Electricity and Control July 2023

DRIVES, MOTORS + SWITCHGEAR

VSDs can help industry deal with loadshedding From mines and process plants to factories and workshops – almost every industrial enterprise in South Africa relies on electric motors – and electric motors are seriously affected by loadshedding. Zest WEG’s Pieter de Villiers here highlights how variable speed drives can be used to bridge the gap between grid electricity supply and backup power during loadshedding.

Pieter de Villiers, Gqeberha Branch Manager for Zest WEG.

V ariable speed drives (VSDs) are generally consid ered as essential contributors to energy efficiency, but they also have features that can reduce the op erational disruptions caused by loadshedding. De Villiers, currently Gqeberha Branch Manager for Zest WEG – and formerly the VSD Service Manager at the com pany – says, “Any industrial operation that relies on electric motors will face severe challenges to continuous workflow when loadshedding strikes. Much of the disruption is re lated to the process of starting up machinery again after a power loss. The startup often entails a series of sequential actions that an operator must oversee and implement.” De Villiers notes that many motor users are not aware of the usefulness of WEG VSDs in automating and controlling the startup procedure. WEG VSDs can be programmed to initiate a sequence of actions, so that this does not have to be done manually by the operator. A simple example to illustrate this would be where water is being pumped through pipelines and drains out during loadshedding. In most cases, the pumps cannot simply be started up again at full speed in a ‘dry’ condition without the risk of cavitation and other damage. “In cases like this, the WEG VSD can be programmed to start the pump at a lower speed until the pipeline is again full of water, after which it could resume full pumping du ties,” de Villiers explains. “Similarly, in a mining operation, for safety reasons, it is important for a siren to be sounded before a conveyor system is re-activated after the start of loadshedding. Here, the WEG VSD can be programmed to automate the re-start process, and it initiates the siren to warn staff that the conveyor will start running again.” He highlights that the full range of WEG VSDs have built in PLC capability, which allows for them to be programmed

WEG variable speed drives with built-in PLC capability can be used to restart motor-driven processes smoothly. in this way; there is no need for PLCs to be added to the system. Another function of VSDs that makes them valuable as sets in times of loadshedding is that they can serve to pre vent equipment from tripping out. This can happen when there is too much ‘dead time’ between grid power turning off and a backup generator kicking in. “If the dead time lasts more than a few seconds, many motor-driven applications can trip out and then require a re start, which can be time consuming and labour intensive. A common way that the VSD stays live during this dead time is through the stored energy in its capacitors, allowing it to re-accelerate the motor when the generator kicks in,” he explains. “It is also possible to set up the drive to use 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.” WEG VSDs also play a useful role when energy users want to harness renewable energy sources like solar pow er. In a hybrid power system where a motor is connected to both the grid and to a solar panel system, a VSD can use the best source to feed the motor. If there is sufficient sunlight, the system will detect the power flowing in from the panels and optimise that power source. “On the other hand, the VSD will switch to grid power at night or when it is cloudy,” says de Villiers. “This allows for motors to be kept running – and at the same time reduces the energy costs as well as the user’s carbon footprint.” □

These WEG variable speed drives can prevent equipment from tripping out during loadshedding.

For more information visit: www.zestweg.com

14 Electricity + Control JULY 2023