New Danfoss Cascade Pump Controllers (Jan 2011)
“The Danfoss range, which encompasses dedicated pump controllers known for advanced technology and reliable operation, are used to provide efficient pump performance in applications where a certain pressure or level needs to be maintained over a wide dynamic range,” says Dave Dyce, electronics technical manager, BMG – Bearing Man Group. “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, which results in a lower energy consumption than 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, this 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 - often in water/wastewater applications - 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 and because there is a practical limit of approximately 25% rated full load speed for running a pump.
Various Cascade control options are available in the Danfoss VLT® HVAC drive system – a basic pump Cascade controller and embedded in drive software (standard, using 2 control board relays).
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 while eliminating pressure surges, 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.
As an example, in pressure booster stations, 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.
BMG Drives provides a national sales, training, repair, maintenance and spare parts service for the Danfoss range of electronic variable speed drive systems.