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Selection of motor for explosive atmosphere and drive

In selecting a motor with drive for explosive atmospheres, the motor manufacturer’s instructions and recommendations must be followed. Since only the motor can be installed in a potentially explosive atmosphere, with the drive always in a safe area, the instructions are intended to prevent the motor from overheating or creating any sparks. To ensure safe operation, certain issues need to be considered when selecting a motor together with a drive.

Requirements
Selection of motor and drive
Dimensioning
Insulation and filters
Thermal protection
Installation
The selection of motor and drive starts by collecting the customer requirements for ambient conditions, for the supply voltage and frequency, motor shaft speed area, motor output load, load type and overload requirement, efficiency requirements, and especially zone, gas/dust group, temperature class and Ex protection type required. So it starts with motor selection.
Check the availability of the motor and drive, the motor's certificate and whether the certificate is valid for the frequency converter operation and with what conditions.
When dimensioning a motor for variable speed applications, continuous thermal dimensioning and short-time overload capacity should be considered. Also limiting the switching frequency via Ex parameters will derate the amount of current and should be taken into account in the calculations. 

The most convenient method to dimension the motor is to utilize ABB’s DriveSize program. This tool can be downloaded from the ABB website (http://new.abb.com/drives/softwaretools/drivesize).

Dimensioning can also be performed for ABB converters using motor load capacity curves. The load capacity curves show the maximum permitted continuous output torque of the motor as a function of supply frequency. The output torque is given as a percentage of the motor’s nominal torque. The load capacity curves are based on nominal supply voltage.

Note! The maximum speed of the motor must not be exceeded. 

The load capacity curves are calculated for a certain switching frequency depending on the ABB converter type. Since the switching frequency is different for different converters and load types, to ensure safe operation, especially with non-ABB drives, the combination of motor and drive must be tested for the specific type of protection needed. The alternative is that the motor internal temperature sensors are connected to a certified PTC/Pt100 relay which controls the main contactor of the drive and disconnects the motor from the power supply if the temperature limit is exceeded.

Note! Any filters that are fitted must be taken into account when dimensioning the motor. 

Load capacity curves and more information can be found in the Low voltage Motors for explosive atmospheres catalog.

Other issues to consider
Short-time overload capacity, filters and insulation, ambient conditions, voltage drop in long cables.
Choose the insulation and filters according to voltage and frame size. Different motor manufactures have different instructions.
Depending on the motor protection type, different manufacturers take a different approach to fulfill the requirement of the standards. Check whether the combination has been type tested, and whether over temperature protection is required in the certificate. Choose the ATEX certified safety devices accordingly.
Follow the installation instructions provided by the motor manufacturer, especially the cable and EMC recommendations in accordance with local regulations. Configure the drive according to the motor rating plate and drive rating plate values. Check that the drive's switching frequency can be limited to the value required by the motor manufacturer. Additional safety can be achieved by commissioning the load capacity curve when available.