By Jari Korkiakangas, ABB

A new generation of high performance motors based on synchronous reluctance technology is now emerging. Jari Korkiakangas, from ABB takes a closer look.

The future of electric motors
We believe there will be diversion within the motor industry. Induction motors picked from catalogues will no longer be the single answer for all problems anymore. In an attempt to reach ever higher efficiencies, one needs to start thinking about what properties are really needed in which application(s) and then select the motor type to suit those exact needs.

The majority of industrialised countries have what is known as a Minimum Energy Performance Standard (MEPS) scheme. Europe has International Technical Commission (IEC) regulations with IE2 efficiency as the minimum level.

Australia was among the first countries to introduce MEPS1 in 2000 and MEPS2 in 2004. MEPS3 is expected in 2015. MEPS3 is still being worked on but we expect the most likely outcome to be that MEPS3 shall follow IEC and namely IE3 efficiency very closely. We predict that Australia will most likely extend the AUMEPS motor range. Currently the range is from 0.73kW to less than 185kW. With MEPS3, the range may be extended up to 375kW.

Meeting the ever-increasing efficiency requirements with conventional induction motor technology is a challenge. With current manufacturing technologies and most common materials, it is possible to meet IE3 and even IE4 levels with large motors of 75kW and up.

For smaller motors it is going to be a struggle to increase the efficiency in a cost effective way. This is noticed with the timelines for adopting IE3 for smaller motors, as an example – Europe has given two years extra adoption time to manufacturers.

Increasing induction motor efficiency can be done using more advanced materials. For example by implementing lower resistance dynamoplate plus copper in rotor cages and so on. All of these materials greatly impact the cost of the motor – at least in the short term, until manufacturing methods have been perfected and production volumes for better raw materials have increased.
Induction technology challenges have made motor manufacturers search for alternative, more cost effective, motor technologies for increasing overall efficiency.

Currently, there are two readily available technologies which can push motor efficiency up to premium IE4 or even way past that, to super premium efficiency.

To date, most common premium efficiency alternatives have been permanent magnet type motors. This is an excellent technology as long as it is able to overcome the challenges that have appeared over the last few years. Permanent magnet motors use neodymium magnets in the rotor. Neodymium is a relatively rare earth metal and its supplies’ are currently limited. Increased demand and limited supply has quadrupled the price of neodymium in just a few years. Mining projects are exploring new sources but it will take time to get the production to a level which meets the demand.

An alternative to the premium efficiency option is Synchronous Reluctance technology. ABB is the first motor vendor to embrace this technology across a wide range.

What is synchronous reluctance?
Synchronous Reluctance as a physical phenomena means that the magnets will always find the easiest possible way to travel between north and south pole fields. If a magnetic north and south pole field was created and an iron rod placed in between them, the flux would affect the iron rod and align it so that it creates a path between the poles. Like, for example, if you place a piece of metal in the vicinity of a horse shoe magnet – it snaps that metal piece between the poles thus completing the circuit. Flux travels through steel much easier than through air. That same principle works in synchronous reluctance motors.

In synchronous reluctance motors there are several poles – typically four. The rotor is built in a way that it creates several pathways for the flux to travel, allowing the air between the pathways to work as an insulator.

When the magnetic fields in stator are put to rotating movement, the rotor wants to follow the fields – because it is completing the magnet fields, and it naturally wants to stay in a position where it is easiest for the flux to jump across the air gap.

The image opposite demonstrates a cut out view of a synchronous reluctance motor’s rotor. One can quite easily notice the iron pathways provided enabling the flux to travel.
The greatest advantage of this technology compared to induction, is that the rotor is cageless and currentless because the rotor is not magnetised but it instead is part of the magnetic field.
With induction motors a current is induced to the rotors squirrel cage. Induced current magnetises the rotor, allowing it to follow the magnetic field of the stator. Since there is current in the rotor there is then also resistance. Resistance turns electricity into heat aka losses, instead of rotating motion.

Since the synchronous reluctance rotor is currentless it means that there are no rotor losses. This can equate to reduction losses of up to 40% compared to induction motors.
Another valuable feature of this technology – besides greatly improved efficiency – is the redistribution of heat sources in the motor. In an induction motor the rotor is typically the hottest part. From the rotor, heat emanates through the shaft to the bearings. The hotter the bearing, the shorter the grease life – which amounts to frequent service and maintenance issues. Since the synchronous motor’s rotor is lossless it runs cool. A cool rotor means a cool shaft and cool bearings. The majority of the heat generated in synchronous reluctance motors is borne in the stator.

Further research and development – integrated packages
New technologies such as permanent magnet and synchronous reluctance motors still have their challenges. One of the challenges is that both of these motors cannot be operated directly from the network. Both of them require a variable speed drive to start them.

Add a variable speed drive to the system bumps up the initial capital cost but in the majority of cases the cost of the additional drive is paid back in a very short time frame – particularly if the application is such that it can benefit from added speed control.

Synchronous reluctance technology usage
Synchronous reluctance motors can be used in multiple applications. As a variable speed drive is always needed to accompany these applications, then the best applications are those where it is natural to adjust process performance i.e. the speed of the motor. Most commonly these would be pumps and fans. The industrial sector has a plethora of pumps and fans. They can be found amongst city infrastructure – in buidlings, in local municipal water pumping stations, at mine sites, cement mills, throughout general manufacturing, plus at food and beverage processing facilities – to name a few.

Electric motors in industry are using almost 30% of all electricity available. The large bulk of the motors are running pumps and fans.

Our studies further show that 90% of the motors are running constantly at full speed and the process output is being adjusted by throttling or other mechanical means. An extreme comparison would be to think about how you drive a car – certainly you don’t drive around flat out, adjusting the speed with the break pedal while maintaining the gas pedal to the floor. That wouldn’t be very efficient, nor safe.

At ABB we believe that there are many more processes around Australia that would benefit from adding variable speed drive to control process output. While making this transition, we believe it is beneficial to opt for premium efficiency motors such as synchronous reluctance to ensure greater energy efficiency.

Find Motors, Drives And Engines Related Companies In The Pump Industry Capability Guide

Related articles

©2024 Pump Industry. All rights reserved


We're not around right now. But you can send us an email and we'll get back to you, asap.


Log in with your credentials


Forgot your details?

Create Account