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Siemens has modernised a gearless grinding mill drive at Newcrest’s Cadia Valley Operations, near Orange in New South Wales, Australia. This is the first time that a gearless grinding mill had been equipped with a Sinamics SL150 cycloconverter control. The modernisation concept developed by Siemens allowed for most of the existing electrical equipment to be retained, thus reducing downtimes during conversion to a minimum. A new diagnostics system and an access point for remote diagnostics ensure an immediate increase in operational reliability and availability of the plant.With eight mines worldwide, by market capitalisation Newcrest Mining is the 4th largest gold producer in the world and the largest in Australia. Its headquarters are in Melbourne. At the Cadia Valley Operations, Newcrest operates two underground mines and one open pit mine. Ore is processed to a heavily auriferous copper concentrate in a crushing, grinding and flotation circuit. This two-stage grinding circuit consists of a 40 ft SAG mill with a 20 MW Siemens gearless drive and two parallel 10 MW gear driven ball mills. Siemens has now fitted the SAG mill with a Sinamics SL 150 cycloconverter for closed-loop control as well as with a Sinamics DCM control module for the excitation circuit – the first time that both types of converter have been used in a gearless drive. The grinding mill control system was switched to Simatic S7 and the control system to Simatic PCS7. The modernisation also saw the installation of new air gap and speed sensors as well as an access interface for remote plant diagnostics. The ageing closed-loop control and PLC systems were replaced whilst keeping the motor, transformers and power section of the old frequency converter.Siemens was responsible for the hardware and software engineering, delivery as well as for supervising the installation and commissioning the drive. The work was carried out during a planned shutdown alongside other modernisation and expansion work. Newcrest Mining signed a comprehensive three-year service contract with Siemens in 2010 encompassing both the provision of replacement parts and on-call service, as well as diagnostics, breakdown service and preventative maintenance. With the new remote-access point the contract can now be supplemented with a remote diagnostics service.