System integrator MCS Control Systems, which undertakes regular energy and productivity reviews for Weetabix, initially invited variable speed drive partner Sentridge Controls to conduct an energy appraisal.
While looking at applications from vacuum packing to air compressors, it examined the extruders, which account for up to 30% of the site's energy consumption.
Portable energy loggers were installed to the incoming supply to monitor kW, kVA, kVAr, power factor, current and voltage.
As a result, eight ABB industrial drives, five ABB general purpose drives and low-voltage ABB motors, rated from 0.75—250kW were installed during a two week phase, part of which was the plant's shutdown period.
Following the installation, further measurements were taken and a 20% drop in energy consumption observed – meaning a £28,000 annual saving from installing ac drives.
However, from an engineering perspective, Weetabix says it has also eliminated maintenance on the drive train, with no carbon brushes to replace, no forced cooling, and no feedback devices – since the gearboxes are protected by the torque limit control on the ac drive.
That will save another £20,000 per year.
"The new ac drive technology brings greater torque control and speed accuracy, thanks primarily to ... direct torque control," says Dave Chapman, MCS Control Systems' site engineer.
"Unlike dc drive technology, which needed a tachometer feedback arrangement to maintain accuracy, using DTC, no encoder feedback is needed," he explains.
"That reduces complexity and cost; yet we are able to get a far better control of the process resulting in a constant extrusion rate."
Allan Norman, manufacturing manager at Weetabix's extruder line, adds: "Dc drive technology is subject to surging, which affects the product output.
"Because the speed and torque control are now so accurate, the rotating knife that cuts the extruded wheat, can do so in a more uniform manner.
"This means that the cooking time of the end-product is optimised; there is minimal temperature fluctuation which further saves energy."
But Norman also says a key factor in Weetabix's choice of drive and motor controls is "the engineering skills of the people" involved.
"MCS Control Systems and its drive partner have excellent engineers, that know what they are looking for and offer sound and timely advice," asserts Norman.
"This probably accounts for the fact that, following installation, we started the extruders on Sunday evening and they ran without a hitch until turned off on Friday night."