Drives: All things considered
14 Jul 2010
Energy efficiency should not merely focus on optimising the consumption of individual electric motors, but should encompass drive systems as a whole. And the provision of user-specific, customised, energy-saving concepts can ensure maximum cost efficiency and eco-friendliness.
Drives expert NORD takes such an holistic approach and employs a wide range of technologies, including regenerative braking, automatic magnetisation adjustment, copper rotors, 87Hz operation and intermediate circuit coupling.
Drives that reuse excess energy via intermediate circuits or regenerative braking provide a more efficient and eco-friendly solution. While a regenerative braking unit can feed other components elsewhere in a larger installation, energy generated and retained in a DC intermediate circuit can be consumed by the connected components directly without loss. In effect, less power is drawn from the mains.
Intelligent control is another way to save. Operating with asynchronous motors, frequency inverters generally maintain the level of magnetisation required for yielding the full torque over the whole speed range, thus causing unnecessary loss during partial load operation. The latest frequency inverters, however, can save resources by automatically reducing magnetisation when the motor is operated under partial load.
Users can thus save up to 30 % energy. Furthermore, compared with grid-powered constant-speed units, inverter-operated asynchronous motors can be run at higher output frequencies in order to increase efficiency.
Lenze’s new BlueGreen campaign takes a similar holistic approach to energy saving with electric drives, taking a three-pronged approach to evaluate the potential and maximise the possible energy savings. It encompasses energy-saving software for partial loads and the re-use of braking energy, which can often yield energy savings in a range from 20-50%.
A key BlueGreen strategy is to work with machine builders to use as little energy as possible, especially by ensuring drives are not oversized. Here the approach is for Lenze engineers to properly evaluate the requirement, using a specialist software tool for complex cases, and dimension the drive so that it runs fully loaded at optimum efficiency.
Where the demand on the motor varies, the answer is to use frequency inverters to match the demand. This can give a swift win, with 50% energy savings if the speed is only reduced by 20%; so payback times are short, and maintenance requirements reduced. A second strategy is to convert electric energy with a high degree of efficiency. A starting point is to use high efficiency motors: the change to using them is gathering momentum with legislation requiring a minimum of IE2 high efficiency by June 2011. IE2 motors are now available, including a wide range of IE2 geared motors with in-line or right angle gearboxes. In some cases dimensions change from IE1 standard efficiency motors, but all relevant electrical characteristics can be adjusted.
