The trip state is always maintained for the maintenance check before the cause of the fault is removed, the reset is input with the TESET key or the control circuit terminal RST.
The abnormal faults of the frequency converter are divided into two categories: soft fault and hard fault. The former is caused by improper operation or parameter setting. The hard fault is caused by the damage of the inverter itself. It may be inconvenient to repair.
Before handling the fault, pay attention to the operating record of the inverter before the fault, including current, speed, winding and bearing temperature, etc., in order to facilitate the analysis and inspection of the fault.
When the inverter displays a certain type of fault, but the corresponding fault does not occur during the troubleshooting process, you should carefully check the fault detection component or the fault information processing system for any problems.
During fault inspection or maintenance, be careful to cut off the power supply, shake the high voltage cabinet breaker on the input side of the input transformer of the inverter, and disconnect the main switch of the inverter A1 and A2 into the line cabinet, and wait for 8 minutes. After the capacitor is discharged, the cabinet door can be opened for maintenance. Do not check immediately after shutdown.
Due to the rated operation of the inverter, the DC bus voltage can reach 1000V, and the number of electrolytic capacitors used for filtering reaches 120. The single capacity is 6800μF, which stores a large amount of power. After the shutdown, the voltage balance resistor in front of the capacitor module will be After the discharge, after the voltage is lowered (the discharge time is 8 min), the cabinet can be opened for inspection.
In general, the common protection functions of the inverter have the following aspects.
2 over current protection
The overcurrent protection object in the inverter mainly refers to the sudden change of the current exceeding the overcurrent detection value (about 200% of the rated current). The inverter shows that OC indicates overcurrent, because the overload capability of the inverter device is higher. Poor, so the inverter's overcurrent protection is a crucial part.
2.1 Analysis of the cause of overcurrent
Overcurrent faults can be divided into acceleration, deceleration, and constant speed overcurrent.
It may be caused by the acceleration/deceleration time of the inverter being too short, the load is abrupt, the load is not evenly distributed, and the output is short-circuited.
At this time, it is generally solved by extending the acceleration/deceleration time, reducing the sudden change of the load, adding the energy-consuming braking element, performing the load distribution design, and checking the line.
If the load inverter is disconnected or the overcurrent fault occurs, the inverter inverter circuit is broken and the inverter needs to be replaced.
According to the inverter display, you can find the reasons from the following aspects:
(1) Overcurrent during operation, that is, the drag system has an overcurrent during the working process.
The reasons are roughly as follows:
â— First, the motor encounters an impact load or the drive mechanism is “stuckâ€, causing a sudden increase in the motor current;
â— The second is a short circuit on the output side of the inverter. If the output line from the output terminal to the motor is short-circuited to each other, or a short circuit occurs inside the motor, grounding (motor burnout, insulation degradation, contact caused by cable damage, grounding, etc.);
â— The third is that the inverter itself is not working properly. For example, two inverter devices of the same bridge arm in the inverter bridge are abnormal during the alternate work.
If the ambient temperature is too high, or the inverter components themselves are aging, etc., the parameters of the inverter are changed, resulting in one device being turned on during the alternation process, and the other device is still turned off in the future, causing The "straight through" of the upper and lower devices of the same bridge arm causes the short-circuit state between the positive and negative terminals of the DC voltage.
(2) Over-current when the speed is increased or decreased: When the inertia of the load is large, and the speed-up time or the speed-down time is set too short, it will cause overcurrent.
During the speed increase process, the operating frequency of the inverter rises too fast, the synchronous speed of the motor rises rapidly, and the rotational speed of the motor rotor cannot keep up due to the large inertia of the load. As a result, the rising speed current is too large; during the speed reduction process, The deceleration time is too short, the synchronous rotation speed drops rapidly, and the rotor of the motor maintains a high rotation speed due to the inertia of the load. At this time, the speed of cutting the magnetic lines of the rotor winding can also be too large to generate an overcurrent.
2.2 Processing methods
(1) At the start of the start, it will trip at a rising speed. This is a phenomenon in which the overcurrent is very serious. The main inspection is:
â— The working machine is stuck;
â— Is there a short circuit on the load side, check if there is a short circuit to the ground with a megohmmeter;
â— Whether the inverter power module is damaged;
â— The starting torque of the motor is too small and the drag system cannot turn.
(2) It does not trip immediately when starting, but trips during operation, mainly check:
â— The speed increase time setting is too short to lengthen the acceleration time;
â— The deceleration time setting is too short to lengthen the deceleration time;
â— The torque compensation (U/f ratio) setting is too large, causing the no-load current to be too large at low frequencies;
â— The electronic thermal relay is not properly set, and the operating current is set too small, causing the inverter to malfunction.
3 overload protection and cause analysis
The motor can rotate, but the operating current exceeds the rated value, called overload.
The basic reflection of the overload is that although the current exceeds the rated value, the magnitude of the excess is not large, and generally no large inrush current is formed.
The output current exceeds the inverse time characteristic overload current rating, the protection function operates, and the capacity of the inverter is too small.
3.1 The main cause of overload
(1) Mechanical overload: The main feature of excessive load is that the motor is hot and can be found by reading the operating current from the display.
The main reason is that the inverter load is too large, the acceleration/deceleration time and the running cycle time are too short; the voltage of the V/F characteristic is too high; the inverter power is too small.
(2) Three-phase voltage imbalance: causing the operating current of a certain phase to be too large, resulting in overload tripping. It is characterized by uneven heating of the motor. It is not always found when reading the running current from the display screen (since the display only shows one Phase current).
(3) Malfunction: The current detection part inside the inverter has a fault, and the detected current signal is too large, causing a trip.
3.2 Inspection method
(1) Check if the motor is hot
If the temperature rise of the motor is not high, first check the load size, acceleration and deceleration time, whether the operation cycle time setting is reasonable, and correct the V/F characteristics, check whether the electronic thermal protection function of the inverter is preset properly, such as frequency conversion. If there is still a margin, the preset value of the electronic thermal protection function should be relaxed; if the allowable current of the inverter has no margin, it can no longer be relaxed, and according to the production process, the overload that occurs is a normal overload, indicating the inverter If the choice is not correct, the capacity of the inverter should be increased and the inverter replaced.
This is because, when the motor is dragging the variable load or the intermittent load, as long as the temperature rise does not exceed the rated value, it is allowed to be overloaded for a short time (a few minutes, or even tens of minutes), and the inverter does not allow it.
If the temperature rise of the motor is too high and the overload that occurs is a normal overload, it means that the load of the motor is too heavy.
At this time, first consider whether the gear ratio can be appropriately increased to reduce the load on the motor shaft.
If it can be increased, increase the transmission ratio; if the transmission ratio cannot be increased, increase the capacity of the motor.
(2) Check if the three-phase voltage on the motor side is balanced
If the three-phase voltage on the motor side is unbalanced, check whether the three-phase voltage at the output of the inverter is balanced. If it is unbalanced, the problem is inside the inverter. Check the inverter module and its drive circuit of the inverter; The voltage at the output is balanced, and the problem occurs on the line from the inverter to the motor. Check that all the screws on the terminals are tightened. If there is a contactor or other electrical device between the inverter and the motor, Check that the terminals of the appliance are tight and that the contact is in good condition.
If the three-phase voltage on the motor side is balanced, the operating frequency at the time of tripping should be known: if the operating frequency is low and vector control is not used (or no vector control), the U/f ratio is first reduced, and if the load is still reduced, the load can still be driven. , the original U/f ratio is too high, the peak value of the excitation current is too large, and the current can be reduced by lowering the U/f ratio; if the load is reduced after the reduction, the inverter should be considered. Capacity; if the frequency converter has vector control, vector control should be used.
(3) Check if it is malfunctioning
After the above checks, if no cause is found, it should be checked whether it is a malfunction.
The method of judging is to measure the output current of the inverter with an ammeter under light load or no load, and compare it with the running current value displayed on the display. If the current reading displayed by the display is larger than the actual measured current. If there is more, it means that the current measurement part of the inverter has a large error, and the "overload" trip may be a malfunction.
4 undervoltage protection LU
Undervoltage is also a problem we often encounter in use.
After the power supply voltage is lowered, if the DC voltage of the main circuit falls below the undervoltage detection value, the protection function operates.
In addition, if the voltage falls below the operation of the inverter control circuit, all protection functions are automatically reset (detected value: DC400V).
When an undervoltage fault occurs, first check whether the input power supply is out of phase. If there is no problem with the input power supply, check the rectifier circuit for any problems. If there is no problem, then look at the DC detection circuit for any problems.
If the main circuit voltage is too low (380V series is lower than 400V), the main reason is that one of the rectifier bridges is damaged or one phase of the thyristor three-phase circuit is not working properly, which may lead to the occurrence of undervoltage faults. Secondly, the main circuit breaker If the contactor is damaged, the DC bus voltage loss may cause undervoltage on the charging resistor.
If the voltage detection circuit fails, the undervoltage problem occurs. The DC end of the main circuit (between P and N) exceeds the detection value due to malfunction of the inverter or malfunction caused by noise, so contact the manufacturer.
5 Overvoltage protection OUd
The regenerative current from the motor increases, and if the DC voltage of the main circuit exceeds the voltage detection value, the protection function operates when an excessive voltage is applied erroneously (detected value: DC750V).
There are three main types of overvoltage protection: overvoltage during acceleration, overvoltage during deceleration, and overvoltage at constant speed.
Overvoltage alarms generally occur when the machine is stopped. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and the brake unit.
The overvoltage of the inverter is concentrated on the voltage of the DC bus.
Under normal circumstances, the inverter DC power is the average value after three-phase full-wave rectification.
If calculated with a line voltage of 380V, the average DC voltage Ud=1.35UL=513V.
When the overvoltage occurs, the storage capacitor of the DC bus will be charged. When the voltage is up to 760V, the inverter overvoltage protection action.
Therefore, the frequency converter has a normal operating voltage range, which is likely to damage the frequency converter when the voltage exceeds this range.
The common overvoltage is mainly the overvoltage during power generation braking. The probability of occurrence is higher, mainly because the synchronous speed of the motor is higher than the actual speed, so that the motor is in the power generation state, and the inverter does not have the brake unit installed. There are two situations that can cause this failure.
(1) When the inverter drags the large inertia load, its deceleration time is set relatively small. During the deceleration process, the output speed of the inverter is faster, and the resistance deceleration is slower due to the load characteristic itself, so that the load drags the motor. The speed is higher than the speed corresponding to the frequency output of the inverter. The motor is in the power generation state, and the inverter has no energy feedback unit. Therefore, the DC link voltage of the inverter rises and exceeds the protection value, causing a fault.
Such faults in paper machines often occur in the dry part. To handle such faults, the regenerative braking unit can be increased, or the inverter parameters can be modified to set the inverter deceleration time to be longer.
The added regenerative braking unit has energy consumption type, parallel DC bus absorption type and energy feedback type.
The energy consumption type connects a braking resistor in parallel with the DC link of the inverter, and controls the on/off of the power tube by detecting the DC bus voltage.
The parallel DC bus absorption type is used in a multi-motor transmission system. Such a system often has one or several motors that are often operated in a power generation state to generate regenerative energy that is absorbed by the motor in an electric state through the parallel bus.
The energy feedback type inverter-side converter is reversible, and the inverter can return the regenerative energy to the grid when regenerative energy is generated.
(2) This fault may also occur when multiple motors are dragging the same load, mainly due to no load distribution.
Taking two motors to drag a load as an example, when the actual rotational speed of one motor is greater than the synchronous speed of the other motor, the motor with a high rotational speed is equivalent to the prime mover, and the low rotational speed is in a power generating state, causing a malfunction.
6 Other protection
6.1 Overheating OH4
Overheating is a malfunction that is often encountered.
When this happens, first think about whether the cooling fan is running. Observe the outside of the machine to see if the fan is running. In addition, for the machine above 30kW, there is also a cooling fan inside the machine. The damage of this fan will also cause OH4 alarm.
According to the set value of L1-04, the inverter stops outputting, when the motor overheats, correct the load size, acceleration/deceleration time, and operation cycle time; correct the V/F characteristics; confirm the motor temperature input from terminals A1/A2.
6.2 Ground Fault GF
The ground fault is also a fault that is often encountered. The ground current on the output side of the inverter exceeds 50% of the rated output current of the inverter. The main reason is that a short circuit has occurred on the output side of the inverter (burning of the motor, deterioration of insulation, damage of the cable). Contact, grounding, etc.).
In addition to the cause of the problem of motor grounding, the most likely part of the fault is the Hall sensor. Due to the influence of environmental factors such as temperature and humidity, the Hall is prone to drift, resulting in GF alarm.
For Yaskawa inverters, if the fast-melting is not burned out, the optocoupler on the trigger board needs to be repaired; if the fast-melting burns out, the module needs to be replaced, fast-melted, and the optical coupling on the trigger board needs to be repaired.
6.3 Motor does not rotate
(1) Even if the RUN button of the operator is pressed, the motor does not turn. In this case, the following reasons can be considered: The setting of the operation method is incorrect.
(Selection of operation command) When b1-02=1 (control circuit terminal), even if the RUN button is pressed, the motor does not run. Press the LOCAL/REMOTE button to switch to the operator or set b1-02=0 (operation Device).
The frequency command is too low: when the frequency command is lower than the frequency set by E1-09 (lowest output frequency), the inverter cannot run, and the frequency command is changed to be greater than the lowest frequency.
(2) Even if the external operation signal is input, the motor does not turn. The important reason is that the inverter is not in the drive mode and the inverter is in the ready state and cannot be started.
Press the MENU button, the DRIVE LED flashes, and then press the DATA/ENTER button to enter the drive mode.
Entered the drive mode, the DRIVE LED lights up.
(3) When accelerating and connecting the load, the motor stops and the load is too large.
Although the inverter has a stall prevention function and a fully automatic torque boost function.
However, if the acceleration is too large and the load is too large, the response limit of the motor is exceeded. Please extend the acceleration time and reduce the load.
In addition, you can also consider increasing the power of the motor.
(4) The motor can only be turned in one direction.
Inverted selection is selected. When b1-04 (selection prohibit reverse)=1 (reverse inversion is prohibited), the inverter does not accept the reverse command.
When using both forward and reverse directions, set b1-04=0 (can be reversed).
7 Conclusion
This paper summarizes the protection functions of several alarms and trips of general-purpose inverters. It provides a reference for the reasons for display analysis and finds solutions for the maintenance personnel to judge the inverter faults and maintenance methods.
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