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 refi ning. 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 benefi ts 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 effi ciency 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

Vacon Drives UK Ltd.

18 Maizefi eld,

Hinckley Fields Industrial Estate Hinckley

Leicestershire, LE10 1YF, UK

Tel. +44 (0)1455 611 515

Fax. +44 (0)1455 611 517

E-mail: vacon.uk@vacon.com

Web: http://www.vacon.co.uk RS

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other drives we had tested. And there was another important

benefi t – the Vacon drives was very competitively priced!”

Since selecting the Vacon AFE drives as the preferred op-

tion for its batch centrifugals, Broadbent has discovered that

they offer another signifi cant 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.

With conventional regenerative drives, loss of supply while

the centrifugal is braking frequently leads to failure of the

main fuses in the drive system. Not only is this a major incon-

venience, the fuses are also special semiconductor protec-

tion types that are expensive to replace. With the Vacon AFE

drives, however, this problem does not occur.

“We’ve now been using Vacon AFE drives for around fi ve years

and as well as offering consistently excellent performance,

they’ve also proved to be exceptionally reliable,” said Graham

Hindle. “We now fi t them to our batch centrifugals unless, of

course, the end user expresses a preference for drives from

an alternative manufacturer.”

Very good support

“We get very good support from Vacon, with prompt deliver-

ies and easy access to expert technical advice and guidance

although, in truth, we have rarely needed this. I suspect that

Vacon’s repair service is just as good, but the reliability of the

drives is such that we really haven’t had enough experience

of it to comment!”

For Thomas Broadbent & Sons, Vacon AFE drives are provid-

ing major benefi ts and these same benefi ts can be enjoyed in

many other applications. In fact, wherever dependable cost-

effective drives that support regeneration and generate low

levels of harmonics are required, the Vacon AFE units are an

ideal choice.