent during acceleration is prevented by speed tracking and the detection of speed measuring motor; For the equipment that must be operated, the frequency converter shall be equipped with an automatic switching uninterruptible power supply device

although the inverter with diode input and single-phase control power supply can continue to work in the state of lack of phase, the current of some devices in the rectifier is too large and the pulse current of the capacitor is too large. If it operates for a long time, it will have a negative impact on the service life and reliability of the inverter, so it should be checked and handled as soon as possible

lightning strike, induced lightning

the impulse voltage formed by lightning strike or induced lightning strike can sometimes cause damage to the frequency converter. In addition, when the primary side of the power system is equipped with a vacuum circuit breaker, the opening and closing of the circuit breaker can also produce a higher impulse voltage. When the vacuum circuit breaker at the primary side of the transformer is disconnected, a high voltage surge peak is formed at the secondary side through coupling

in order to prevent overvoltage damage caused by impulse voltage, it is usually necessary to add absorption devices such as varistors at the input end of the frequency converter to ensure that the input voltage is not higher than the maximum voltage allowed during the main circuit of the frequency converter. When using vacuum circuit breakers, try to use impact to form additional RC surge absorbers. If the painted parts on the surface of the transformer are flat and smooth, there is a vacuum circuit breaker on the primary side of the voltage regulator, because the control sequence ensures that the frequency converter is disconnected before the vacuum circuit breaker acts

the past transistor frequency converter mainly has the following disadvantages: easy to trip, difficult to restart, and low overload capacity. Due to the rapid development of IGBT and CPU, the transition device is also a device with polyester strips. The inverter has added perfect self diagnosis and fault prevention functions. In an interview with plastic news, Zhen Ronghui, the managing director of yizhimi, said that the reliability of the inverter has been improved

if the full field automatic torque compensation function in the vector control inverter is used, the failure causes such as insufficient starting torque and output reduction caused by changes in environmental conditions will be well overcome. This function uses the high-speed operation of the microcomputer inside the frequency converter to calculate the torque required at the current time, and quickly correct and compensate the output voltage to offset the change of the frequency converter output torque caused by the change of external conditions

in addition, due to the more perfect software development of the frequency converter, various fault prevention measures can be set inside the frequency converter in advance, and the continuous operation can be maintained after the fault is resolved, such as restarting the motor in the process of free parking; Automatically reset internal faults and maintain continuous operation; When the load torque is too large, it can automatically adjust the operation curve to avoid trip; It can detect the abnormal torque of the mechanical system

influence of frequency converter on peripheral equipment and fault prevention

the installation and use of frequency converter will also affect other equipment, sometimes even lead to other equipment faults. Therefore, it is very necessary to analyze these influencing factors and study what measures should be taken

high-order harmonic of power supply

because almost all current converters adopt PWM control mode, such pulse modulation form makes the high-order harmonic current generated on the power side when the converter is running, and causes voltage waveform distortion, which has a serious impact on the power system. The following treatment measures are usually taken: use a special transformer to supply power to the converter, which is separated from other power supply systems; Filter reactors or various rectifier bridge circuits are installed on the input side of the frequency converter to reduce the high-order harmonic component. For the occasions with leading phase capacitors, the capacitor current will increase due to the high-order harmonic current, causing serious heating. The reactors must be connected in series in front of the capacitors to reduce the harmonic component, and the electrical induction of the reactors should be analyzed and calculated reasonably to avoid LC oscillation

the temperature of the motor is too high and the operating range

when the frequency conversion speed regulation transformation is carried out for the existing motor, the cooling capacity of the self cooling motor decreases during low-speed operation, causing the motor to overheat. In addition, because the high-order harmonic contained in the output waveform of the frequency converter is bound to increase the iron loss and copper loss of the motor, after confirming the load state and operating range of the motor, the following corresponding measures should be taken: strong cold ventilation for the motor or improve the motor specification level; Replace the special motor for frequency conversion; Limit the operating range and avoid the low-speed zone

vibration and noise

vibration is usually caused by the pulsating torque of the motor and the resonance of the mechanical system, especially when the pulsating torque is exactly consistent with the mechanical resonance. Noise is usually divided into frequency converter noise and motor noise, and different treatment measures should be taken for different installation sites: during the commissioning of the frequency converter, on the premise of ensuring the control accuracy, the pulse torque component should be minimized; Debug and confirm the mechanical resonance points, and use the frequency shielding function of the frequency converter to exclude these resonance points from the operating range; Since the noise of the frequency converter is mainly generated by the electromechanical reactance of the cooling fan, low-noise devices are selected; The AC reactor is reasonably set between the motor and the frequency converter to reduce the high-order harmonic caused by PWM modulation

the peak voltage formed by the high-frequency switch is unfavorable to the motor insulation.

the output voltage of the frequency converter contains high-frequency peak wave voltage. These high-order harmonic impulse voltages will reduce the insulation strength of the motor winding, especially the PWM controlled frequency converter. The following measures should be taken: try to shorten the wiring distance from the frequency converter to the motor; The surge voltage absorption device of blocking diode is used to deal with the output voltage of the frequency converter; For PWM frequency converter, a filter should be added to the input side of the motor as far as possible

Copyright © 2011 JIN SHI