3782 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
sea level (masl), creating additional challenges such as the
thermal behavior, voltage distances, transport to site, and
all site services.
Compared to the largest GMD in operation nowadays
– 40 ft, 28MW – building GMDs up to 44 ft, 35 MW for
SAG mills and 32ft, 30MW for ball mills represent up to
30% motor torque increase (which is the main parameter
for the motor sizing). The tangential force per rotor pole
however remains in the same order of magnitude between
the 40 ft and 44 ft due the larger diameter and larger pole
quantity. The readiness to operate at 5000 masl will also be
checked both thermally and electrically. ABB’s approach is
to minimize risks by building on the experience gathered
with its operating fleet of 40 ft, 28 MW GMDs, and on the
design of the first 42 ft GMD ever manufactured. This up-
scaling of a well proven design is systematically validated by
state-of-the-art electromagnetic, mechanical, and thermal
simulations as well as tests.
Electrical Design
The electrical motor design is primarily defined by the
motor rated torque, mill diameter, the site elevation,
dynamic behavior, and electromagnetic forces. ABB will
use the same stator winding system and pole concept for
the new generation of large GMDs as is already operat-
ing reliably for 15 years on all GMDs. Roebel bars with
Micadur VPI (Vacuum Pressure Impregnation) system are
used for the stator windings (Figure 4). The rotor poles will
be single units, with the advantage that each rotor pole can
be slightly adjusted to get a perfect runout (Figure 5).
Roebel bars are used in GMDs because of their higher
efficiency compared to standard multi-turn windings. The
Roebel bar undergoes shaping into its final form using an
automatic bending machine. The taping process is pre-
dominantly mechanized, ensuring a consistent application
of insulation through even tape tension and overlapping.
Once insulated the bars undergo full vacuum pressure
impregnation (VPI) with resin. Following a period of excess
pressure, the bars are molded and cured in an oven at ele-
vated temperatures. This insulation technique was devel-
oped over 30 years ago to eliminate voids or gaps in the
insulation thus minimizing the negative impact of partial
discharge. It results in high operational reliability, efficiency
and extended service life as winding insulation faults prac-
tically no longer arise. After this process, the bar is ready
for installation into the stator core slot. All the bars are
electrically tested individually to ensure the highest level
of quality.
The electrical design needs to take into account the
operating altitude of the machine. The air pressure and
density decrease with altitude, this reduces the natural insu-
lation properties of air. Consequently, for a given voltage
level, a larger distance between conductors will be required
compared to operation at sea level. The increased clear-
ance between electrical parts affects both the motor and the
cycloconverter. Hence high-altitude electrical equipment
will need more space. Another effect of altitude is the lower
cooling capacity of the air.
A test was conducted on a mock-up section of the
winding in a barometric chamber that simulates 5000 masl
(see Figure 6). Six bars (three bottom and three top bars, see
Figure 7) produced according to ABB’s standard
manufacturing process were loaded in the chamber
and tested at rated voltage and current. The test confirmed
that the winding design, clearance between the bars and the
insulation was perfectly valid to be installed and operated
at high altitude.
Figure 4. Roebel bars VPI insulated on the full length
Figure 5. Single poles, without welding and individually
adjustable on the mill flange
sea level (masl), creating additional challenges such as the
thermal behavior, voltage distances, transport to site, and
all site services.
Compared to the largest GMD in operation nowadays
– 40 ft, 28MW – building GMDs up to 44 ft, 35 MW for
SAG mills and 32ft, 30MW for ball mills represent up to
30% motor torque increase (which is the main parameter
for the motor sizing). The tangential force per rotor pole
however remains in the same order of magnitude between
the 40 ft and 44 ft due the larger diameter and larger pole
quantity. The readiness to operate at 5000 masl will also be
checked both thermally and electrically. ABB’s approach is
to minimize risks by building on the experience gathered
with its operating fleet of 40 ft, 28 MW GMDs, and on the
design of the first 42 ft GMD ever manufactured. This up-
scaling of a well proven design is systematically validated by
state-of-the-art electromagnetic, mechanical, and thermal
simulations as well as tests.
Electrical Design
The electrical motor design is primarily defined by the
motor rated torque, mill diameter, the site elevation,
dynamic behavior, and electromagnetic forces. ABB will
use the same stator winding system and pole concept for
the new generation of large GMDs as is already operat-
ing reliably for 15 years on all GMDs. Roebel bars with
Micadur VPI (Vacuum Pressure Impregnation) system are
used for the stator windings (Figure 4). The rotor poles will
be single units, with the advantage that each rotor pole can
be slightly adjusted to get a perfect runout (Figure 5).
Roebel bars are used in GMDs because of their higher
efficiency compared to standard multi-turn windings. The
Roebel bar undergoes shaping into its final form using an
automatic bending machine. The taping process is pre-
dominantly mechanized, ensuring a consistent application
of insulation through even tape tension and overlapping.
Once insulated the bars undergo full vacuum pressure
impregnation (VPI) with resin. Following a period of excess
pressure, the bars are molded and cured in an oven at ele-
vated temperatures. This insulation technique was devel-
oped over 30 years ago to eliminate voids or gaps in the
insulation thus minimizing the negative impact of partial
discharge. It results in high operational reliability, efficiency
and extended service life as winding insulation faults prac-
tically no longer arise. After this process, the bar is ready
for installation into the stator core slot. All the bars are
electrically tested individually to ensure the highest level
of quality.
The electrical design needs to take into account the
operating altitude of the machine. The air pressure and
density decrease with altitude, this reduces the natural insu-
lation properties of air. Consequently, for a given voltage
level, a larger distance between conductors will be required
compared to operation at sea level. The increased clear-
ance between electrical parts affects both the motor and the
cycloconverter. Hence high-altitude electrical equipment
will need more space. Another effect of altitude is the lower
cooling capacity of the air.
A test was conducted on a mock-up section of the
winding in a barometric chamber that simulates 5000 masl
(see Figure 6). Six bars (three bottom and three top bars, see
Figure 7) produced according to ABB’s standard
manufacturing process were loaded in the chamber
and tested at rated voltage and current. The test confirmed
that the winding design, clearance between the bars and the
insulation was perfectly valid to be installed and operated
at high altitude.
Figure 4. Roebel bars VPI insulated on the full length
Figure 5. Single poles, without welding and individually
adjustable on the mill flange