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In 2008, the International Electrotechnical Committee (IEC) published the international standard IEC 60034-30, which outlines a globally harmonized set of energy efficiency classes as well as the energy efficiency requirements for low-voltage three-phase motors.
Electric motors mainly convert electrical energy into mechanical energy in the form of torque and speed. The efficiency rating of this type of motor describes the ratio of usable generated energy to energy consumed. For example, if a motor generates 0.9 kW of mechanical through-drive capability from 1 kW electrical power, it has an efficiency rating of 90%.
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Part 1 of the IEC 60034-30 standard specifies the efficiency ratings or efficiency classes of 1- and 3-phase line motors at 50 and 60 Hz (regardless of the technology). The standard was updated in 2014, and since then the following efficiency classes (IE = International Efficiency) have been defined for asynchronous motors (with exceptions):
Example: If the efficiency rating of a 4-pole 7.5 kW motor is 86%, it belongs to efficiency class IE1. If the efficiency rating is 88.7% or better, the motor is assigned to class IE2. If the motor has an efficiency rating of 90.4% and 92.6%, the motor belongs to the IE3 and IE4 categories.
The IEC 60034-2-1 standard also provides a detailed definition of how the IE class of asynchronous motors is determined. For motors that are operated directly from the mains, the efficiency rating is based on the measurement point.
Regulation (EU) 2019/1781 on electric motors and speed controls, which entered into force on July 1, 2021, defines exactly when motors of a particular energy efficiency class must be used. According to this regulation, motors must achieve efficiency class IE2, IE3 or IE4, depending on their nominal output power and other properties. For example, three-phase motors with a nominal output power between 0.75 kW and a maximum of 1000 kW must have the efficiency level IE3 by July 2021. From July 2023, efficiency class IE4 will be mandatory for motors with an output between 75 kW and 200 kW.
To meet the energy efficiency requirements of IEC 60034-30-1, motor manufacturers have adapted their motor concepts and designs. To achieve the higher efficiency ratings, among other things, stators with a higher copper mass are used, iron cores with thinner silicon sheets and a higher silicon content are used, the air gaps are optimized, and more conductor material is used on the rotor. As a result of these changes, IE3 and IE4 motors have a higher inductance and lower copper losses, so the inrush and starting currents are higher than those of standard IE1 and IE2 motors.
Switchgear that is used together with IE3 and IE4 motors must be able to safely handle both the higher starting and inrush currents. Care should also be taken to ensure that motor starters and soft starters are approved for operation with energy-efficient motors. Eaton motor starters meet the current IEC/EN standards of the 60947-x series and will also meet future standards. They are tested with up to 15 times the inrush current. As soon as the starting currents for operating IE4 motors are within these limits, they are controlled by Eaton motor starters.
To achieve IE4 efficiency, permanent magnet and synchronous reluctance motors, which only work with variable frequency drives, are often used in addition to conventional three-phase asynchronous motors. In order to control highly efficient motors, variable frequency drives require specially adapted control algorithms. Yet even in the case of three-phase asynchronous motors, the ratio of resistive to inductive resistances changes in the higher energy efficiency class, which in turn also changes the current vectors. If the variable frequency drive is not suitable for operating IE4 motors, this may have various effects: In the worst case, the motor may not start at all, and even if it does, it may not operate properly – in other words, it will not work efficiently. All the variable frequency drives of Eaton’s PowerXL family are designed for operation with IE4 motors and can control standard induction motors, three-phase asynchronous motors, permanent magnet motors, brushless DC motors and synchronous reluctance motors, irrespective of the manufacturer.
In order to improve energy efficiency, plans are underway to increase the use of motors with a high energy efficiency class. However, it is important not to look at the motor in isolation, but in connection with all other components of the drive system and always within the context of the application. More detailed information about (EU) 2019/1781 is provided in the white paper “Successfully increasing energy efficiency in drive technology” by the energy management company Eaton, which is available for download on the company’s website.
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