Reasons for inverter low voltage trip

1. The low voltage of the inverter mainly refers to the low voltage of the intermediate DC circuit. Generally, the reason for the low voltage of the intermediate DC circuit comes from two aspects:

(1) Low voltage from the power input side

Under normal circumstances, the power supply voltage is 380V, and the allowable error is -15%~10%. After three-phase bridge full-wave rectification, the intermediate DC voltage value is 513V. In some cases, the power line voltage is small and the voltage fluctuation will not be The low voltage trip of the inverter will only cause the inverter to operate if the effective value of the grid voltage is between 80% and 85% of the rated value and the duration exceeds one cycle. The low voltage on the input side of the power supply is mainly due to the fluctuation of the grid voltage or the switching of the main power line, the power supply sine wave amplitude is affected by the lightning strike, the transformer of the power plant itself is overloaded or the load is unbalanced, etc.

(2) Low voltage from the load side

The reasons for this are mainly the start-up and application of large equipment, line overload, or starting large motors. The frequency converter is composed of rectifier and inverter. Through the research of the inverter, the low voltage of the inverter refers to the low voltage of the middle DC loop (that is, the input voltage of the inverter is too low). General frequency converters have protection functions of overvoltage, loss of voltage and instantaneous power failure. The inverter device of the inverter is divided into GTR and IGBT. When the inverter device of the inverter is GTR, once the voltage is lost or the power is cut off, the control circuit will stop outputting the signal to the drive circuit, so that the drive circuit and GTR all stop working, the motor It will be in free braking state. When the inverter device is IGBT, after the voltage loss or power failure, the inverter will be allowed to continue to work for a short time td. If the voltage loss or power failure time is totd, the inverter will protect itself and stop running. Generally, td is between 15 and 25 ms, and the power supply “shaking” time is generally more than a few seconds. The inverter will protect itself and stop running, so that the motor stops. Therefore, to solve the problem of inverter low voltage trip can not start from the inverter's inherent time td and voltage loss time to, but must start from the amplitude of the voltage drop.

2. Solutions for inverter low voltage trip:

There are two key points to be solved to solve the problem of inverter low voltage trip:

(1) It is necessary to select the inverter with IGBT inverter device;

(2) It is necessary to select the inverter that can still work normally under the condition of large voltage loss.

The motor can rotate, but the running current exceeds the rated value, which is called overload. The basic reflection of overload is that although the current exceeds the rated value, the magnitude of the excess is not large, and generally a large inrush current is not formed.

The reason and inspection method of inverter overload trip

1. The main reason for inverter overload

(1) Malfunction, the current detection part inside the inverter fails, and the detected current signal is too large, causing a trip.

(2) The mechanical load is too heavy. The main feature of the heavy load is that the motor heats up and can be found by reading the running current from the display.

(3) The three-phase voltage is unbalanced, which causes the operating current of a certain phase to be too large, resulting in overload tripping. It is characterized by unbalanced motor heating, which may not be found when the operating current is read from the display (because the display only shows one Phase current).

2. Check method of whether the inverter is overloaded

(1) 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 on the output side of the inverter is balanced. If it is not balanced, the problem is within the inverter.

If the voltage at the output of the inverter is balanced, the problem lies in the line from the inverter to the motor. Check whether the screws of all terminals are tightened. If there is a contactor or other electrical appliances between the inverter and the motor, It should be checked whether the terminals of the related electrical appliances have been tightened and the contact conditions of the contacts are good.

If the three-phase voltage on the motor side is balanced, you should understand the operating frequency at the time of tripping: if the operating frequency is low and vector control (or no vector control) is not used, first reduce the U/f ratio, if it can still drive the load , It means that the original preset U/f ratio is too high, the peak value of the excitation current is too large, and the current can be reduced by reducing the U/f ratio;

If the load can not be moved after the reduction, you should consider increasing the capacity of the inverter; if the inverter has vector control function, the vector control method should be used.

(2) Check whether the motor heats up. If the temperature rise of the motor is not high, first check whether the electronic thermal protection function of the inverter is preset properly. If the inverter still has a margin, the preheating of the electronic thermal protection function should be relaxed. Set value.

If the temperature rise of the motor is too high, and the overload is normal overload, it means that the motor is overloaded. At this time, whether the transmission ratio should be properly 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.