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MechChem Africa
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February 2017
S
uccessful completion of challenging
electrical rotating machinery refur-
bishment projects has long been the
hallmark of Marthinusen & Coutts, a
division of ACTOM. It is this reputation that
secured Marthinusen & Coutts the contract
to complete the reassembly and recommis-
sioningof avery largesynchronouscondenser
in the Democratic Republic of Congo (DRC).
The repair contract was awarded to
Marthinusen & Coutts early last year by an
international electricity equipment company
currently engaged in an upgrade project on
the hydroelectric power supply system for
the DRC’s power utility, Société Nationale
d’Électricité (SNEL).
Richard Botton, divisional chief executive
atMarthinusen&Coutts, says that this order
was placed on Marthinusen & Coutts by an
international OEM who is a global leader in
electrical engineering.
The synchronous condensers are critical
components of the dc/ac converter station in
Kolwezi in theDRC, which converts dc power
transmitted on a 1 700 km transmission line
Marthinusen & Coutts was awarded a repair contract at a dc/ac converter station
in the Democratic Republic of Congo: for the synchronous condensers, critical
components of a power station that feeds the energy-intensive Copperbelt in the
Katanga Province.
Rewind and refurbishment
of three gearless mill drive rotor poles
A recent project which showcased Marthi
nusen & Coutts’ capability was the rewind
andrefurbishmentofthreegearlessmilldrive
rotor poles for a platinummine in the North
West Province. The enormous 17.5 MW,
4 220 V, 2 531 A, 12 rpm, 5.8 Hz grinding
mill motors are 15 m in diameter, are driven
by cyclo-converters that supply the motors
with a variable frequency to control their
torque, and allow the speed to be controlled
for optimummetallurgical processing.
Rob Melaia, engineering and technical
executive at Marthinusen & Coutts, says
that these are among themost critical large
special high profile motors in the world.
There are only two OEMs worldwide that
manufacture these enormous machines,
which have an assembled mass of 1 000
tons each.
“The rotor poles were subjected to
overheatingdue toanoperational 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 withOEMcapabilities and backup
that led the customer to award the contract
to Marthinusen & Coutts instead of to the
international OEM. It is always critical for
operationstohavethislevelofsupportavail-
able, providing skilled technical assistance
with very quick response times,” he adds.
The removal of the poles required a two-
day shutdown during which Marthinusen
& Coutts assisted the mine maintenance
personnel. The poles were delivered to
Marthinusen & Coutts’ Cleveland facil-
ity where thorough investigative work was
undertaken on them. After the results were
known, the best method to improve and
partially rectify the surface insulation of
the remaining 60 poles, was investigated,”
adds David Motloung, design engineer at
Marthinusen & Coutts. A two-part epoxy
spray treatment and repeated insulation
resistance tests under extremely wet
coil conditions were used to achieve this.
Motloung says this was to simulate the
worst case conditions on site with the ul-
timate purpose of evaluating a method de-
vised by Marthinusen & Coutts to improve
the insulation of the remaining poles still
fitted to the machine.
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.
Test results confirmed that a thicker coil
insulation did not cause it to run at a higher
temperature due to the reduced heat trans-
fer, and there was a negligible impact from
the reduced copper cross sectional area.
q
Marthinusen & Coutts Lead Field Services
Technician, Wynand Willemse applies finishing
touches to one of the SNEL 70 MVA synchronous
condensers completely refurbished in the DRC.
Synchronous condenser
reassembly and recommissioning
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.
froma foundation stiffness point of view. “We
are employing the services of arguably the
top balancing specialist in South Africa who
will carry out the dynamic balancing on-site,”
Botton says.
Marthinusen & Coutts’ understanding
of local conditions in Africa, and specifically
the DRC, provides amajor advantage. Skilled
technical personnel from Marthinusen &
Coutts’ centre of excellence in Cleveland,
Johannesburg, were deployed to site and the
condenseriscurrentlybeingrecommissioned,
“overseenbyourcustomerandSNELofficials,”
Botton concludes.
q
from a converter at the Inga hydroelectric
power station on the Congo River in the
north. The power fromtheKolwezi converter
feeds the energy intensive Copperbelt in the
Katanga Province.
The synchronous condensers supply the
necessary reactive power, which cannot be
transmitted via the dc transmission line or
providedby the converter station. The inertia
of the rotating assembly of the condenser
provides the necessary energy to stabilise
the power system in the region, which aids
the overall stability of the grid.
The repair work undertaken on the 90 t
rotor of the 70 MVA condenser involved
conducting a thorough inspection of the ro-
tor forging and bare rotor by Marthinusen &
Coutts’ on-site repair team. Thiswas followed
by the refurbishment of thebearings and test-
ing andfitting newsalient poles that hadbeen
manufactured earlier by the international
company to replace the original salient poles.
Marthinusen & Coutts is also responsible
for the balancing of the rotor. The heavy rotor
runs at 750 rpm ina compromised installation