broadbent spins energy savings with vacon drives Reference Story Thomas Broadbent & Sons, the UK’s preeminent developer and supplier of solid-liquid separation equipment, is now using Vacon AC variable speed drives with Active Front End (AFE) technology to recover up to 90% of the energy con- sumed by the batch centrifugals it supplies to the sugar pro- cessing industry. The centrifugals are designed for processing massecuite, a mixture of sugar crystals and molasses, which is produced by the crystallisation phase of sugar refining. The centrifugals spin the massecuite in a perforated basket, which typically has a diameter between 1.2 m and 1.8 m, at speeds of up to 1,200 rpm. The liquid molasses is forced through the perfora- tions, leaving behind sugar crystals that are ready to be sent to a granulator for drying. The batch centrifugals produced by Broadbent work with loads of between 1.5 and 2 tonnes, and can process up to 25 loads per hour. The centrifugals are driven by AC motors rat- ed between 160 and 400 kW, depending on the capacity of the machine. Because the operating duty is so onerous, standard motors are not ideal for this application, so Broadbent pro- duces special motors of its own design. Fitted with a non-regenerative drive, the centrifugals would have a very high-energy consumption and, in addition, during braking they would produce a lot of energy that would have to be dissipated as heat. For this reason, Broadbent adopted regenerative drives for its machines as soon as these became readily available. These drives allow the energy produced during braking to be fed back into the supply system, which means that the net energy consumption of the centrifugals is reduced by 80% or more. The problem of heat dissipation is also eliminated. The Broadbent engineers, however, constantly evaluate new technologies as they become available to determine whether they might offer benefits to the users of the company’s ma- chines. As part of this process, they investigated the use of Active Front End (AFE) drives. These are regenerative drives of a special type that incorporate controllable solid-state switches in their input section. “AFE drives provide high efficiency when operating in both motoring and regenerative modes, and they also generate a much lower level of harmonics than conventional regenera- tive drives,” said Graham Hindle, Chief Electrical Engineer of Thomas Broadbent & Sons. “We have, however, found that not all drives of this type work well with our higher torque mo- tors.” Dependable and cost-effective Vacon Active Font-End drives meeting customer needs “We were, therefore, happy to accept when Vacon offered to supply us with one of its AFE drives for evaluation. Our tests showed that the Vacon drive could readily be tuned to meet our needs and also that it offered better performance than