Induction motors are asynchronous motors with a squirrel-cage rotor. Their magnetic field is created by induced currents in the rotor windings (Faraday’s law of induction). Due to this technology, the rotor is not synchronised with the rotating magnetic stator field. The higher the load, the higher the slip and the higher the motor torque.
For HVAC applications like fans and centrifugal pumps, V/f frequency inverters can be used to regulate motor speed. The frequency will keep the ratio between voltage and frequency constant. As a result, the motor flux is kept constant to prevent the magnetic field from weakening and to assure sufficient motor torque.
Induction motors are the standard for most industrial applications. In the HVAC industry, induction motors are typically used in larger installations. Worldwide, electric motors consume approximately 60 % of the total energy required. That is why a lot of time and energy has been invested during recent years on making electric motors more energy efficient. Under the influence of the Energy efficiency guidelines, significant energy savings have been achieved. The energy efficiency of induction motors is defined in the standard IEC 60034 30-1. This information is usually marked on the motor name plate. The following international classifications are defined:
- IE1 - Standard Efficiency
- IE2 - High Efficiency
- IE3 - Premium Efficiency
- IE4 - Super premium Efficiency (PMSM)
- IE5 - Ultra-premium Efficiency (PMSM)
The major difference between these variants is the energy consumption. In many cases, more copper is used to minimise losses, in some IE3 motors the complete rotor is made in copper. This has an important impact on the price of the motor.