As anyone who does a motor knows, frequency conversion motor has two aspects that are completely different from ordinary motors: first, insulation structure; Second, ventilation and heat dissipation. The insulation structure mainly strengthens the insulation between the turns of the armature winding for the high frequency shock wave, and the ventilation and heat dissipation structure has many strange shapes due to the different motor structure, use occasions and working modes. Here, Ms. Lent students to answer questions and explain the topic, and discussed the ventilation and heat dissipation of the motor under the condition of frequency conversion power supply. The above-mentioned empty shell air hood or air hood with blades and small motor are only several typical structures of external forced air cooling of variable frequency motor. They are two types of fans -- ordinary axial fan and knapsack fan, which are used for enclosed motor due to size limitation.

Frequency conversion motor is divided into closed type and open protection type according to structure. Closed frequency conversion motors with protection grade IP44 and above are generally equipped with forced air cooling fans. Some products with narrow speed range and high speed lower limit have their own fans.

Open the protective variable frequency motor because the variable frequency motor due to the armature winding and the ambient air directly heat exchange, speed lower limit is not less than 50%~70% of the rated speed, generally only a little special electromagnetic design can meet the requirements of operating conditions; However, the motor with very high power density must also be equipped with forced air cooling fan, and sand prevention measures should be taken in the application of sand environment.

According to the use of the most common motor fan, we can be divided into two categories, namely axial flow fan and centrifugal fan, but the two in addition to the appearance of the inconsistent, and what will be the difference?

The difference between mechanism and performance parameters

● Fluid direction. Axial flow fan wind along the fan blade axial flow, centrifugal is the wind from the fan axial suction using centrifugal force thrown out from the circumferential direction.

Low parameters. Axial flow fans have large flow and small wind pressure, while centrifugal fans have large wind pressure and small flow.

● Airflow direction. The flow direction of the axial fan is perpendicular to the rotation direction of the blade, and the flow direction of the centrifugal fan is tangent to the rotation direction of the blade.

● Performance comparison. Compared with the axial flow fan, the biggest disadvantage of centrifugal fan is large volume, but the open protective variable frequency motor must use centrifugal fan, and match the wind resistance of the motor inner cavity. Because of their different structures, in the case of the same air volume and the same wind pressure, the power consumption of the centrifugal fan is much larger than that of the axial flow fan, but the noise will be relatively small. Usually, axial flow fans are used in fire fighting and tunnel ventilation, and centrifugal fans are preferentially used in high-grade buildings of hotels.

Structural differences

● Centrifugal fan medium flow, and axial flow fan medium flow;

● Centrifugal fan installation is more complex, axial flow fan installation is simple;

● Centrifugal fan motor and wind wheel through the shaft connection, axial flow fan and motor is usually integrated structure;

● Centrifugal fans are often installed in the inlet and outlet, such as air conditioning, boiler blower and induced draft fan, axial flow fan is often installed in the air duct, or the front end of the outlet.

Why do variable frequency motors use axial flow fans

Ordinary motor for constant frequency and constant voltage power supply, constant speed, ventilation and heat dissipation in a stable state. The frequency conversion motor is specially designed for the operation condition of frequency conversion and voltage variation. On the one hand, the current is non-sinusoidal, and the harmonic components generated by the frequency converter lead to the increase of copper consumption of the motor stator and rotor. On the other hand, when the frequency is low, the loss ratio caused by the current high harmonic increases, while the cooling air volume decreases by the cubic ratio of the speed, which makes the cooling condition of the motor deteriorate at low speed and the temperature rise sharply. Therefore, the cooling effect of the inverter motor with its own fan is far from meeting the heat dissipation requirements of the motor, and forced independent ventilation must be adopted, that is, equipped with an independent fan.

When frequency conversion motor is used, the sequence principle of frequency converter and motor starting is that the axial fan should be started before the motor power is turned on to ensure the cooling requirements of the motor. In the shutdown, first shut down the motor, and then shut down the fan, in order to prevent the axial flow fan does not open the motor independent operation of the motor due to heat burn, which is also in the use of some low-end users often occur in the process of the problem.

Another problem is that if the axial fan and the motor share the same power supply, when the motor is used by frequency conversion, the axial fan motor will also be used by frequency conversion, and the motor supporting the fan will suffer the same damage fate. The cooling effect on the main motor is not achieved, and the fan itself cannot escape the bad fate.

Why do some motors use backpack fans

Some customers require the motor to install additional devices such as encoder and overspeed opening, which will lead to the insufficient axial space of the motor's non-axial extension end. In order to control the axial size of the motor and the cooling requirements of the motor, the backpack fan is selected. According to the performance characteristics of the fan, the backpack fan is a combination of centrifugal fan and motor wind hood.