Food & beverage 29
Selecting motors and drives for explosive atmospheres W
hen selecting variable speed drives and motors for potentially explosive atmospheres,
the manufacturer’s instructions and recommendations must be followed, otherwise explosion protection
measures will be compromised. ABB’s Luciano Santos and Andrew Bould share some advice. Throughout the food and beverage sector, variable speed drives (VSDs) and electric motors are renowned for contributing to productivity improvement and energy efficiency. However, their use needs to be very carefully considered in applications within potentially explosive atmospheres.
It is for these reasons that correctly dimensioning a motor and VSD combination is critical, as getting this wrong can
atmosphere. These atmospheres have a defined zone classification which defines the minimum safety level (category) to which the
compromise explosion protection measures.
motors must comply. The category defines the permitted motor protection types.
The key is to follow the motor manufacturer’s instructions and recommendations. For instance, the instructions are intended to prevent the motor from overheating
Motors can be classified by equipment protection level (EPL) according to the IEC/ EN standards. The EPL indicates the motor’s
or creating any sparks. Meanwhile, the accompanying VSD must never be installed within a potentially explosive atmosphere and needs to be located away from the motor, in a safe area.
inherent risk of ignition. The purpose of this classification is to make it easier to select motors for different zones. For motors, the EPL marking is included in the Ex marking, and the equipment category is included in the CE marking.
Choosing a motor and drive Selecting a motor and drive combination starts by gathering the customer’s
Classification into categories is particularly important, because all the end user’s
Flour dust, for instance, is potentially explosive and in high enough concentrations, when combined with oxygen and an ignition source, such as a hot surface or a spark, it can combust.
requirements including ambient conditions, supply voltage and frequency, motor shaft speed area, motor output load, load type and overload requirement, efficiency requirements, as well as the zone, gas/dust
inspection, maintenance and repair duties will depend on the category of the product/ equipment, not on the zone where it is installed. The following highlights examples of Ex motor protection types and methods
In enclosed areas it can have devastating results. In fact, airborne flour dust is even more explosive than coal dust. Since it is not realistic to eliminate flour dust and oxygen from a typical bakery facility, ATEX regulations instead focus on removing ignition sources.
group, temperature class and Ex protection type. Armed with this information, the correct motor type can be selected.
given in the IEC/EN standard to ensure safe operation when a motor is fed from a VSD.
Motor protection types Motors are directly connected to the load or machine within the potentially explosive
Flameproof - Protection type Ex d When using protection type Ex d with an AC drive, the motor must be tested together with the drive for the duty intended and with the
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