MACHINE BUILDING & FRAMEWORKS FEATURE
HOW TO SLOW over-speeding fans
Fans don’t normally need a braking resistor and chopper but when they are operating in a closed system, a situation may arise where one fan will over-speed the next and the DC bus voltage on their motor drives will then rise. Here John Mitchell, business development manager of CP Automation, reports on the case of GA Pet Food Partners in Leyland, Lancashire
E
xternal dynamic braking choppers are useful to drive manufacturers, panel
builders and end users alike. A seventh IGBT (isolated-gate bipolar transistor) for the chopper in a six-pulse drive is one way drive manufacturers can reduce the cost of
Right: GA Pet Food Partners operates an environmental extraction system comprised of three parallel 185kW ABB motors
These units allow for a fit and forget procedure. During emergency stops the unit will still function because it is powered by the DC bus and not by an external supply. These were key features for a fan application at GA Pet Food Partners. GA Pet Food Partners works with some of the biggest global pet food businesses. However, it doesn’t manufacture an own label product because it doesn’t believe in having an own brand. It sees itself as a partner, not a competitor, to its customers. GA Pet Food Partners operates an
the product by rating the IGBT to a given torque and duty level. Some six-pulse off the shelf AC drives manufactured today have a seventh IGBT built-in as standard. The calculation for sizing the internal brake chopper is not a difficult one, but getting accurate data in the first place can be. Some brake choppers on board a drive range from 25-100% ratings, and let’s not forget the fact that not all drive manufacturers fit a seventh IGBT above ratings of 22kW.
ENTER THE EXTERNAL BRAKE CHOPPER
To this end, CP Automation offer a range of external brake choppers that cover 99% of application needs up to 360kW peak, 100kW continuous. Available in nine models across three
frame sizes, there are several options to set the threshold to the desired switching level, along with fault output and master slave options to chop higher power levels.
/AUTOMATION
Above and right: the new GA Pet Food Partners factory is home to a very technically advanced extrusion plant
environmental extraction system comprised of three parallel 185kW ABB motors spinning the Halifax fans cascading into smaller fans, and was encountering difficulty in decelerating the biggest of these units. The effect of over-speeding becomes cumulative the more fans there are in close proximity on a factory floor. The three large fans are controlled by Allen
Bradley Powerflex 753 variable speed drives (VSDs) from Rockwell Automation, which count among their features, predictive
diagnostics to extend the life of cooling fans. Jayne Whittaker of GA Pet Food Partners
explained, “In an environmental extraction system, if a fan runs too fast, it either pressurises air too much at one end or creates suction at the other. Some machines on the shop floor have exhaust fans, which need to run at the appropriate speed. CP Automation supplied external brake resistors and retro-fitted brake choppers within the existing panels that house the Allen Bradley drives.”
ADVANCED EXTRUSION
The new GA Pet Food Partners factory is home to a very technically advanced extrusion plant, making some of the finest dry pet foods. GA Pet Food Partners has invested in the world’s first thermal twin extruder, which allows it to include high levels of fresh meat in premium dry pet foods without the use of dry meat meals. With four extruders, the company has a production capacity of 100,000 tonnes of super premium pet food and can make batches from 3-200 tonnes to suit small or large brands, delivering the same quality and consistency whatever the batch size. CP Automation has also supplied braking resistors for Control Techniques drives on an extruder and a hammer mill. “Our focus is on helping the customer achieve the best possible result, by integrating technology from a range of global partners that we have spent years creating,” explained CP Automation’s John Mitchell. “We aren’t that unlike GA Pet Food
Partners in some ways. Just as they choose not to operate an own label, so they can work more effectively on behalf of their customers, much of our work is in the background. We are a layer behind the machine itself at component level. It’s here that we are able help make the manufacturing process more efficient, more cost effective and more sustainable - in every sense.”
CP Automation
www.cpaltd.net T: 01724 851 515
Enter 208 AUTOMATION | MARCH 2014 21
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