10 May 2011
The centrifugals are designed for processing massecuite, a mixture of sugar crystals and molasses, produced by the crystallisation phase of sugar refining. The batch centrifugals 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 rated between 160 and 400 kW, depending on the capacity of the machine. Because the operating duty is so onerous, standard motors are not suitable for this application, so the company has always produced special motors of its own design.Fitted with a non-regenerative drive, the centrifugals would have a very high-energy consumption and, during braking, produced 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 they 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 can be reduced by 80% or more. The problem of heat dissipation is also eliminated.The Broadbent engineers constantly evaluate new technologies as they become available, including 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 regenerative drives,” said Graham Hindle, chief electrical engineer at Thomas Broadbent & Sons. “We have, however, found that not all drives of this type work well with our higher torque motors.“We were happy to accept Vacon’s offer to supply us with one of its AFE drives for evaluation. Our tests showed that the drive could be tuned to meet our needs and also that it offered better performance than other drives we had tested. There was another important benefit – the drives was very competitively priced!”Since selecting the Vacon AFE drives, Broadbent has discovered that they offer another advantage. They are well suited for use in applications where unpredictable interruptions to the supply are likely to occur, which is a common problem in some of the overseas locations where sugar cane is grown and processed.
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