1. Overcurrent Tripping and Cause Analysis Overcurrent tripping of frequency converters can be divided into short circuit faults, tripping during operation, and tripping during acceleration and deceleration. 1.1 Short Circuit Fault (1) Fault Characteristics a) The first trip may occur during operation, but if it is reset and restarted, it will often trip as soon as the speed is increased. b) It has a large inrush current, but most frequency converters can perform protection tripping without damage. Because the protection tripping is very fast, it is difficult to observe the magnitude of the current. (2) Judgment and Handling The first step is to determine whether there is a short circuit. To facilitate judgment, before restarting after reset, a voltmeter can be connected to the input side. When restarting, the potentiometer is slowly rotated from zero. At the same time, pay attention to the voltmeter. If the frequency converter trips immediately as soon as the output frequency rises, and the pointer of the voltmeter shows a momentary return to "0", it means that the output terminal of the frequency converter has been short-circuited or grounded. The second step is to determine whether the short circuit is inside the frequency converter or outside. At this point, disconnect the inverter output wiring and then rotate the potentiometer to increase the frequency. If it still trips, it indicates an internal short circuit in the inverter; if it no longer trips, it indicates an external short circuit in the inverter. The wiring between the inverter and the motor, as well as the motor itself, should be checked. 1.2 Light Load Overcurrent Tripping: The load is very light, yet overcurrent tripping occurs. This is a phenomenon unique to variable frequency speed control. In V/F control mode, a prominent problem exists: instability of the motor's magnetic circuit system during operation. The fundamental reason is that at low frequencies, torque compensation (i.e., increasing the U/f ratio, also called torque boost) is often required to drive heavier loads. This causes the saturation level of the motor's magnetic circuit to vary with the load. This overcurrent tripping caused by motor magnetic circuit saturation mainly occurs under low-frequency, light-load conditions. Solution: Repeatedly adjust the U/f ratio. 1.3 Overload overcurrent (1) Fault phenomenon Some production machinery suddenly increases the load during operation, or even "gets stuck". The speed of the motor drops sharply because it cannot be driven, the current increases sharply, and the overload protection cannot act in time, resulting in overcurrent tripping. (2) Solution a) First, find out if the machinery itself is faulty. If it is faulty, repair the machine. b) If this overload is a phenomenon that often occurs in the production process, first consider whether the transmission ratio between the motor and the load can be increased? Appropriately increasing the transmission ratio can reduce the resistance torque on the motor shaft and avoid the situation of not being able to drive. If the transmission ratio cannot be increased, then the only option is to increase the capacity of the motor and the frequency converter. 1.4 Overcurrent during speed increase or decrease This is caused by excessive speed increase or decrease. The following measures can be taken: (1) Extend the speed increase (decrease) time First, find out whether the speed increase or decrease time is allowed according to the production process requirements. If it is allowed, the speed increase (decrease) time can be extended. (2) Accurately preset speed increase (decrease) self-processing (anti-stall) function The inverter is equipped with an overcurrent processing (anti-stall) function for speed increase and decrease. When the speed increase (decrease) current exceeds the preset upper limit current, the speed increase (decrease) will be suspended. When the current drops below the set value, the speed increase (decrease) will continue. 2. Overload trip and cause analysis The motor can rotate, but the operating current exceeds the rated value, which is called overload. The basic reflection of overload is: although the current exceeds the rated value, the excess is not large and generally does not form a large impact current. 2.1 Main causes of overload (1) Excessive mechanical load The main characteristic of overload is that the motor heats up and can be detected by reading the operating current on the display screen. (2) Three-phase voltage imbalance, which causes the operating current of a certain phase to be too large, resulting in overload trip. Its characteristic is that the motor heats up unevenly. It may not be detected when reading the operating current on the display screen (because the display screen only displays the current of one phase). (3) Malfunction: The current detection part inside the inverter malfunctions, and the detected current signal is too large, causing the circuit breaker to trip. 2.2 Inspection method (1) Check if the motor is overheating. If the temperature rise of the motor is not high, first check whether the electronic thermal protection function of the inverter is set reasonably. If the inverter has a margin, the preset value of the electronic thermal protection function should be relaxed. If the temperature rise of the motor is too high and the overload is a normal overload, it means that the motor is overloaded. At this time, first check 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. If the three-phase voltage on the motor side is unbalanced, then check whether the three-phase voltage at the output end of the inverter is balanced. If it is also unbalanced, the problem is inside the inverter. If the voltage at the inverter output is balanced, the problem lies in the wiring between the inverter and the motor. Check that all terminal screws are tightened. If there are contactors or other electrical components between the inverter and the motor, also check that the terminals of these components are tightened and that the contacts are making good contact. If the three-phase voltage on the motor side is balanced, determine the operating frequency at the time of tripping: If the operating frequency is low and vector control is not used (or there is no vector control), first reduce the U/f ratio. If the load can still be driven after reducing the ratio, it indicates that the original preset U/f ratio was too high, and the peak excitation current was too large. The current can be reduced by decreasing the U/f ratio. If the load cannot be driven after reducing the ratio, consider increasing the inverter's capacity. If the inverter has vector control functionality, vector control should be used.