ABB delivers precise process control and ATEX compliance

Posted on 28 Jan 2015 by Jonny Williamson

The challenge of matching low voltage AC motors and AC drives for use in hazardous environments within the chemical, oil and gas industries has been overcome by ABB’s ATEX-approved motor-drive package.

ABB's ATEX-compliant motor-drive package
ABB’s ATEX-compliant motor-drive package.

According to ABB, few manufacturers make both motors and variable-speed drives making the search for combinations that are ATEX approved a growing concern to the industry.

The specialist in power and automation technologies gave the example of an end-user that chooses to match their own drive and motor combinations being forced to select a larger motor than optimum because of the limited selections available from their chosen manufacturers.

“If loadability curves are not available, then the ATEX137 work place directive will have to be implemented through a “self-assessment” route, which can be costly and time consuming.”

When controlling motors in potentially explosive atmospheres, ABB noted that is important to be aware of the effects an AC drive has on the operating conditions of a motor, compared to direct-on-line (DOL) operation. These can include higher voltage stresses through steep voltage pulses, common mode voltages and currents, and higher motor surface temperature rises due to a non-sinusoidal supply.

For these reasons, it continued, ATEX directives call for extra attention to be given when an Ex motor is used with an AC drive. Usually only the motor and driven load are installed in the potentially explosive atmosphere, with the drive being installed in a safe area.

ABB’s new ATEX package optimises an end-users motor and drive combination for their application, with surface temperature limits having been tested and verified at an ABB laboratory rather than on-site with a customer’s own test equipment.

Among the many sources of risk affecting AC drives and motors in hazardous environments is an increase in motor surface temperature. Reduced cooling capacity can be caused by driving the motor outside its specified speed range. Increased surface temperature can occur if the motor is incorrectly dimensioned for use with an AC drive.

When using an ABB industrial drive, its motor control platform – direct torque control (DTC) – can help reduce the temperature. Using DTC control, along with ABB’s dimensioning and selection tool DriveSize, can help prevent over temperature.

As well as ensuring surface temperatures are tested and controlled, ABB also offers ATEX-certified safe torque-off (STO) circuits and thermistor protection systems, able to disconnect the drive from the source of energy if surface temperatures are exceeded when the load is stalled or damaged.