Ten common fault phenomena and fault analysis of t

2022-10-23
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Ten common fault phenomena and fault analysis of frequency converter

1.1 phenomenon

(1) when restarting, it trips as soon as the speed is increased. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts are stuck; Inverter module is damaged; The torque of the motor is too small

(2) it jumps when powered on. This phenomenon generally cannot be reset. The main reasons are: the module is bad, the driving circuit is bad, and the current detection circuit is bad

(3) when restarting, it does not trip immediately, but when accelerating, the main reasons are: the acceleration time setting is too short, the upper current limit setting is too small, and the torque compensation (v/f) setting is high

1.2 example

(1) one lg-is The 7KW frequency converter jumps "OC"

analysis and maintenance as soon as it is started: no sign of burnout is found when opening the cover, and there is basically no problem in measuring the IGBT (7mbr25nf-120). In order to further judge the problem, it is good to measure the opening and closing of the high-power transistors of 7 units after removing the IGBT. When measuring the drive circuit of the upper half axle, it was found that one circuit was significantly different from the other two circuits. After careful inspection, it was found that the output pin of an optocoupler a3120 was short circuited with the negative pole of the power supply, and the three circuits after replacement were basically the same. The module is installed, powered on and running well

(2) when a beltro-vert2.2kw frequency converter is powered on, it jumps "OC" and cannot be reset

analysis and maintenance: first, check the inverter module and find no problems. Secondly, check that there is no abnormal phenomenon in the driving circuit. It is estimated that the problem is not in this part. It may be due to the overcurrent signal processing. Remove the circuit sensor and power on. It shows that everything is normal. Therefore, it is considered that the sensor is broken. Find a new one and replace it. The test with load is normal

II. Overvoltage (OU)

overvoltage alarm usually occurs during shutdown, and its main reason is that the deceleration time is too short or there is a problem with the braking resistance and braking unit

(1) example

a Taian N2 series 3.7KW frequency converter jumps "Ou" during shutdown

analysis and maintenance: before repairing this machine, we must first find out the reason for the "Ou" alarm. This is because when the frequency converter decelerates, the speed of cutting the rotating magnetic field of the motor rotor winding accelerates, and the electromotive force and current of the rotor increase, so that the motor is in the state of power generation. The feedback energy flows to the DC link through the diode in parallel with the high-power switch in the inverter link, causing the DC bus voltage to rise, Therefore, we should focus on checking the brake circuit. There is no problem in measuring the discharge resistance. When measuring the impact of the screw emitted from the brake pipe (ET191) on the 100mm long fiber composite, it is found that it has broken down. After replacement, it is powered on for operation, and there is no problem in rapid shutdown

III. undervoltage (Uu)

undervoltage is also a problem we often encounter in use. The main reason is that the voltage of the main circuit is too low (220V series is lower than 200V, 380V series is lower than 400V). The main reason is that one circuit of the rectifier bridge is damaged or there is abnormal operation in the three circuits of the thyristor, which may lead to the occurrence of undervoltage fault. Secondly, the contactor of the main circuit is damaged, resulting in the loss of DC bus voltage above the charging resistance, which may lead to undervoltage There is also the undervoltage problem caused by the failure of the voltage detection circuit

3.1 example

(1) a ct18.5kw frequency converter trips "UU" when powered on

analysis and maintenance: after inspection, the charging resistance of the rectifier bridge of this frequency converter is good, but the contactor action is not heard after power on, which makes it difficult for general enterprises to enter, because the charging circuit of this frequency converter does not use the impact tester to detect the knowledge thyristor, but relies on the contact to complete the charging process, so it is considered that the fault may lie in the contactor or control circuit and the power supply, Remove the contactor and separately add 24V DC contactor to work normally. Then check the 24V DC power supply. After careful inspection, the voltage is output after being stabilized by the lm7824 regulator tube. It is measured that the regulator tube has been damaged. Find a new one and replace it. It works normally when powered on

(2) a danfossvlt5004 frequency converter, the power on display is normal, but after loading, it jumps "dclinkundervolt" (DC circuit voltage is low)

analysis and maintenance: this frequency converter is special in terms of phenomenon, but if you carefully analyze the problem, it is not so complicated. The frequency converter also completes the charging process through the charging circuit and contactor. No abnormal phenomenon is found when it is powered on. It is estimated that it is caused by the voltage drop of the DC circuit when loading, and the voltage of the DC circuit is rectified by the full wave rectifier of the rectifier bridge, Then it is provided by the capacitor after smoothing, so we should focus on checking the rectifier bridge. After measurement, it is found that one of the bridge arms of the rectifier bridge is open circuit, and the problem is solved after replacing it with a new one

IV. overheating (OH)

overheating is also a common fault. The main reasons are: the ambient temperature is too high, the fan is locked, the performance of the temperature sensor is poor, and the motor is overheated

example

the customer of an abbacs50022kw frequency converter reported that it jumped "Oh" after running for about half an hour

analysis and maintenance: because the fault occurs after running for a period of time, it is unlikely that the temperature sensor will be damaged. Maybe the temperature of the frequency converter is really too high. After being powered on, it is found that the fan rotates slowly and the protective cover is full of cotton wool (because the frequency converter is used in the relationship between spinning shear stress and shear strain/shear Hooke's law/linear relationship; textile industry). After cleaning, the fan runs well, The fault did not jump again after running for several hours

v. output imbalance

output imbalance is generally manifested in motor jitter and unstable speed. The main reasons are: module failure, drive circuit failure, reactor failure, etc

5.1 example

a Fuji g9s11kw frequency converter, the output voltage difference is about 100V

analysis and maintenance: turn on the machine and preliminarily check the inverter module (6mbi50n-120). No problem is found, and no fault is found in the 6-way drive circuit. After removing the module and measuring, it is found that the high-power transistor of one way bridge cannot be turned on and off normally. The module has been damaged. After confirming that the drive circuit is free of fault, everything is normal after replacing it with a new one

VI. overload

overload is also one of the faults that the frequency converter jumps more frequently. When we see the overload phenomenon at ordinary times, we should first analyze whether it is the motor overload or the overload of the frequency converter itself. Generally speaking, the motor has strong overload capacity. As long as the motor parameters of the frequency converter parameter table are set properly, the motor overload is generally not likely to occur The frequency converter itself is prone to overload alarm due to its poor overload capacity We can detect the output voltage of the frequency converter

VII. Switching power supply damage

this is the most common fault of many frequency converters, which is usually caused by the short circuit of the load of switching power supply. Danfoss frequency converter adopts a new pulse width integrated controller uc2844 to adjust the output of switching power supply. At the same time, uc2844 also has functions such as current detection and voltage feedback. When there is no display, the control terminal has no voltage, DC12V, When the 24V Fan does not work, we should first consider whether the switching power supply is damaged

VIII. SC fault

sc fault is a common fault of Yaskawa inverter. IGBT module is damaged, which is one of the reasons for SC fault alarm. In addition, the damage of the drive circuit is also easy to cause SC fault alarm. In the design of the driving circuit, the upper bridge uses the driving optocoupler PC923, which is an optocoupler with amplification circuit specially used to drive the IGBT module, and the lower bridge driving circuit of Yaskawa uses the optocoupler pc929, which is an optocoupler with amplification circuit and detection circuit inside. In addition, motor jitter, three-phase current, voltage imbalance, frequency display but no voltage output, these phenomena may be IGBT module damage. There are many reasons for IGBT module damage. First, external load failure leads to IGBT module damage, such as load short circuit, locked rotor, etc. Secondly, the aging of the drive circuit may also lead to the distortion of the drive waveform, or the IGBT damage caused by the too large fluctuation of the drive voltage, resulting in the SC fault alarm

IX. GF - grounding fault

grounding fault is also a fault that will be encountered at ordinary times. In addition to eliminating the causes of motor grounding problems, the most likely part of the fault is the hall sensor. Due to the influence of temperature, humidity and other environmental factors, the working point of the hall sensor is easy to drift, resulting in GF alarm

X. current limiting operation

in normal operation, we may encounter the current limit prompted by the frequency converter. For general frequency converters that cannot work normally and smoothly when the current limit alarm occurs, the voltage (frequency) must first drop until the current drops to the allowable range. Once the current is lower than the allowable value, the voltage (frequency) will rise again, resulting in the instability of the system. Danfoss inverter adopts internal slope control to find the working point without exceeding the predetermined current limit, control the motor to run smoothly at the working point, and feed back the warning signal to the customer. According to the warning information, we will check whether there is a problem with the load and motor

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