Electricity + Control October 2018

CONTROL SYSTEMS + AUTOMATION

tariff increase of 12,06% compounded, and the 20% energy reduction, it can be said that the water transfer system upgrade was a good investment. Other benefits In addition to the energy reduction, the system ben- efitted from the more accurately controlled process variables through built-in features on the VSD such as longer ramp-up and ramp-down times. This had an impact on pipe friction losses during pipe filling times and a reduction on water hammering during periods where a system stop command would be given. Mechanical stresses were also reduced on the coupling between the motor and the pump, and fewer losses would be seen due to the extended ramp-up and ramp-down times programmed. Other savings are also realised through man hours reduced during the start-up process – as the automation of controls meant there was now no need to have personnel present. In the event of pow- er failures, the system can now also automatically start and run to its system required demands. Acknowledgements Picture credits: AngloGold Ashanti Further credits: Sydney Higgo, instrument techni- cian at AngloGold Ashanti. Andre Olivier, chief electrician at AngloGold Ashanti Marchant de Kooker, electrical/cic/systems engi- neer at AngloGold Ashanti. Christo Landman, electrical foreman at AngloGold Ashanti.

HMI installed by AngloGold Ashanti.

Results and conclusion Optimising results were done with the system requirements maintained. Variable required flow rates on demand were achieved with the system pressure remaining in the required limits as well. Over and above these improvements, there was a considerable energy saving achieved, as shown in the graph below, which reflects data from the energy logger at the pump station. The figures indicate an average energy reduction of 20% when compared with energy loggings before the upgrades were made – thus improving sub- stantially on the estimated 15% predicted in Zest WEG Group’s original report. Measuring the capital expenditure costs of R320 000 against the savings gained since implementa- tion in October 2014, the payback time amounted to just over a year. The savings for the first year amounted to R300 000, based on the tariff at the time of R0,69 per kWh. With the annual average

Author: Christo du Plessis is part of the Drives and Automation team at Zest WEG Group in Johannesburg.

kW hour loggings for the period October 2013 and 2014, and November 2013 and 2014.

Electricity + Control

OCTOBER 2018

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