New AC motors successfully replace 30-year-old favourites

Paul Boughton

Designing a new series of motors to replace an established range that has enjoyed global success for over 30 years can be daunting. Jon Severn finds out how SEW-Eurodrive rose to the challenge by embarking on a five-year, multi-million-euro project.

Being a market leader does not mean that a manufacturer automatically has the most technologically advanced products. For example, if a range of motors has been very successful and sales are still strong, there may be little incentive to 'reinvent the wheel' by developing a new range. Having manufactured the compact, versatile and reliable DT/DV series motors for over 30 years, SEW-Eurodrive found itself in this situation.

However, the company realised that the motors' capabilities were starting to lag behind customers' requirements, and there were concerns that the motors would not meet new standards and regulations relating to energy efficiency.

It was therefore decided that a major development programme was required to create what has recently been launched as the DR series AC motors. SEW-Eurodrive undertakes such major projects on core product ranges approximately once every decade. With the continual evolution of design technologies, these major projects do not follow a rigid formula but must adapt to suit the technological requirements of the products being developed and the design tools available at the time.

With a budget in double-digit millions of euros, the project started to build up momentum towards the end of 2002 with a series of national and international sales conferences, as well as an analysis of several market studies from organisations such as Frost & Sullivan. All of this helped the project team refine their aims and objectives. In particular, it became clear that the new motors must be easy 'drop-in' replacements in applications where the previous DT/DV series motors were being used, plus the new series needed to be a modular platform on which future developments could be based, especially with regard to efficiency standards and regulations. As an illustration of the ever-changing standards scene, the IEC has recently published IEC 60034-30, Efficiency classes of single-speed, three-phase, cage-induction motors (IE Code), as a Final Draft International Standard (FDIS), with formal publication expected in November 2008. It was only in April 2006 (after the DR series motor project had commenced) that Part 30 of IEC 60034 was first proposed. Despite the fact that the standard post-dates the DR series project, the motors already comply with the new standard.

Throughout the project extensive use was made of CAD, rapid prototyping technologies and specialised engineering tools developed in-house by SEW-Eurodrive. Although there was no product data management system, the project team used Microsoft Project to help manage the complex programme. Virtually all of the research and development work was undertaken by SEW-Eurodrive's own engineers, but Professor Hans-Jürgen Lannoch of FH Pforzheim, who has worked with SEW-Eurodrive on several previous assignments, provided input for the industrial product design. Numerous aspects of the DR series are now protected by either patents or registered designs, which highlights the high degree of innovation incorporated within the resulting modular motors

With a family of motors that is destined to replace well proven models, reliability is essential. Not only did the new units therefore undergo a full set of tests in compliance with the requirements of IEC 60034-1, Rotating electrical machines - Part 1: Rating and performance, but the enclosures, brakes, encoders and other components were also subjected to a rigorous testing regime in line with SEW-Eurodrive's own internal standards.

Design features

One of the key features for the DR series motors is that standard and energy-efficient models share the same design. The Standard Efficiency (IE1) four-pole AC motors are designated the DRS models and feature a die-cast aluminium or copper rotor cage (indeed, SEW-Eurodrive claims it was the first company to use die-cast copper technology for high-volume production of energy-efficient motors in 2002). The DRS motors are offered in size 71 and larger, with power ratings from 0.37-200 kW. High Efficiency (IE2) four-pole AC motors are designated the DRE models and also have a die-cast aluminium or copper rotor cage. These are available in size 80 and larger, with power ratings from 0.75-200 kW. Premium Efficiency (IE3) four-pole AC motors are designated the DRP models and again feature a die-cast aluminium or copper rotor cage. These are available in size 90 and larger, with power ratings from 0.75-160 kW.

For a standard IE1 motor of a given size and power rating, SEW-Eurodrive offers an alternative high-efficiency IE2 motor of the same power in one size larger; a premium-efficiency IE3 motor with the same power is two sizes larger. All models comply with worldwide standards and the forthcoming standard IEC 60034-30 (see above).

SEW-Eurodrive believes that, in the DR series motors, it is the first company to offer three alternative brake sizes for any given size of motor. The reason behind this is that inverter-operated and high-efficiency motors require smaller holding and braking torques, respectively. Whereas conventional motor brakes are often oversized for these applications, the DR series motors can, depending on the application requirements, be fitted with smaller brakes, thereby enabling customers to pay only for what they need. On motors size 90 and larger, the brake is mounted on a friction plate that merely has to be attached to the end shield. This means that the brake can be demounted and replaced by one of the same or different size without the need to open the motor casing.
Another innovation is that the automatic disengaging or lockable manual brake release can be mounted in any of four alternative positions - unlike traditional designs that have a fixed position for the brake release.

DR series motors and brake motors can be supplied with - or retrofitted with - one of three types of built-in encoder. Moreover, the encoder is mounted between the end shield and the fan (rather than on the B end), which means it adds nothing to the overall motor length and it is protected from physical damage (Fig. 2). Connections for the encoder are located conveniently inside the motor terminal box.

Geared motors

While some customers will purchase DR series motors as standalone units, others will purchase them in the form of geared motors, taking advantage of SEW-Eurodrive's extensive range of helical, parallel shaft helical, helical bevel, helical worm and Spiroplan right-angle gearboxes (Fig. 3).

Following the successful launch of the DR series motors, Gregor Dietz, the product manager for geared motors, describes how the inevitable technical challenges were met as the project progressed: "During a period of five years there were a few unexpected problems. However, we solved all of these by the core teams having 'your-fix' meetings every two weeks, and the sub-groups worked independently to solve their own problems."

Dietz also highlights two factors that he believes made a major contribution to the project's successful outcome: "First, 'top-down' support from the general management and, second, the way the project was structured with a small team of experts from each company department (R&D, production, sales, purchasing, management) who worked effectively with a project manager who readily accepted the contributions from those team members."

In conclusion, Dietz emphasises the advantages that the DR series motors brings SEW-Eurodrive and its customers: "We can deliver the DR-motor in each efficiency class required anywhere in the world, from the USA and Canada, to Brazil, Australia, New Zealand, China, Europe, and so on. Each unit is part of this modular DR motor series and not a new line with new features. Furthermore, customers can use the various features (brakes, encoders and connectors, for example) on motors of any efficiency class."

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