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Viewing and handling methods of inverter overload

Jan 16, 2021

Viewing and handling methods of inverter overload


The output current of the inverter continues to cross the rated current, but has not yet crossed the transient overcurrent point, usually the continuing time is defined as 1min. Regarding the constant torque inverter, the usual overload is 150% for 1min, and the variable torque inverter is usually 10%-120%/1min. It is assumed that the motor and the inverter are adapted, and the overload of the motor is stronger than the inverter. The overload at this time is called the inverter overload. The reference current is the inverter rated current; assuming that the motor rated current is less than the inverter rated current, input accurately After the motor nameplate and maintenance points, the overload maintenance is usually called motor overload maintenance. Therefore, the details of maintenance at the time must be different. Since the overload point of the inverter is not far from the overcurrent point of the inverter, these two maintenance and replacement actions are often used.

The overload at the time of recommendation usually presents the following two situations


1. The load static torque is large, the low frequency output of the inverter is not good, so it is locked or rotating at low speed. The factors may include: the low frequency torque difference of the inverter, the suggested frequency can be corrected (small plan correction, usually within 5Hz), torque trek or correction Select the vector inverter


2. The external motor is recommended to rotate at high speed, and the solution: use other suggested methods or brake first.


The primary factor of acceleration and deceleration overload is: the stator and rotor slip changes too much


1. Reduce the acceleration and deceleration time and reduce the rate of stator change


2. Participate in the brake unit or correct the brake utilization rate


3. Such as vector control inverter, speed loop PID parameters can be corrected


Constant speed overload


1. Assuming it is a single transmission, the load is not firm, it is a good way to check the machine


2. Assuming that it is multi-drive, it may be other machinery that affects the operation of the equipment. Please check the cooperation and synchronization between systems.


Check method


(1) Check if the motor is hot


Assuming that the temperature rise of the motor is not high, the first step is to check whether the preset electronic thermal maintenance function of the frequency converter is reasonable. If the frequency converter still has a margin, the preset value should be relaxed; if the allowable current of the frequency converter is no longer available The margin cannot be relaxed any more, and according to the production technology, the overload presented is attributed to the normal overload, which clarifies that the selection of the frequency converter is improper, and the capacity of the frequency converter should be increased and replaced. This is because when the motor is dragging to change the load or the intermittent load, only the temperature rise does not exceed the rated value, and short-term (a few minutes or a few minutes) overload is allowed, but the inverter does not allow it. Assuming that the temperature rise of the motor is too high, and the overload presented is attributed to the normal overload, it is stated that the load of the motor is too heavy. At this time, we should first consider whether the transmission 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, the capacity of the motor should be increased.


(2) Check whether the three-phase voltage on the motor side is balanced


Assuming that the three-phase voltage on the motor side is unbalanced, you should check whether the three-phase voltage at the output of the inverter is balanced. If it is unbalanced, the question is inside the inverter. You should check the inverter module and its drive circuit.


If the voltage at the output terminal of the frequency converter is balanced, it is suspected that on the line from the frequency converter to the motor, check whether all the screws on the terminals are tightened. Assuming that there is a touch device or other electrical appliances between the inverter and the motor, you should also check whether the terminals of the electrical appliances have been tightened, and whether the touch of the contacts is excellent.


Assuming that the three-phase voltage on the motor side is balanced, the operating frequency at the time of tripping should be understood: if the operating frequency is low and vector control (or no vector control) is used, the U/F ratio should be lowered first; Load, it clarifies that the preset U/F ratio is too high and the peak value of the excitation current is too large. The current can be reduced by decreasing the U/F ratio; assuming that the load cannot be driven after the drop, consider increasing the frequency conversion The capacity of the inverter; assuming that the inverter has a vector control function, the vector control method should be selected.


(3) Check if it is a malfunction


When no element is found after the above inspection, it should be checked whether it is a malfunction. The method of difference is to use an ammeter to measure the output current of the inverter under light load or no load, and compare it with the operating current value flashed on the flashing screen. It is assumed that the flashing current reading on the flashing screen is larger than the current measured in practice. If there are more, it means that the current measurement inside the frequency converter is somewhat faulty, and the "overload" trip may be a malfunction.