29 November 2012 – The Zest WEG group has commissioned a range of equipment at Boteti Mining’s AK06 opencast diamond mining project in Botswana in execution of a contract awarded by EPCM contractor DRA. The electrical equipment was supplied in the form of a group package solution and was completed six weeks ahead of schedule on this fast-track diamond mining project located near the Orapa and Letlhakane mines.

“The integrated solutions we provided were custom designed for the project and our teams were closely involved in the application engineering process with DRA,” Zest WEG group’s David Claassen says.

The contract included the supply of a medium voltage (MV) mill package comprising a 4.0 MW 3.3 kV squirrel cage machine complete with phase shift transformer and 12 pulse MVW01 variable speed drive (VSD). Claassen comments that one of the main benefits of this application is the 99% efficiency on the VSD achieved by using high voltage IGBTs. The VSD technology is also very reliable and uses long life components.  In addition, the user-friendly VSD technology allows for programming and operation by staff with normal electrical qualifications. Specialised knowledge is not a prerequisite. WEG also designed the system for ease of maintenance, since plant downtime is critical. A key design factor is the power arms which are easily removed and replaceable within five minutes.

The greater contract included supply of nine miniature substations incorporating Lucy Ring Main Units (RMUs), which are solely distributed by the Zest WEG group. The mini-subs range from 200 to 1250 kVA, with voltages of 11 kV/550/420 VAC. Four fully extensible Lucy RMUs were also supplied as stand-alone outdoor units. The Lucy Sabre range comes standard in an IP54 configuration and is a very robust unit suitable for mining applications and outdoor use.

“Mini-subs have not been a part of our traditional scope of supply, but they were suitable in this application, owing to their synergy with the Lucy RMUs, the interchangeability of spare parts between the RMUs and the commonality of relays and programmes,” Claassen says.

The Zest WEG group also supplied all low voltage (LV) electric motors and VSDs. All free-standing VSD panels were application designed, built, tested and commissioned by the Zest WEG group, which also undertook and guaranteed the heating and ventilation calculations critical for the long term operational requirements. The LV motors were the latest generation three phase W22 IE2 units, which conform to the efficiency specification IEC 600343-30. As standard, these motors are IE2, IP66 with Class H installation. As with the MV drives, interfacing of the LV VSD’s was achieved using DeviceNet.

In addition, a standby power generator plant was supplied to AK06, including two 650 kVA containerised generators with full synchronisation to the mains designed by Zest WEG group company, IMS Cape. This was a non-standard and complex application whereby the generators were synchronised with two separate incomers and a bus coupler. This entire control system was designed and implemented by IMS Cape.