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Efficiency measures should be built into the complete drive system says Nord

18 October 2011

It is Nord Drivesystems' view that energy saving does not stop at optimising the consumption of individual motors but that practical efficiency measures and a 'green' approach should also be built into the complete drive system together with consideration for the overall application process. Nord has developed innovative efficiency optimised drive features that include high-frequency operation, automatic flux adjustment, energy recovery, and intermediate circuit coupling.

An example of this is the option of operating asynchronous motors with an output frequency which is higher than that of the mains in order to increase efficiency. Motors with 230V/400V star-delta circuitry can be operated at up to 87Hz with a 400V inverter in a delta connection, whereby the motor can be operated at a higher speed of up to 87Hz with the rated torque. Up to 100 Hz approximately, this increase in frequency results in an improvement in the efficiency of the motor by up to 5%.
Intelligent control is another way to save energy. For asynchronous motors, frequency inverters generally maintain the magnetic flux level required for yielding the full torque over the whole speed range, thus causing unnecessary losses during partial load operation. Nord’s SK 200E, SK 500E, and SK 700E- frequency inverters can save resources by automatically reducing magnetisation when the motor is operated under partial load for potential energy savings of up to 30%.

Whilst conventional frequency inverter applications discharge the braking energy as heat, more efficient and eco-friendly drives reuse this excess energy via intermediate circuits and regenerative braking, thus reducing mains power. The efficiency of a system can be increased even further, where all the drives are linked to form a DC network, the generated energy is supplied directly to other drive units. The energy not used by the network may also be fed back to the mains via a regeneration unit.

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