Causes and solutions for inverter low voltage tripping

Reasons for inverter low voltage tripping

The low voltage of the inverter mainly refers to the low voltage of the intermediate DC circuit. Generally, the reasons that can cause the low voltage of the intermediate DC circuit come from two aspects:

1. Low voltage from the power input side

Under normal circumstances, the power supply voltage is 380V, with an allowable error of -15%~10%. After three-phase bridge full-wave rectification, the intermediate DC voltage is 513V. In some cases, a small voltage fluctuation in the power line voltage will not cause the inverter to trip under low voltage. Only when the effective value of the grid voltage is between 80%~85% of the rated value and lasts for more than one cycle will the inverter be triggered. The low voltage on the power input side is mainly due to fluctuations in the grid voltage or switching of the main power line, lightning strikes that affect the amplitude of the power supply sine wave, overload of the power plant's own transformer or unbalanced load, etc.

2. Low voltage from the load side

The main reasons for this are the startup and application of large equipment, line overload or starting of large motors, etc. The frequency converter is composed of two parts: a rectifier and an inverter. Through the study of frequency converters, low voltage of the frequency converter refers to the low voltage of the intermediate DC circuit (that is, the input voltage of the inverter is too low). General frequency converters have protection functions for overvoltage, loss of voltage and instantaneous power failure. The inverter device of the frequency converter is divided into two types: GTR and IGBT. When the inverter device of the frequency converter is GTR, once the voltage is lost or the power is cut off, the control circuit will stop outputting signals to the drive circuit, so that the drive circuit and GTR will all stop working, and the motor will be in a free braking state. When the inverter device is IGBT, after the voltage is lost or the power is cut off, the frequency converter will be allowed to continue working for a short time td. If the voltage is lost or the power is cut off for totd, the frequency converter will stop running for self-protection. Generally, td is 15-25ms, and the power supply "shaking" time to is generally more than a few seconds. The frequency converter will stop running for self-protection, so that the motor will stop running. Therefore, solving the problem of inverter low voltage tripping cannot start from the inverter's inherent time td and voltage loss time to, but must start from the amplitude that can withstand the voltage drop.

Solution to inverter low voltage tripping

To solve the problem of low voltage tripping of the inverter, we must master two key points:

First, you need to choose a frequency converter with IGBT inverter devices;

The second is to choose a frequency converter that can still work normally under conditions 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 excess is not large and generally does not form a large impact current.

Causes and inspection methods of inverter overload tripping

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, resulting in tripping.

2. The mechanical load is too heavy. The main characteristic of overload is the heating of the motor, which can be discovered by reading the operating current on the display screen.

3. The three-phase voltage is unbalanced, causing the operating current of one phase to be too large, resulting in overload tripping. Its characteristic is uneven heating of the motor, which may not be found when reading the operating current from the display screen (because the display screen only shows one-phase current).

2. How to check 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, check whether the three-phase voltage at the inverter output end is balanced. If it is also unbalanced, the problem is inside the inverter.

If the voltage at the inverter output end is balanced, the problem lies in the line from the inverter to the motor. Check whether the screws of all the terminals are tightened. If there are contactors or other electrical appliances between the inverter and the motor, check whether the terminals of the relevant appliances are tightened and whether the contact conditions of the contacts are good.

If 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 is not used (or there is no vector control), first reduce the U/f ratio. If the load can still be driven after the reduction, it means that the original preset U/f ratio is too high and the peak value of the excitation current is too large. The current can be reduced by reducing the U/f ratio;

If the load cannot be carried after reduction, you should consider increasing the capacity of the inverter; if the inverter has vector control function, vector control should be adopted.

2. Check whether the motor is hot. If the temperature rise of the motor is not high, first check whether the preset value of the electronic thermal protection function of the inverter is reasonable. If the inverter still has 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 that occurs is a normal overload, it means that the motor is overloaded. At this time, first of all, whether the transmission ratio can be appropriately increased to reduce the load on the motor shaft should be increased. If it can be increased, then increase the transmission ratio. If the transmission ratio cannot be increased, then increase the capacity of the motor.