Searching for cost efficient efficiency

European Ecodesign standards are pushing for higher efficiency machines and processes through more efficient use of electricity. That pushes the need for higher efficiency products used in those machines and processes. Two of those products, variable speed drives and motors, are the focus of the new Ecodesign EN50598-2 standard. This standard introduces International Efficiency, or IE classes for drives, and an International Efficiency of Systems (IES) classification for the drive and the motor together. 

In addition, EU legislation Regulation (EC) No 640/2009 requires that new IE2 motors (from 7.5 to 375 kW) sold after January 1, 2015 be used with a variable speed drives (VSD). And the newly released EN 50598-2 standard sets the groundwork for future regulations focused on motor and drive efficiencies (together), and eventually the complete driven system (motor, drive and pump, for example).

Facing higher efficiency demands from customers, Kolmeks, a Finnish pump manufacturer, looked for higher efficiency motor and drive solutions. As product manager Jori Suokorte explains “The Ecodesign directives keep up to the limit, the minimum level needed in the field. Sometimes consultants want us to select products that are even better than the minimum requirements, regarding legislation.”

Looking at the options

Regulations and standards notwithstanding, understanding the options for higher efficiency motor and drives is a good first step. Variable speed drives, by design, are typically very energy efficient. There are losses in any drive, but when compared to the energy savings versus running motors direct-on-line, these losses are easily offset.

That leaves the motor. Motor efficiencies focus on mitigating heat losses. These losses typically come from the rotor. Reducing those losses saves energy. Currently, there are three mainstream motor efficiency options.

Adding active materials

Increasing induction motor efficiency is typically achieved by adding more active (usually copper) materials to the stator windings. The induction technology and motor construction are the same, so no changes are needed with the familiar maintenance schedules/workshops. Rotor current losses will still be present, and the resulting heat transferred to the motor casing and bearings. Motor bearing failures are the primary cause of induction motor malfunctions. Additionally, the added copper in the stator may increase the frame size and will increase motor weight, both considerations for machine builders.
Increasing induction motor efficiency typically requires adding more active materials. This increases the weight and size of the motor.

Use permanent magnets

The second option is to use permanent magnet motors. Rare earth permanent magnets are designed into the motor’s rotor, eliminating the need for a magnetizing current. Because of this, there is no rotor current and therefore very little heat being transferred to the rest of the motor and bearings. This immediately improves motor energy efficiency. However unlike induction motors, permanent magnet motors require the use of a variable speed drive to control the motor. The drives continuously change the stator magnetic field resulting in rotation. The rare earth magnets are subject to market conditions, setting a variability in their price. Additionally, maintenance becomes more challenging. Certified service workshops who are capable of working with the strong magnetic forces while ensuring the magnets are not damaged when dismantling the motor are required. During planned maintenance this may result more time that the motor is not available for the process. It’s important to consider these costs across the lifetime of the motor.

Something in-between

Synchronous reluctance (SynRM) motors are a third option. SynRM motors take advantage of the proven simplicity and reliability of induction motors and the higher efficiency of permanent magnet motors, but without the use of rare earth magnets. It’s the motor’s rotor design that makes this possible. Using the stator of an induction motor, the rotor is replaced with a specially designed rotor that aligns with the stator’s magnetic field. Like permanent magnet motors, SynRM motors also require the use of a variable speed drive to control the motor. The drive calculates the offset angle of the magnetic field, resulting in rotation. Looking at lifetime costs, SynRM motors are maintained the same as induction motors, no certified workshops are needed because there are no rare earth magnets. No rare earth magnets take the variability out of the motor purchase price. With no need for a rotor magnetizing current, the rotor runs cooler and that means less heat is transferred to the motor and bearings. 

ABB’s SynRM rotor design aligns with the stator's magnetic field, the drive calculates an offset angle to rotate the shaft.

What does this mean for Ecodesign standards?

The new EN 50598-2 standard defines the IE classification for complete drive modules (CDM), which is the variable speed drive and any auxiliary equipment connected to the drive (like a brake chopper, EMC filter, etc). It also defines a Power Drive System (PDS) International Efficiency of Systems, or IES classification, which is the combination of the motor and CDM. It’s important to note that the CDM IE classification is determined at 90% frequency and 100% total current. This is different from motors, where the motor IE classification is determined at 100% motor speed and 100% motor torque. It’s not possible to add a CDM IE class and a motor IE class together to get an IES classification.

To get the IES classification, both the motor and the CDM need to be taken together for measurements or calculations. These are done by the manufacturer of the drives or motors. Here the standard defines that if a manufacturer only produces the drive or the motor (not both), the manufacturer should use a motor reference model or a CDM reference model (as defined in EN 50598-2). For manufacturers that produce both the drives and the motors, that manufacturer can determine the IES without using reference models.

How does the IES classification help?

Additionally, for both the CDM and the IES classifications, there are eight operating points defined where efficiency values are provided. These values can be used to help calculate total efficiencies of a machine at different operating points, help calculate payback times, and even help estimate potential energy savings and CO2 reductions. The points even can help with dimensioning a system.

Pumps are a great practical example of this. Pumps typically run in a best efficiency area, at partial loads. If a pump manufacturer needs to provide efficiency information for the complete pump systems (motor, drive and pump), the pump manufacturer will look to the drive and motor manufacturers for the IE and IES information. If the products come from the same manufacturer, that manufacturer could provide the IES directly.

ABB is the first manufacture to provide verified package efficiency values according to EN 50598-2 for their IE4 SynRM motor and drive packages. In addition to the eight points defined in the standard, we also provide eight additional points, for a total of 16. The partial load values in these statements helped Kolmeks make their decision to go with the ABB solution. As Jori Suokorte explains “One thing that I have noticed in SynRM motors is the partial load is available in very high efficiency, and that is what we, pump people, are interested in because many times, nearly always, the partial load efficiency is even more important than the maximum load efficiency.” And he continues “This is because, when you are using a drive for speed control, the pumps are running with low power, and when you have good efficiency in that position, it gives you a very low lifecycle cost.” According to Suokorte “The high efficiency is number one reason we selected SynRM motors, because nowadays, all the customers require high efficiency and low life cycle costs. That’s the first and number one reason we are interested in SynRM motors.” 

Finnish pump manufacturer Kolmeks now offers pumps with ABB's IE4 SynRM motor and drive package to meet ever increasing customer energy efficiency requirements.

Not just for pumps

The savings potential available from ABB’s SynRM packages are not only limited to pump and fan applications, they are also great solutions for compressors and all types of industrial uses, especially constant torque applications.

One constant torque application is extrusion. Manufacturers are looking for ways to save energy without having to make design changes to existing machines. In Nottinghamshire, UK, Synseal Extrusions replaced a 20 year old extruder servo motor with an ABB SynRM motor and drive package. In this constant torque application, the upgrade cut 20 percent off the running costs of the extruder, a savings of about $1,200 per year, from just the one machine. The same benefits are available for other continuous processes, such as wire drawing machines.

SynRM motor and drive packages are used in both constant torque (like extrusion) as well as quadratic torque applications like pumps, fans and compressors.

Understanding the options

Today’s higher efficiency motor and drive give machine builders many choices. Finding the solution that provides the efficiency needed while keeping lifetime costs low benefits both the machine builder and their customers. The emerging EU Ecodesign standards and regulations will continue to push for higher efficiency, and at ABB, we’ll continue to provide solutions that work for you today and in the future. 

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