Electrical switching & drive systems & components


Electronic variable speed drive systems

March 2011 Electrical switching & drive systems & components

Through the recent acquisition of Velo Control, BMG Drives has extended its product portfolio to include Danfoss variable speed drive systems.

The Danfoss range, which encompasses dedicated pump controllers, provides efficient pump performance in applications where a certain pressure or level needs to be maintained over a wide dynamic range. Danfoss pump cascade controllers, with features and functions that eliminate the need for PLCs and other external controllers, increase the efficiency of multiple pump or blower systems. These dedicated controllers ensure accurate flow, pressure and level control. This results in a lower energy consumption compared to valve throttling or the conventional across the line on/off cycling of pumps and blowers.

Cascade controllers allow staging of up to four additional drives and/or fixed speed motors. Using the master drive’s PID controller, the system provides precise control in large pumping systems. Other important features include minimal wear on driven equipment, enhanced energy savings and optimum productivity in diverse sectors.

Lead pump alternation functionality distributes running time equally across all connected pumps, ensuring optimum efficiency of the system. Wear on individual pumps is minimised and the service life of each pump is extended.

These cascade controllers also operate pumps of unequal size and are available with master/slave cascade control. The master drive controls the speed and staging on or off of the additional adjustable speed slave drives.

Running a large pump at variable speed over a wide dynamic range is not an ideal solution because of low pump efficiency. Also there is a practical limit of approximately 25% rated full load speed for running a pump. In the basic cascade control, the drive controls a variable speed motor as the lead motor and can stage up to two additional constant speed motors on and off. By varying the speed of the initial motor, variable speed control of the entire system is provided. This maintains constant pressure, eliminating pressure surges and resulting in reduced system stress and quieter operation in pumping systems. The basic cascade controller can control up to three equal size pumps, with lead pump alternation to equalise pump run time and wear. This has application in pressure booster stations, where fixed speed pumps are started and stopped as required, while the speed controlled pump or fan is utilised to match the exact flow demand, keeping the system pressure constant.

The extended pump cascade controller is available with three additional relays and the advanced controller has the option of eight additional relays.

For more information contact Dave Dyce, BMG, +27 (0)11 620 1530, [email protected], www.bmgworld.net



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