DC motors for variable speed applications

03 October 2019 | Web Article Number: ME201916271

Motors, Drives & Transmissions
DC motors for variable speed applications

LEROY-Somer LSK direct current (DC) motors provide cost-effective solutions for variable speed applications.

That’s according to Grant Robertson, Managing Director of Vert Energy, exclusive distributors for Leroy-Somer in Southern Africa.

“Leroy-Somer has a depth of experience with AC and DC variable speed drive systems and designs its standard motors to withstand the new demands being imposed by frequency converters and variable speed operation.

“Motors are thus able to withstand frequent speed or torque changes and reversals, running at overspeed (up to 6 000 rpm for the standard four pole machine) and at lower speeds with full torque, without drawbacks like overheating, loosening of stator windings and damage to rotors or bearings.”

Robertson said the major advantage of direct current motors was the ease of effecting accurate speed control, adding that LSK's advanced technology enables motors to respond to electronic controllers which place great demands on the performance of DC motors.

“Smooth running has been achieved by the introduction of an advanced frame design, incorporating the largest dimensioned shaft.”

LSK square laminated frame DC motors, which have been designed by Leroy-Somer to the latest European standards for industrial requirements, have ratings from 2 to 750 kW. Leroy-Somer also produces non-standard motors, providing a range of power from 0,06 kW to 18,5 kW.

Vert Energy’s LSK DC range includes enclosed permanent magnet motors, enclosed wound motors, drip-proof wound motors and drip-proof, force-cooled wound motors.

These motors can be foot, flange or foot and flange mounted. Flanges are incorporated into the steel stator castings, giving a robust construction that eliminates vibrations. Four removable plates allow direct access to brushes for easy replacement, thus simplifying maintenance.

The design of the DC motor incorporates cooling and ventilation systems that reduce wear and tear on the brush gear, by the elimination of dirty particles.

These motors, with a Class H insulation system, can operate at ambient temperatures of between +5°C and +40°C and are protected with a range of surface treatments that withstand harsh environments. Robertson said the quality of the winding, insulation and impregnation guarantees optimum performance, even in arduous conditions.

Optional features include flange adapters which enable the easy modification of motors to all types of situations, without the need for costly and time-consuming adjustments. Pressure switches monitor air flow to detect if the ventilation motor has stopped working.

Where there is little vertical space for installing a motor, a connection kit can be used to mount the standard forced cooling unit in an axial position. Transparent doors can be fitted to facilitate maintenance procedures like brush inspection, without having to remove inspection doors.

The modular concept of this range enables a continuous production line for the entire LS product range, thus reducing delivery times. Lead times for adapted motors are also significantly shortened.

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