The Zest WEG group, including its group companies, EnI Electrical and Shaw Controls, has success- fully completed an extensive contract, worth about R200-million, at Lubambe Copper Zambia’s Konkola North project, located near the town of Chililabombwe.

Lubambe is a 50:50 joint venture between African Rainbow Minerals and Brazilian mining giant Vale.
The scope of the Zest WEG group’s contract, awarded in 2011, covered the supply of all electrical and instrumentation elements for the expansion infrastructure and wet plant.

This included medium-voltage (MV) and low-voltage (LV) electric motors, MV variable-speed drives (VSDs), phase-shift transformers and all motor control centres (MCCs), both containerised and freestanding.

“There has recently been a swing towards the use of big squirrel-cage motors and VSDs for mill applications, compared with previous years, where slip-ring motors were exclu- sively used,” says Zest WEG group manager for automation Johan van Niekerk.

At the Konkola North project, the Zest WEG group supplied a 4.4 MW six-pole 3 300 V B3 WEG squirrel-cage motor and a WEG MVW01 VSD on the semiautogenous grinding (SAG) mill, with a three-winding VSD transformer manufactured at the WEG factory in Brazil.

“The WEG MVW01 VSD is particularly important in this application because of its high frequency, in excess of 90% efficiency, which is critical in large-kilowatt applications, where losses can be potentially high. These units are of a modular construction that make operation and maintenance relatively simple and makes it possible to customise control software,” he says.

WEG has developed a frozen-charge protection, specific to mill applications, where the torque and angular rotation of the mill are monitored, allowing for the detection of frozen charges in the mill. Should detection occur, the mill trips and alerts the operator before any damage can occur.

Further, the company and EnI Electrical were responsible for the installation of all electrical infrastructure from the main utility substation to the con- sumer substation and the MCCs, as well as for the supply of all electrical equipment, including cables, racking and instrument cables.

This work package included 11 kV overhead line reticulation in and around the plant, all lighting and small power, including six scissor high masts, electrical reticulation for all the ventilation shafts, five substations and the supply of all electrical cables and equipment for the underground portion of the project.

The Zest WEG group company Shaw Controls secured 15 MCCs for the project, adding to the company’s reference base on the African continent.

The ball mill has been supplied with a 6.2 MW six-pole 11 000 V B3 WEG slip-ring machine and the Zest WEG group team was given the rare responsibility of supplying all controls and auxiliaries around the ball mill package, such as an isolator on the VSD and its interconnections.

The Zest WEG group secured the supply of all the LV electric motors required for the project, including the mining portion and the process plant. In total, more than 500 units were supplied.