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ROUND UP

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

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

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

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

DRIVES, MOTORS + SWITCHGEAR

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.

Electricity+Control

January ‘17

16