Continuous duty application
The achievable energy savings from one energy efficiency class to the next higher are about 15 to 20% reduction in the losses. The payback time of extra investment costs related to high or premium efficient motors can easily be calculated taking the overall motor efficiency and energy cost into account.
The following diagram illustrates the energy savings in percent of the consumed electrical energy of the motor in relation to the rated motor output power when upgrading from a lower IE class to a higher one.
Saved Energy Consumption 50 Hz [% of Input Energy]
IE1 to IE2 IE1 to IE3 IE1 to IE4
10 Rated Motor Power [kW]
Potential energy savings by improvement of efficiency-classes
An injection of DC into the stator windings will create a retarding torque to bring the motor to a stop. The highest braking torque is typically reached at a speed of 10 to 20% of rated speed. If full-load current is applied in DC injection braking, the time should be limited to 5 minutes per hour without consulting the motor manufacturer. It is recommended that the motor have over-temperature protection.
During DC injection braking motor heating takes place approximately proportional to the square of the current while applied. This heating (energy dissipation) must be included in the duty cycle analysis for intermittent duty applications.
Applications involving load cycling
Some applications require running at some load for a period of time followed by a period during which no useful work is being done by the driven machine. In this case energy could be saved by stopping and de-energizing the motor and restarting it at the beginning of the next load period.