Modern Mining June 2023

“This is where VSDs are very useful, as they can be programmed to auto mate and control a number of actions in a required order,” he says. He cites a simple example of pumping water through pipelines, from which the water drains out due to gravity during load shedding. Starting the pump dry at full speed could create a vortex that causes cavitation and other damage. The WEG VSD can be set to start the pump at a lower speed to refill the pipeline with water, after which it could resume full pumping duties. He highlights that it is therefore not necessary to install a separate PLC sys tem to accomplish this level of automation. “This functionality can be extended to more complex applications, such as a mine’s conveyor sys tem,” he explains. “For safety reasons, a siren must first be sounded before the conveyor is allowed to be activated; WEG VSDs can be programmed to do this with the siren connected to one of the drive’s outputs and importantly no extra hardware would be required to achieve this function.” Load shedding often creates extra work for mines, as an operator must go through several stages to ini tialise a system. WEG VSDs can be programmed to automate this re-start, taking the load off operators and allowing them to focus on their key duties. Overcoming dead time The ‘dead time’ between grid power turning off and the mine’s generator kicking in also creates chal lenges for operational continuity – and is another area in which VSDs can come to the rescue. If the dead time is too long, then machines can trip out and require a re-start that is often time consuming. “A common way that the VSD stays live during this dead time is through the stored energy in its capaci tors, allowing it to re-accelerate the motor when the generator kicks in,” he says. “It is also possible to set up the drive to utilise the inertia from the load and therefore power from the motor itself – essentially using the motor briefly as a generator to keep the VSD alive.” As the world moves towards harnessing renew able energy, as many mines are doing, VSDs also have a role in enabling hybrid power systems. When a motor is connected both to solar panels and to the national grid, a VSD can provide the interface that can switch to the optimal power supply, he explains. “When there is sufficient sunlight, the system will detect the voltage produced from the solar pan els and use it instead of grid power, which in turn improves cost savings,” he says. “At night, or even in cloudy conditions, the drive can energise a con tactor to connect back to the grid – so this assists not only with load shedding but with overall energy efficiency.”

A range of WEG Variable Speed Drives that can prevent equipment from tripping out during load shedding.

A range of WEG Variable Speed Drives that have built-in PLC capability.

De Villiers notes that the full range of WEG VSDs have built-in PLC capability, and they can be pro grammed to suit the mine’s requirements. WEG has also developed certain programmes for its VSDs to help users accomplish a variety of common automa tion and control functions, without having to write or learn how to write this code themselves. 

The Zest WEG demo trailer displaying a wide range of WEG electric motors and the WEG CFW11 drive that can reduce the operational disruptions caused by load shedding.

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June 2023  MODERN MINING  33