Fault causes and preventive measures of the hottes

2022-08-19
  • Detail

Fault causes and preventive measures of frequency converter

frequency converter is composed of main circuit, power circuit, IPM drive and protection circuit, cooling fan, etc. Its structure is mostly in the form of unit or modularization. Because the use method is incorrect or the setting environment is unreasonable, it will be easy to change 3 Special (aliphatic/alicyclic) isocyanates: mainly including 6 methylene 2 isocyanate (HDI), isophorone 2 isocyanate (IPDI), 2 cyclohexylmethane (4), 4'-2 isocyanate (hmdi) and other aliphatic/alicyclic isocyanate frequency devices misoperate and fail, or fail to 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

1.1 common fault analysis of the main circuit

the main circuit is mainly composed of three-phase or single-phase rectifier bridge, smoothing capacitor, filter capacitor, IPM inverter bridge, current limiting resistor, contactor and other components. Many common faults are caused by electrolytic capacitors. The service life of electrolytic capacitor is mainly determined by the DC voltage applied at both ends and the internal temperature. The model of capacitor has been selected in the circuit design, so the internal temperature plays a decisive role in the service life of electrolytic capacitor. Electrolytic capacitors will directly affect the service life of the frequency converter. Generally, the service life will be halved when the temperature rises by 10 ℃. Therefore, on the one hand, proper ambient temperature should be considered during installation, and on the other hand, measures can be taken to reduce pulsating current. Using AC or DC reactors with improved power factor can reduce the pulsating current and prolong the service life of electrolytic capacitors

when maintaining capacitors, the deterioration of electrolytic capacitors is usually judged by the electrostatic capacity that is relatively easy to measure. When the electrostatic capacity is lower than 80% of the rated value and the insulation resistance is below 5 m Ω around the new material industry, electrolytic capacitors should be considered to be replaced

1.2 typical fault analysis of main circuit

fault phenomenon: overcurrent tripping occurs when the frequency converter accelerates, decelerates or operates normally

first of all, it is necessary to distinguish whether it is caused by load or frequency converter. If it is the fault of the frequency converter, the current at the time of tripping can be queried through the historical records, which exceeds the rated current of the frequency converter or the set value of the electronic thermal relay, and the three-phase voltage and current are balanced, whether there is overload or sudden change, such as motor locked rotor, should be considered. When the load inertia is large, the acceleration time can be appropriately extended, and this process will not damage the frequency converter itself. If the current at the time of tripping is within the rated current of the frequency converter or the setting range of the electronic thermal relay, it can be judged that the IPM module or related parts have failed. First, you can judge whether the IPM module is damaged by measuring the forward and reverse resistance between the output terminals u, V, w of the main circuit of the frequency converter and the terminals P and N on the DC side respectively. If the module is not damaged, the drive circuit is faulty. If IPM module overcurrent or inverter short circuit to ground trips during deceleration, it is generally the module of the upper half of the inverter or its driving circuit fault; The over-current of IPM module during acceleration is caused by the failure of the module of the lower half bridge or its driving circuit. The causes of these failures are mostly caused by the external dust entering the inverter or the humidity of the environment

1.3 control circuit fault analysis

the control circuit affects the service life of the frequency converter is the power supply part, which is the smoothing capacitor and the buffer capacitor in the IPM circuit board. Its principle is the same as the above, but the pulsating current passing through the capacitor here is a fixed value that is basically not affected by the load of the main circuit, so its service life is mainly determined by the temperature and power on time. Since the capacitors are welded on the circuit board, it is difficult to judge the deterioration by measuring the electrostatic capacity. Generally, it is estimated whether it is close to its service life according to the ambient temperature and service time of the capacitor

the power circuit board provides power to the control circuit, IPM drive circuit, surface operation display board, fan, etc. these power supplies are generally obtained from the DC voltage output from the main circuit through switching power supply and then rectification respectively. Therefore, in addition to the damage of the rectifier circuit of this circuit, the short circuit of a certain power supply may also affect the power supply of other parts, such as the short circuit between the control power supply and the public ground due to misoperation, resulting in the damage of the switching power supply part on the power circuit board, and the short circuit of the fan power supply leading to the power failure of other power supplies, etc. Generally, it is easy to find out by observing the power circuit board

the logic control circuit board is the core of the frequency converter, which integrates CPU, MPU, ram, EEPROM and other large-scale integrated circuits. It has high reliability, and the probability of failure itself is very small, but sometimes all control terminals will be closed at the same time due to startup, resulting in EEPROM failure of the frequency converter. As long as the EEPROM is reset

ipm circuit board includes drive and buffer circuits, as well as overvoltage and loss protection circuits. The PWM signal from the logic control board inputs the voltage drive signal into the IPM module through optical coupling. Therefore, while detecting the mode speed, the optocoupler on the IPM module should also be measured

1.4 cooling system

the cooling system mainly includes fins and cooling fans. Among them, the service life of the cooling fan is relatively short. Near the service life, the fan vibrates, the noise increases, and finally stops running, and the frequency converter trips due to IPM overheating. The service life of the cooling fan is limited by the bearing, which is about 10000 ~ 35000 H. When the frequency converter operates continuously, the fan or bearing needs to be replaced every 2 ~ 3 years. In order to prolong the service life of fans, fans of some products only operate when the frequency converter is running rather than when the power is on

1.5 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. The specific methods to reduce noise interference are as follows: the control coils of all relays and contactors around the frequency converter shall be equipped with absorption devices to prevent impulse voltage, such as RC surge absorber, whose wiring shall not exceed 20 cm; Try to shorten the wiring distance of the control circuit and separate it from the main circuit; The distance between the twisted joint of the inverter control circuit wiring should be more than 15 mm, and the distance between the twisted joint and the main circuit should be more than 10 cm; When the frequency converter is far away from the motor (more than 100 m), on the one hand, the cross-sectional area of the conductor can be increased to ensure that the line voltage drop is within 2%. At the same time, the output reactor of the frequency converter should be installed to compensate the charging current of the distributed capacitance generated by the long-distance conductor. The grounding terminal of the frequency converter shall be grounded according to the regulations, which must be reliably grounded at the special grounding point, and cannot be mixed with electric welding and power grounding; A radio noise filter is installed at the input end of the frequency converter to reduce the input high-order harmonics, so as to reduce the noise impact from the power line to electronic equipment; At the same time, a radio noise filter is also installed at the output end of the frequency converter to reduce the line noise at its output end

1.6 installation environment

the frequency converter is an electronic device, which has strict requirements for the installation environment, and there are detailed requirements for the installation and use environment in its instructions. 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, and rubber and other vibration avoidance measures should be taken for occasions with large vibration and impact; Humidity, corrosive gas and dust will cause corrosion, 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 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 air heater should be taken

1.7 abnormal power supply

abnormal power supply 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. Sometimes, the clamps required are 5 flowers and 8 doors 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 directly started motors, induction cookers and other equipment nearby, in order to prevent the voltage reduction caused by these equipment when they are put into operation, their power supply should be separated from the power supply of the frequency converter to reduce mutual influence

for the equipment that can continue to operate after instantaneous power failure, in addition to selecting the frequency converter with appropriate price, the speed reduction ratio of motor load should also be considered in advance. When both the frequency converter and the external control circuit adopt the instantaneous power failure compensation method, after the voltage loss is restored, the speed measurement motor is used to prevent the overcurrent during acceleration

for equipment requiring continuous operation, the frequency converter shall be equipped with an automatic switching uninterruptible power supply device. For example, the frequency converter with diode input and single-phase control power supply can continue to work although it is in the state of lack of phase, but 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 frequency converter, it should be checked and handled as soon as possible

1.8 lightning strike, induced lightning

the impulse voltage formed by lightning strike or induced lightning strike may 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 short-circuit opening will produce a high impulse voltage. 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. RC surge absorber shall be added to vacuum circuit breaker. If there is a vacuum circuit breaker on the primary side of the transformer, the frequency converter should be disconnected before the vacuum circuit breaker acts in the control sequence

2 fault self diagnosis and prevention function of frequency converter

the old transistor frequency converter mainly has the following disadvantages: easy to trip, not easy to restart, and low overload capacity. Due to the rapid development of IGBT and CPU, perfect self diagnosis and fault prevention functions have been added to the inverter, which greatly improves the reliability of the inverter

if the "all field automatic torque compensation function" in the vector control inverter is used, the fault 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

Here I want to say 1

in addition, because the software development of the frequency converter is more perfect, 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 shutdown; Automatically reset internal faults and maintain continuous operation; When the load torque is too large, it can automatically adjust the operation curve and

Copyright © 2011 JIN SHI