Apurpose manufactured 2 210 kW motor was successfully installed and commis- sioned by high-voltage electric motor repair company Marthinusen & Coutts (M&C) at the Katanga copper mine in the Democratic Republic of Congo.

“This is the third purpose-built motor manufactured by M&C for installation at this mine, the other two being 1 750 hp motors driving mills,” says M&C engineering director Henk de Swardt.

This is another installation where the company has designed and manufactured a fit-for-purpose electrical rotating machinery solution without the detail, which an original-equipment manufacturer would require, M&C states.

De Swardt explains that the company’s ability to purpose-build electric motors with minimal information and to engineer technological advancements into such machinery during manufacturing are significant strengths.

“One of our major challenges was coping with the lack of information about the load the [existing] motors drive. Both motors were estimated to be more than 40 years old and were made in Belgium. A major concern was not having information about the load these motors could drive,” he says.

He indicates that the mine considered replacement essential owing to high maintenance, frequent failures and associated repair costs. In addition, the interchange- ability of parts was a concern because of the age of the motors, as currently six of these original motors are installed.

“Technical personnel from M&C visited the mine in 2010 to undertake a full assessment of the installation and the machinery. The outcome was the design of a replacement motor, which took all the original operating parameters into account. High levels of robustness and longevity were also incorporated into the motor, owing to the remote location of the mine and the harshness of its operating conditions,” states De Swardt.

He further adds that the 2 210 kW motor is a slip ring induction motor, which is not normally used in a pump application.

“The original motor incorporated a brush lifting gear, which was a high-maintenance item and prone to failure. Improvements included the replacement of this lifting gear with constant force brushes.

“To allow this upgrade, the cooling circuit had to be modified from a water-cooled system to an open-air circuit owing to water quality issues on site. The open-air circuit offers greatly improved cooling, lower running temperatures and increased installation life. We used a Class H insulation system instead of the original Class B system to improve the long-term life of the stator and rotor windings,” De Swardt says.

He notes that the use of modern design software allowed the rotor and stator design to be optimised to improve efficiency and torque, thus enhancing machine performance.

“The full-load temperature rise of the stator was 55.47 ºC and the rotor was 71.76 ºC with full load efficiency at 96.3%. This reduces energy consumption costs and the total cost of ownership.

“The new design includes a change to the motor’s bearing arrangement. The original motor’s bearing configuration suffered from frequent failures and high running temperatures. The new design bearing configuration took into account the operational factors and testing after manufacture verified the design data,” De Swardt says.

He explains that extensive testing, including testing under full load to verify performance parameters, was undertaken with the customer present at M&C’s well-equipped facility in Johannesburg.

“The robust design of the motor also ensured that the vibration levels were well within specification. A vibration level of only 0.63 mm/s root mean square (RMS) was measured with the vibration level specified being 2.8 mm/s RMS. It was clear that reduced vibration had been achieved through the design,” De Swardt concludes.