Feature Drives & Controls
key feature of the operations of the Omagh Minerals goldmine is a ball mill - essentially a large drum into which the ore is placed along with heavy balls. As the drum rotates, the balls gradually crush the ore into a powder from which the gold can be more readily extracted. Fully loaded, the ball mill at the Omagh Minerals site weighs over 50 tonnes, and it has been calculated that the torque required to start it is in excess of 24,000Nm. This mill is driven by a 250kW
motor, via a 5.8:1 ratio gearbox. However, problems had been experi- enced in the form of gearbox failures and as a result, Omagh Minerals called in bearing specialist Hayley Group to investigate. The conclusion was that the type of gearbox currently being used was only just adequate for the application, and that fitting a larger gearbox would improve reliability.
Gear box failure
Shortly after this conclusion had been reached, the in-service gearbox failed, putting the ball mill out of action. This was an issue in itself, however the best delivery available on the larger gearbox recommended as a replacement was eight weeks and Omagh Minerals was understandably reluctant to have the mill out of service for such a long period. Experts from the Hayley Group knew that the maximum load on the gearbox occurred when the mill was started and that, if this load could be reduced, a smaller gearbox, which was available on a much shorter delivery, could be used.
The key to reducing the starting load was to replace the direct online starter currently in use with a variable speed drive that would give a smooth con- trolled start-up with greatly reduced peak torque. However, this solution was only attractive if a suitable variable speed drive system could be obtained quickly. This is where Ralspeed came in, confirming that it could design, build and supply a panel for this application in just one week.
Service in a hurry
“The Ralspeed guys were as good as their word,” said Mark Jones of Hayley Group. “Because Ralspeed had designed specifically for the applica-
Electrical Engineering NOVEMBER 2011
A gold rush for VSD installation A
After a gearbox failure had stopped production at Omagh Minerals site in Cavanacaw, Ireland’s only operational goldmine, Ralspeed supplied a 250kW variable speed drive (VSD) system that allowed normal operations at the mine to be quickly resumed
great demands on the mechanical components in the drive chain,” said Jones, “but, as we’ve seen, these demands have been significantly reduced by the Ralspeed variable speed drive system. This gives us com- plete control over the rate of accelera- tion and deceleration of the ball mill drum, thereby eliminating shock loads on the drive system.
tion, it was quick and easy to install and commission, which meant that we were able to get it into service without delay.” With the replacement gearbox installed (albeit of a smaller size than that originally envisaged), and the Ralspeed variable speed drive system fitted in place of the original direct online starter, the ball mill was back in operation in less than two weeks. It has now been working reliably for sev- eral months without any sign of dis- tress to the gearbox or other parts of the drive system.
“This is an application that places
“This has turned out to be an effec- tive and convenient solution, not least because of the very fast delivery and excellent support provided by Ralspeed. We are confident that the new arrangement will make the ball mill much more reliable in future and, by eliminating costly breakdowns, it will pay for itself very quickly. In fact, I would have no hesitation in saying that, with this application, Ralspeed has certainly hit the gold standard for Omagh Minerals!”
Ralspeed
www.ralspeed.com T: 01254 582 345
Left: Ralspeed supplied a 250kW variable speed drive system at the Omagh Minerals site in Cavanacaw
Enter 214 VSDs supplied to MRC lab
Laboratory of Molecular Biology building currently being built on the Biomedical Campus in Cambridge. Effective and dependable air conditioning is a key
V
requirement for this new building, which is scheduled for completion in 2012 and which replaces the existing labo- ratory that, after almost 50 years of operation, has reached the end of its useful working life. To ensure the air condi- tioning installation is both readily controllable and energy efficient, Vacon 100 HVAC drives, which are specifically optimised for building services applications, have been selected for motor control. The drives used in this project range in size from 2.2kW to 55kW and all have been supplied in IP54 ver- sions so that they can be mounted directly on the walls of the building without the need for further protection. Integral BACNet/IP interfaces mean that the drives can
acon has supplied 67 drives from the Vacon 100 HVAC range to the new Medical Research Council
be integrated with the overall building management sys- tem (BMS) in the new laboratory, without the need for potentially costly additional components. The interfaces support full bi-directional communication with the drives, allowing their operation to be monitored and controlled by the BMS to ensure that the energy efficiency of the HVAC installation is optimised under all conditions. In addition to their integral network interfaces and their availability in IP54 versions, other key features of the Vacon 100 HVAC drives that made them particularly suitable for this application include space saving com- pact construction, fast set-up and interference-free operation which is guaranteed by built-in RFI and har- monic filters. The drives also use a high switching fre- quency to ensure that their operation is inaudible even in quiet environments. Long reliable service life with minimal maintenance
requirements is enabled by the use of conservatively rated components and, in particular, by the elimination of elec- trolytic capacitors. The film capacitors used in the Vacon 100 HVAC drives are not only inherently more reliable and less susceptible to ageing, they are also far more environ- mentally friendly when they are finally disposed of at the end of the life of the equipment. Vacon
www.vacon.com T: 01455 611 515
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