Inverter maintenance science: what is over-temperature protection?

Inverter maintenance science: what is over-temperature protection?

When we repaired the frequency converter (VFD), we found that the temperature protection function is an indispensable condition to ensure the stable operation of the VFD. Today, let’s talk about common VFD faults and their solutions. Today’s topic is “over temperature protection”.

1. VFD over temperature protection and its necessity

The temperature protection function of the VFD is an indispensable condition to ensure the stable operation of the High-performance General Vector Inverter XCD-E5000. In VFD main circuit power devices, rectifier bridges and inverter bridges are all semiconductor power devices, and due to the limitation of their operating temperature characteristics, the allowable operating range of the device cannot be exceeded. In addition, the temperature is not allowed to be too high in the electronic circuit of the VFD. If the VFD is overheated, it may cause the performance of the whole machine to decline, the device to age, or even the machine to explode, so temperature protection is essential.
2. VFD temperature detection

① Usually High-performance General Vector Inverter XCD-E5000 detects the intake air temperature, which can be understood as the ambient temperature; the temperature of the radiator near the rectifier bridge, and the temperature and power of the radiator near the inverter bridge are different at different detection points.

②VFD has passed the thermal balance check at the beginning of research and development, that is, the heat generated by the VFD under the rated load is balanced with the heat dissipation of the VFD, that is to say, the VFD will work under normal working conditions, and the VFD will not overheat.

3. Improper design and selection lead to excessive temperature.

① The capacity of the VFD does not match the power of the drive motor, resulting in a large operating current. zui eventually leads to VFD over temperature protection.

② The VFD selection margin is insufficient, and the load fluctuation and overload repetition period are not fully considered.

③ VFD is used in high-altitude areas, and the use of VFD for capacity reduction is not fully considered. The reason is that in high-altitude areas, the air is thin, which will cause the VFD’s cooling effect to deteriorate. (Of course, the temperature in high-altitude areas is lower than that in low-altitude areas, which is conducive to VFD heat dissipation).

④ Long-term low-frequency operation of the VFD leads to an increase in the switching loss of the VFD itself, resulting in over-temperature of the VFD. In this case, it is necessary to increase the working frequency of the VFD and increase the reduction ratio of the transmission mechanism.

⑤ When the ambient temperature is high, the heat dissipation capacity of the VFD is poor. It is necessary to consider installing an air conditioner in the VFD cabinet for heat dissipation, or consider installing an air conditioner in the electric control room as a whole.

4. Over temperature caused by VFD itself

①The temperature detection circuit is abnormal, resulting in over temperature.

②The temperature sensor is damaged, causing the temperature to be too high.

③ The VFD’s own cooling fan is damaged, and the DC24V fan power supply is abnormal, causing the VFD to overheat.

④ For high-power VFD, improper selection of the tap voltage of the cooling fan power transformer winding leads to low fan speed, which cannot meet the needs of normal ventilation.

High-power VFD, the cooling fan power transformer fuse is blown, and the cooling fan does not rotate.

5. The improper molding of the cabinet causes the temperature to be too high.

①The installation space of the VFD in the cabinet has not been fully considered, and sufficient cooling space should be reserved according to the VFD hardware manual.

②The ventilation of the inverter cabinet is not enough, so the heat generated by the VFD cannot be taken away by the air.

③ The structure of the frequency conversion cabinet is unreasonable. Normally, cold air enters from the lower part of the inverter cabinet, and hot air is exhausted from the top. Air ducts are generally designed according to the natural flow of air.

Multiple sets of VFDs are installed in the cabinet, and the VFDs are arranged one above the other, causing the above VFD overtemperature fault.

6. Improper use leads to high temperature.

① In the installation environment of VFD, there is a lot of oil, gas and dust in the air. After working for a long time, it is equivalent to coating a layer of oil on the surface of the radiator of the VFD, which is very unfavorable for heat dissipation. It is necessary to install filter cotton at the air inlet of the VFD cabinet.

Post time: Sep-24-2022