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Motor selection considerations

17 August 2020

Keith Gale offers advice on some the main considerations when selecting an electric motor for use in food processing applications. 

A ‘must get right’ component in the food manufacturing process – to ensure smooth and continuous efficient production – is the electric motor. When selecting a motor for a specific task there are many considerations, from power supply through to regulation compliance. If the motor is a replacement unit and it is being changed frequently it may not be right for the application. 

When evaluating a motor’s performance in an existing function, there will often be scope for system improvements or a need for upgrading to meet changing efficiency legislation requirements, BSI and EN specific industrial standards, or new even more demanding cleaning regimes in the current climate.

Essential factors to consider include power, output, speed, available space, power to size and weight ratio, mounting, duty cycles, starts per hour, working environment, ingress protection (IP rating), level of cleaning or sterilisation and compliance.

If the motor is a replacement, and is IE2 or lower, you should consider installing an IE3 alternative (IE3 0.75 to 1000Kw, IE2 minimum 0.12<0.75Kw). This would conform with regulations that will be introduced in July 2021, as well as being a far ‘greener’ solution. You might even consider IE4 or IE5 to benefit from further energy savings.

In wet environments and locations that need to be washed down frequently, motors can fail due to moisture ingress through inadequate sealing if the required IP rating is not considered. IP66/IP69K stainless steel motors are approved for high-pressure hose washdowns and cleaning-in-place (CIP) which helps to avoid machine downtime. These smooth bodied motors eradicate the entrapment areas found on standard motor cooling fins. With no flaky paint or rust, they offer a good option for hygienic applications.

Asynchronous AC induction motors are the main workhorses employed for machinery on production lines, providing cost effective power, while servomotors are typically used where precise motor control is essential to give accurate speed and positioning. The most up to date Permanent Magnet Synchronous Motors (PMSM) can offer advantages, especially where continuous running is involved. They offer greater energy efficiency (up to IE5) helping to reduce running costs. An inherent benefit of this technology is that motors are significantly smaller, in some cases half the size and weight of their induction motor equivalent. In addition, the IE5 permanent magnet motors offer ‘future proofing’ with regards to meeting all energy efficiency legislation. 

Complementary products to adapt or modify motor performance include gearboxes, brakes, inverters and feedback systems such as encoders. Gearboxes can be used to achieve increased torque and reduce output speed. Principally there are two forms of braking function, parking and dynamic. Braking can be achieved either mechanically or electronically via an inverter with DC injection braking, although in many applications the failsafe benefits of electro-mechanical brakes are preferred. These brakes can also be split into AC and DC, high and low torque to match the application.

Inverters provide motor control and contribute to achieving a more efficient operation, both in functionality (such as speed control) and energy saving. These variable speed drives are available in IP20, IP55 and even IP66 for the more demanding food, beverage and pharmaceutical environments.

After evaluating with an Enhanced Product Approach (EPA) – considering the complete system requirements – you might feel there is a combination of potential enhancements that would benefit your operation. In which case, a package solution that brings together these elements could ensure a happier marriage of the components involved.

Keith Gale is a motor specialist at Lafert Electric Motors.

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