Stator Winding Installation Completed on Two Massive Gearless Mill Drive Motors in Northern Zambia
Marthinusen & Coutts (M&C), a division of ACTOM (Pty) Ltd, has successfully completed the stator winding installation on two massive gearless mill drive (GMD) motors at a mining operation in northern Zambia. The project was completed in record time, demonstrating M&C’s expertise in large-scale electrical and mechanical engineering services.
The project involved the installation and connection of the stator windings, including the SAG (semi-autogenous grinding) and ball mill motors, 4 × 2 eight-quadrant joints and associated coils.
The SAG mill is among the largest in Africa, measuring 12.5 metres in diameter and 6.5 metres in length, with an installed power rating of 18 MW. It is designed to process approximately 2,450 tonnes of material per hour, equivalent to around 20 million tonnes per annum.
Among Africa’s Largest Electric Motors
The scale of the two gearless mill drive motors presented significant engineering and logistical challenges.
The ball mill is driven by a 16,000 kW, 64-pole, 4,000-volt motor with 480 slots, while the SAG mill is powered by an 18,000 kW, 88-pole, 4,000-volt motor with 648 slots. The motors are among the largest electric motors of their type installed in Africa.
Due to their enormous size, the motors are transported to site in quartered sections and assembled using some of the largest mobile cranes available. Each quadrant weighs approximately 65 tonnes, while the complete motor assembly measures approximately 20 × 3 metres, with a stator internal diameter of 12.6 metres.
Specialist Stator Winding Installation
Each joint incorporates seven large, uninsulated overhang “flexible” coils designed to accommodate pitch requirements. The remaining coils are standard resin-rich, diamond-type coils, with each coil weighing approximately 44 kg.
Because the mill drives operate in an exposed environment, protecting the windings from weather, moisture and contamination was a critical consideration throughout the installation. Special precautions were implemented to prevent moisture and dirt from entering the winding system, while custom-designed equipment and tooling were used to support the various installation activities.
Led by Richard Botton, M&C CEO, the project team comprised between 10 and 14 specialists who performed a range of technical functions and installation tasks. The team worked to stringent quality requirements, with comprehensive quality-control measures implemented throughout every stage of the project.
Rigorous Testing and Quality Control
M&C conducted detailed inspections and operational checks following the installation to verify the performance and integrity of the mill drive systems.
As part of the comprehensive testing programme, the team monitored key parameters including electrical currents, temperatures and mechanical responses. These checks helped ensure that the motors were operating correctly and that the installation complied with the required industry standards.
Record-Breaking Project Completion
The scale and complexity of the installation required specialist expertise, meticulous planning and efficient execution. Despite these challenges, M&C completed the SAG mill motor installation in just 31 days, while the ball mill motor installation was completed in 28 days.
The successful completion of the project within these record timeframes once again demonstrates M&C’s capability to deliver specialised on-site engineering services for some of the largest and most technically demanding electrical machines in the mining industry.
Through its combination of specialist skills, experienced personnel, purpose-designed tooling and rigorous quality-control processes, M&C helped ensure that the mill drives were commissioned and brought into operation in the shortest possible time.
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