1. How do I know if a motor is efficient?

Electric motors are rated in IE efficiency classes according to IEC 60034-30-1. The higher the number, the more efficient the motor. IE3 or IE4 are efficient motors. All the information on the efficiency classes of motors can be found under standards & regulations.

2. Can you save energy with a frequency converter?

A frequency converter on its own does not yet save any energy - to the contrary. It adds its own 3% to 5% losses. Savings of more than 40% can be achieved in closed systems (e.g. in ventilation systems or pump circuits) by reducing the motor speed and thus also the flow of air or water instead of using a throttle. Further information can be found in fact sheet no. 25: Frequency converter (so far only in german & french).

3. How do I know if my motor has saving capacity and how much this would be?

Topmotors has gained a large amount of practical experience from over 4 000 systems in diverse sectors in industry over the last 10 years. That is why the 4-step audit method Motor-Systems-Check was developed. It helps users to measure not only the motors, but the entire motor driven system including all the components (frequency converter, motor, transmission, application, etc.) and to estimate the potential energy savings. The Motor-Systems-Check helps you to identify the largest potential savings from a variety of motors. The free software tools facilitate the systematic analysis of the entire machine park.

4. What motors can I currently use in Switzerland or in Europe? What are the legal minimum requirements?

The current legislation and the applicable minimum requirements can be found in standards & regulations.

5. Are there ways to get funding for improving the efficiency?

Yes. The information and contacts for this topic can be found under financial incentive programs.

6. Where can I learn how to properly size and efficiently operate a motor driven system?

Topmotors offers a wide range of documents with valuable information free of charge under the section Knowledge. The fact sheets (so far only in german & french) provide you with comprehensive basic knowledge on specific technologies and topics. In addition, we regularly stage events, such as workshops on alternating topics or the Motor Summit where experts present the latest findings and the participants exchange data and ideas with each other. Topmotors is also organising webinars on alternating topics. Our 6-day advanced training course in Industrial Energy Optimisation (IEO) provides participants with intensive advanced training on efficient motor driven systems in industry.

7. What are harmonics?

Ripple harmonics or harmonic waves are often referred to as harmonics. They are caused by the frequency converter due to the pulse-width modulation and have a negative impact on the efficiency of the motor and the mains power supply. Further details and more in-depth information can be found in fact sheet no. 25: Frequency converter (so far only in german & french).

8. As a manufacturer, where can I find the relevant legal requirements for my product ?

The Ecodesign regulations for motors, circulators, water pumps and fans set out in detail the conditions under which a motor must meet the requirements. You can find all the details under standards & regulations.

9. My new motor needs more power than the old one. How can that be possible?

A "new" motor (e.g. IE3) has lower losses than an "old" motor (e.g. IE1). As a result, the motor also has a lower slip and therefore its speed is about 1% to 3% higher. If, for example, the old motor on a pump or a fan is replaced 1:1 by a more efficient one, the system runs faster and thereby unnecessarily discharges more air or water. This means it consumes more electric power. This additional consumption can be the same or even greater than the lower consumption due to the improved efficiency of the motor. Therefore, the new nominal speed must be adapted to the old speed. More information on this issue can be found in fact sheet no. 25: Frequency converter (so far only in german & french).

10. Should I put a frequency converter on my old and oversized motor?

Older motors (over 10 years) are not necessarily suitable for being supplied by a frequency converter. The switching sides of the voltage occurring in frequency converters can damage the insulation of the stator windings in a short space of time. The overspeed is limited due to the mechanical properties. Additional cooling might be required at lower speeds. Further information can be found in fact sheet no. 25: Frequency converter (so far only in german & french).

11. Is it true, that IE1 motors with short cycle times are more efficient than IE3 motors because they have a higher moment of inertia due to their greater mass?

According to Appendix 2.7 of the current Swiss energy efficiency ordinance about the energy efficiency requirements of series-produced installations, vehicles and equipment, in Switzerland only efficiency class IE3 (or IE2 with frequency converter) for motors between 0.75 and 375 kW with 2, 4 or 6 poles is authorised. IE1 are no longer eligible for sale.

What can be said is that more efficient motors are generally equipped with slightly heavier rotors. This gives you a higher moment of inertia and takes a little more time (fractions of a second) to get to full speed or to change rotational speed. This effect is not relevant for all normal operating modes (S1 and intermittently S2, S3, etc. according to IEC 60034-1) and only matters for FVD-driven servomotors that make rapid angle changes. However, these types of motors are exempted from the scope of the minimum legal requirements.

12. What should I keep in mind if I want to reduce network pressure in my compressed air network to save energy?

Reducing grid pressure by 1 bar results in an energy saving in the order of 10%. Whether or not a reduction is possible depends on many factors, such as type of consumer, required pressure, pneumatic grid and pressure losses, etc.

If the system is well planned, the consumers with the highest requirements (e.g. highest pressure) are close to the compressors and not at the end of a long pipeline network with high losses. The provided pressure of the compressors only needs to be as high as the application with the highest required pressure. So, the grid losses do not have to be added up to make sure that "enough arrives at the end". Otherwise, pressure throughout the grid would be this high only for a single application, with all other applications receiving unnecessarily high pressure.

Depending on how critical the process is, the minimum network pressure can be determined by trial and error. The pressure of the grid is reduced in weekly steps of 0.1 bar until it has some form of negative impact. If this happens, pressure is immediately increased by 0.2 bar, becoming the new grid pressure.

13. Do IE5 motors already exist?

The IEC 60034-30-1 standard for fixed-speed electric motors - motors designed for operation both direct on-line and with frequency converters (e.g. almost all asynchronous motors) - specifies efficiency classes IE1 to IE4 defined at 100 % rated power. In addition, this standard already specifies that there can be a next stage with motors in a new efficiency class IE5 that have 20% lower losses.

In the Technical Specification IEC TS 60034-30-2 technical specification for speed-controlled motors - i.e. electric motors that are operated exclusively with frequency converters (e.g. almost all permanent magnet motors) - the efficiency classes for IE1 to IE5 are defined at 90 % rated speed. A reduction in the efficiency of the motor is taken into account, because energy losses of the motor are 15 % - 20 % higher due to the converter supply with non-sinusoidal current. There are already speed-controlled motors on the market that reach the IE5 class of energy efficiency of the IEC 60034-30-2 standard.

More under standards & regulations.

14. Do frequency converters (FCs) have an influence on the service life of motors?

Frequency converters (FCs) can have an impact on the durability of motors - both positively and negatively. A lower power output of a motor due to a reduced speed leads to lower temperatures, reduces the mechanical load and thus wear. For the insulation of the windings in modern motors, FC operation is no problem today, even over a long period of time. However, it is important to ensure that the motors are designed for FC operation and that undesirable bearing currents are avoided, e.g. by using insulated bearings. Bearing currents damage the rolling bearings in the long run and increase wear.

You can find much more information on bearing currents in Basics No. 11 «Bearing currents» and in Fact Sheet No. 31 «Bearing currents» (Winter 2020). A webinar covering bearing currents is available in german: Topmotors Webinar No. 10: «Einfluss von Lagerströmen auf die Standfestigkeit von Motoren»

15. Do frequency converters also have an efficiency rating?

The frequency converters are classified according to their efficiency into three groups, IE0 (low energy efficiency), IE1 and IE2 (high energy efficiency). The efficiency classes for alternating current drives are defined in IEC 61800-9-2.

From 1st of July 2021, frequency converters for the operation of motors with a power output of 0.12 kW to 1000 kW must also meet the minimum energy efficiency requirements (at least efficiency class IE2). This ensures that the frequency converters are also efficient and contribute to a high degree of overall efficiency of the drive system.