For some time Queensland Magnesia’s (QMAG) Rockhampton plant had been experiencing poor electricity supply conditions in the form of frequent voltage fluctuations.
Even a 2-second voltage dip would cause their air blowers, which are critical in the operation of the plant’s gas-fired shaft kilns, to trip. If one of these blowers were to stop, the whole plant would shut down.
“On certain types of power dips we were getting the kilns tripping and the kilns, if they trip like that, it can put them out of action for a few days sometimes—just from a very momentary dip in voltage,” explains QMAG’s Electrical Engineer, Don Wilschefski.
An eight-hour restart procedure could follow, resulting in a considerable loss of production.
“It would happen whenever we had a dip. It had been happening ever since the plant was built—probably a couple of times a month. And you’ve got the potential to lose a day or two’s production if things aren’t going too well,” says Don.
So QMAG decided to install new and replace existing variable speed drives on the shaft kiln air supply lines. When the plant management approached Schneider Electric’s Drives and Motor Control Sales Engineer, Gary Clews, he quickly grasped the main issue and offered a solution.
“We had to change those drives anyway as some were quite old—14 or 15 years old, the drives on the blowers—so we really had to upgrade them and we were just looking at the best option to do that and the Altivar drives seemed to look pretty good,” says Don Wilschefski.
“They were new technology and we spoke to Gary about the ride-through characteristics and he assured us we could set them to have a good ride-through characteristic on voltage dips.”
They chose Schneider Electric’s Telemecanique Altivar 61 (ATV 61), which are designed especially for pump and fan applications. Choosing from the wide range available—from 0.75 to 800 kW—QMAG had a 160 kW and a 250 kW ATV 61 drives installed on each line: one drive for each stage.
“We managed to get them in and set all the parameters correct and they seem to be running quite well now,” says Don.
“We’ve had quite a number of dips without causing any trips on the kilns that we’re running.”
One of the other advantages of the ATV 61 drives was their compact size.
“With retrofitting in any organisation, you’re normally trying to fit things into spaces that don’t exist,” explains Don.
“It wasn’t quite the case here, but with the drives we removed and putting the new ones in, it has created a bit of extra space for us.”
However, it was mainly their ride-through ability that sold them. The voltage dip ride-through feature of both the Altivar 61 and 71 range allows the user’s machinery to continue operating without tripping during supply dips and ‘brown-outs’ on one, two or all three phases.
“The ‘ride-through’ time depends on several things. It works best on high inertia loads. It also depends on how many phases brown out and how low the voltage drops,” explains Gary Clews.
“In the case of QMAG, they get brown-outs that cause the lights to go out for two to three seconds, but the drives do not even slow down. For periods longer than that the drives begin to slow down gradually, but have never tripped. In the past, a two-second brown-out would cause the plant to shut down,” Gary says.
“Reliable and robust, the Altivar range assures continuous service. It withstands voltage drops of up to 50% without drop in output— its large DC bus capacitors which store the electric charge and release it as required during the supply dip—and handles a polluted or dusty environment and temperatures up to 50°C” explains Vinod Kandoi, Product Manager of Variable Speed Drives and Soft Starters.
Since the installation of the ATV 61 units Schneider Electric has trained QMAG staff in servicing of the drives and the company has purchased several small drives, ranging from 15 to 55 kW, to replace old units throughout the plant.
“Schneider Electric had a representative visited us and gave us a good run down on servicing the drives—how to maintain them, how to change parts and that sort of thing. We also had a lot of telephone support when were initially setting the drives up,” says Don.
“We had some of the first drives in the country—I think we’d installed a couple before they were officially released—and some of the questions we had, they had to refer back to Europe to get the advice. But most of that time was on a construction phase, so we didn’t have a lot of down time with that.”
The staff at QMAG now feel confident that support is close at hand if things go wrong.
“We have purchased some spares and the closest technician is a two or three hour flight away which, with drives like that, is about as good as you’d get in Australia,” says Don.
“We haven’t really had any major issues with them at this stage.”
There are plans for more upgrades throughout the plant, including two Altivar 61 315 kW for air induced draft fans to the shaft kilns and six Altivar 71 250 kW drives to replace old DC drive systems on the briquetter roller presses. In addition to this, there are over 40 drives on the QMAG site, ranging from 11 to 75 kW, which will be replaced a few at a time during each scheduled shutdown.
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