Electricity + Control January 2017

ROUND UP

DRIVES, MOTORS + SWITCHGEAR

Excellence in refurbishment of critical electrical rotating machinery

A recent project undertaken by Marthinus- en & Coutts , a division of ACTOM, was the rewind and refurbishment of three gearless mill drive rotor poles for a platinum mine in the NorthWest Province.The enormous 17,5 MW 4 220 V 2 531 A 12 r/min 5,8 Hz grinding mill motors, that are 15 metres in diameter, are driven by cycloconverters which supply the motors with a variable

frequency to control their torque and also allow the speed to be controlled for opti- mum metallurgical processing. Rob Melaia, engineering and technical executive at Marthinusen & Coutts, said: “The rotor poles were subjected to over- heating due to an operational error, and we were approached by the mine to assist,” Melaia says. “While this contract could be seen as a simple procedure, we believe it is the immediate access to a large local service provider with OEM capabilities and back-up that led the customer to award the contract toMarthinusen & Coutts instead of to the international OEM.” The removal of the poles required a two day shutdown during which time Marthinusen & Coutts assisted the mine maintenance personnel with this task.The poles were delivered to Marthinusen & Coutts’ Cleveland facility where thorough investigative work was undertaken on the defective poles to determine the extent of the damage caused by the overheating.

“The second part of this activity was to investigate the best method to improve and partially rectify the surface insulation of the remaining poles of which there are 60 in total,” adds David Motloung, design engineer at Marthinusen & Coutts. Marthinusen & Coutts made use of a two part epoxy spray treatment and repeated insulation resistance tests under extremely wet coil conditions. David Motloung said that this was to simulate the worst case conditions on site with the ultimate purpose of evaluating a method devised by Marthinusen & Coutts to improve the insulation of the remaining poles still fitted to the machine. “This solu- tion can be implemented in-situ negating the need to remove the poles to improve the insulation,” he explains. Motloung says that after studying the design of the pole coil it was decided to use a different conductor for the rewind as this would increase the insulation integrity.

Enquiries: Richard Botton. Tel. +27 (0) 11 607 1700 or email richardb@mandc.co.za

Marthinusen & Coutts' rotating machines design engineer, David Motloung, records photographic evidence of tests on one of the enormous gearless mill drive rotor poles recently refurbished by the company.

Local company powers Mozambican graphite mine

The remote operation to mine one of the world’s largest finds of high grade graphite – the Balama deposit in Mozambique – will be powered by a generator plant being constructed through South Africa-based Zest Energy, part of the ZestWEG Group . According toAlastair Gerrard, managing director of Zest Energy, the plant will begin producing electricity during the first quarter of 2017, with an initial capacity of 12,5 MW from an installation of seven 2 200 kW diesel generators. “The isolated location of the Balama mine – over 250 kmwest of Pemba in northern Mozambique – means that while the operation

various companies within the ZestWEG Group, locally and world- wide.The containerised power generators includeWEG alternators with automatic voltage regulation systems, as well as motorised louvres, generator auxiliary systems, and fuel and lube tanks. To cool the engines, a horizontal-type radiator system, rated for 50°C ambient temperature, was manufactured in South Africa and each radiator includes 10 WEG 3 W fan motors positioned in two cooling banks of five fans each. Enquiries: Kirsten Larkan.Tel. +27 (0) 11 723 6000 or email marketing@zestweg.com

does have access to power from the national grid this will need to be supplemented to ensure an adequate supply for full plant demand,” Ger- rard says. “We are therefore required by the customer to ensure 100% availability, and have consequently designed the plant with substantial standby capacity to allow for maintenance and repairs without affecting the continuous supply.” He says the plant, which was the largest foot- print project yet tackled by Zest Energy, would initially run with seven 2 200 kW generators; six running and one on standby, and would later be expanded to include eleven generators, of which two will be standby units. Equipment for the ex- tensive scope of supply has been sourced from

Electricity+Control January ‘17

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