By Michael Young, Pre Sales Engineer, Secure Power at Schneider Electric

Variable speed drives (VSDs) form an integral part of mines today; it is an energy optimised solution integrated into various mechanical components prevalent in today’s mining operations.

For example, VSDs offer significant energy savings when integrated in mines’ cooling systems, which is particularly beneficial in times when operators are under increasing pressure to optimise energy usage.

However, as with many other components, VSDs’ operational effectiveness also undergo tremendous strain when exposed to unplanned power outages such as loadshedding. This damage is further exacerbated by the quality of energy when the power does return. Often when grid power is restored it’s not a pure sine wave (unclean power), which damages equipment.

To prevent damage to VSDs and reduce downtime, double conversion online uninterruptible power supplies (UPSs) can be connected to the inlet power supply of the said VSD drives. A UPS will ensure that when the power outage occurs, the VSD will not experience loss of power. Also, a double conversion UPS can deliver a pure sine wave while mitigating potential damage to power-sensitive equipment.

How does a double conversion UPS protect a VSD from damage? It converts power twice through the following:

Power coming in from the main grid is in the form of an alternating current (AC) input which may contain voltage spikes, distortion, and other anomalies.

This AC power is converted into direct current (DC) whereby voltage spikes and distortions are removed with the use of the rectifier and the DC power leaving the rectifier is then fed to an inverter as well typically used to charge a set of batteries.

The DC is then “Inverted” back into AC that is tightly regulated by the UPS and thus all power leaving the UPS is clean as connected to power the VSD drive.

Even though there is an interruption in power during a load shedding incident, the DC link within the UPS is maintained by the battery and the output voltage is unaffected and continuous.

Here it’s important to understand that a UPS is a temporary power solution, providing energy until power from either the main grid or other energy resources such as generators is restored.

About Michael Young

Michael Young, Pr. Eng.

Michael Young is a trainer, coach and mechanical engineer in the HVAC industry. He graduated from the University of the Witwatersrand in the field of Mechanical Engineering (B.Sc Mech Eng) in 2008 and qualified as a Professional Engineer (Pr.Eng) in 2013. Michael is passionate about promoting knowledge and helping other young engineer grow within the industry through his training workshops and coaching sessions. Michael can be contacted on or 073 171 2311 for any questions or HVAC training needs.

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