The rotating speed of an electric motor can be controlled by frequency inverter. This variable rotating speed control provides many advantages such as optimization of production processes and energy saving. The speed and the power needed to drive the driven equipment can be tailored more accurately when a frequency inverter is utilized. Frequency inverter driven motors consume less energy than fixed speed drives with a different way of control.
Pumps and fans are the best known applications where energy can be saved. It is often the case that the airflow delivered by a fan is greater then actually needed at certain times and the airflow needs to be throttled when a fan is driven by fixed speed motor. If the motor is frequency inverter driven, the airflow can be controlled much more economically by regulating the motor speed. If an electric motor is connected to a frequency inverter, no restrictions apply when the speed control range is between 30% to 120% of the rated speed (at 50 Hz). A condition for a constant torque application is constant cooling. A cooling fan is fitted on the back motor shaft in standard IC411 electric motors. By control also effects the cooling capacity of the electric motor. The cooling effect decreases to the third power as the the motor speed is lowered. The motor torque will have to be derated as much as 1/3 of the rated torque in the lower control range. To prevent this an independently driven fan can be mounted, IC 416, forced cooling. The rated torque is then available throughout the speed control range. The power (torque) reduction of the driven equipment must correspond with the characteristics of the frequency inverter and electric motor combination. For use outside this control range please consult the electric motor manufacturer.
The type of insulation that is applied when using a frequency inverter is called a Pulse Modulated winding, or the PM winding. Voltage peaks occur during frequency control, which affect the insulation material of the motor winding in the negative way. The standard rotor nl® electric motors are resistant to voltage peaks up to 1,500 V. The use of the PM winding is advisable for rated voltages higher than 500 V combined with inverter control. The PM winding can handle voltage peaks up to 2,250 V. The PM winding, however, affects the Power Output. As the insulation material is thicker and less copper fits in the stator slots which effects the electric motor's characteristics.