XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3783
Thermal Design
The conversion of electrical power into mechanical power
is necessarily accompanied by losses which generate heat in
the stator and rotor. This heat must be dissipated to limit
the temperature rises of the electrical components which
would otherwise decrease the lifetime of the electrical
insulation. For this reason, all ABB GMDs are designed
to maintain the maximum temperature rise below 80°C
according to IEC60034-1 standard. The existing 28 MW
GMDs for 40 ft and 42 ft SAG mills, as well as the exist-
ing 22 MW GMDs for 28 ft ball mills use a radial cooling
configuration which ensures an optimal and uniform cool-
ing of the electrical core. This is a forced, closed ventilation
circuit where two water to air heat exchangers installed at
the bottom of the GMD cool the air (Figure 8) which is
then blown into the rotor poles and stator before returning
to the heat exchangers (see Figure 9).
Increasing the size and power of a GMD requires pro-
portionately more cooling. This is easily solved at sea level
by keeping the radial cooling configuration and selecting
larger cooling units. The lower air density at 5000 masl
decreases the cooling capacity of the air, so to maintain suf-
ficient heat dissipation, one could lower the inlet cooling
water temperature, increase the number of cooling air ducts
in the electrical core, or increase the air flow. Lowering the
inlet water temperature most often can only be achieved by
using additional chillers, and at the expense of additional
energy consumption. Low cooling water temperature may
also lead to condensation issues or power derating in case
the water temperature cannot constantly be supplied low
enough. Increasing the number of air ducts negatively
impacts the electromagnetic behavior of the electrical core.
Finally, the size of the cooling fans and volume of the air
flow is limited due to space constraints. Thus, the required
heat dissipation at high altitude is achieved by an optimiza-
tion of several parameters. The machine is electrically over-
sized to limit the temperature at the hottest spot, which
most of the time appears to be in the poles. At the same
time, the cooling fans and air flow through the electrical
parts are designed for maximum heat dissipation.
The electromagnetic and thermal computational mod-
els used for the design of the 44 ft, 35 MW GMD have
been validated by the GMDs already in operation.
Mechanical Design
A 35 MW gearless motor will have larger and heavier elec-
trical key components than current operating units. Hence,
all the supporting structures such as stator frame, mill
flange, and foundation will need to be reinforced for the
resulting higher static and dynamic loads.
The mechanical design of a ring motor is carried out in
two steps. First, only the ring motor is considered and the
structural integrity of its main components, stator frame,
poles, pole to mill interface and anchoring system are evalu-
ated at nominal operation, fault conditions (short circuit),
and during seismic events. A complete finite element analy-
sis (FEA) validates the stiffness, stress level and dynamic
behavior of the ring motor. The static and dynamic forces
are transmitted from the motor to the mill, foundations
and soil. Therefore, the second step is an overall system
analysis of the ring motor, the mill, foundations and soil
carried out to confirm the stability of the air gap – the dis-
tance between the rotating poles and the stator windings
– and dynamic behavior of the complete system.
Figure 6. Test of the mock-up in the barometric chamber Figure 7. Mock-up section of the winding consisting of three
top and bottom bars
Thermal Design
The conversion of electrical power into mechanical power
is necessarily accompanied by losses which generate heat in
the stator and rotor. This heat must be dissipated to limit
the temperature rises of the electrical components which
would otherwise decrease the lifetime of the electrical
insulation. For this reason, all ABB GMDs are designed
to maintain the maximum temperature rise below 80°C
according to IEC60034-1 standard. The existing 28 MW
GMDs for 40 ft and 42 ft SAG mills, as well as the exist-
ing 22 MW GMDs for 28 ft ball mills use a radial cooling
configuration which ensures an optimal and uniform cool-
ing of the electrical core. This is a forced, closed ventilation
circuit where two water to air heat exchangers installed at
the bottom of the GMD cool the air (Figure 8) which is
then blown into the rotor poles and stator before returning
to the heat exchangers (see Figure 9).
Increasing the size and power of a GMD requires pro-
portionately more cooling. This is easily solved at sea level
by keeping the radial cooling configuration and selecting
larger cooling units. The lower air density at 5000 masl
decreases the cooling capacity of the air, so to maintain suf-
ficient heat dissipation, one could lower the inlet cooling
water temperature, increase the number of cooling air ducts
in the electrical core, or increase the air flow. Lowering the
inlet water temperature most often can only be achieved by
using additional chillers, and at the expense of additional
energy consumption. Low cooling water temperature may
also lead to condensation issues or power derating in case
the water temperature cannot constantly be supplied low
enough. Increasing the number of air ducts negatively
impacts the electromagnetic behavior of the electrical core.
Finally, the size of the cooling fans and volume of the air
flow is limited due to space constraints. Thus, the required
heat dissipation at high altitude is achieved by an optimiza-
tion of several parameters. The machine is electrically over-
sized to limit the temperature at the hottest spot, which
most of the time appears to be in the poles. At the same
time, the cooling fans and air flow through the electrical
parts are designed for maximum heat dissipation.
The electromagnetic and thermal computational mod-
els used for the design of the 44 ft, 35 MW GMD have
been validated by the GMDs already in operation.
Mechanical Design
A 35 MW gearless motor will have larger and heavier elec-
trical key components than current operating units. Hence,
all the supporting structures such as stator frame, mill
flange, and foundation will need to be reinforced for the
resulting higher static and dynamic loads.
The mechanical design of a ring motor is carried out in
two steps. First, only the ring motor is considered and the
structural integrity of its main components, stator frame,
poles, pole to mill interface and anchoring system are evalu-
ated at nominal operation, fault conditions (short circuit),
and during seismic events. A complete finite element analy-
sis (FEA) validates the stiffness, stress level and dynamic
behavior of the ring motor. The static and dynamic forces
are transmitted from the motor to the mill, foundations
and soil. Therefore, the second step is an overall system
analysis of the ring motor, the mill, foundations and soil
carried out to confirm the stability of the air gap – the dis-
tance between the rotating poles and the stator windings
– and dynamic behavior of the complete system.
Figure 6. Test of the mock-up in the barometric chamber Figure 7. Mock-up section of the winding consisting of three
top and bottom bars