When we need to choose the right type of variable-frequency drive (VFD), we need to decide which control method VFD is most suitable, depending on the type of production machinery, the speed range, the static speed accuracy and the starting torque required. The so-called suitable, is both good and economic, to meet the basic conditions and requirements of technology and production.
I. How to choose VFD power.
The system efficiency is equal to the product of the VFD efficiency and the motor efficiency. The system efficiency is only higher when both are working at a higher efficiency. From the point of view of efficiency, the following points should be noted when choosing the VFD power.
1) VFDs are most suitable when the power value is equal to the motor power value so that the VFD can operate at a higher efficiency value.
2) When the power classification of the VFD is different from that of the motor, the power of the VFD should be as close to the power of the motor as possible, but slightly greater than the power of the motor.
3)When the motor is frequently started, braked or started under heavy load and works frequently, a higher class VFD can be selected to utilise the VFD for long term safe operation.
4)After testing, the actual power of the motor does have a surplus, so a VFD smaller than the power of the motor can be considered, but attention should be paid to whether the instantaneous peak current will cause overcurrent protection.
5) When the VFD is different from the motor power, the setting of the energy saving program must be adjusted accordingly to achieve a higher energy saving effect.
II. How to choose the right box structure for the VFD.
The cabinet structure of the VFD has to be adapted to the environmental conditions, i.e. temperature, humidity, dust, pH, corrosive gases, etc. must be taken into account. There are several common types of structure for users to choose from.
1) Open IPO type without case, suitable for installation in electrical control boxes or electrical rooms with screens, trays and racks, especially when multiple VFDs are used centrally. It is better to choose this type, but with high environmental conditions;
2) Enclosed IP20 type is suitable for general use and can be used where the amount of dust is low or where the temperature and humidity are low;
3) Enclosed IP45 is suitable for use in poor industrial site conditions;
4) Enclosed IP65 is in harsh environmental conditions with water, dust and some corrosive gases.