XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3853
These changes were chosen to be implemented when the
utility was performing maintenance on the network. This
resulted in a unique opportunity where the network tran-
sients could be anticipated due to planned switching of
equipment upstream. The predictable nature of these tran-
sients over a duration of a week provided valuable data that
was used to fine tune the system settings.
Results
Figure 9 demonstrates the ridethrough behaviour of Ball
Mill 2 during a transient event. The red highlighted area
shows the currents being drawn by the drive when it is act-
ing as an uncontrolled rectifier. The current drops to almost
zero as a consequence of the reduction of the output torque
provided to the motors by the inverters. Following the
detection of a recovered network, the drive slowly ramps
up the current demand. The higher currents seen later in
the trend are due to the increased power demand of the
system to return to the normal DC voltage setpoint and
normal motor speed.
The effect of the new settings on the mill speed can be
seen in Figure 10. The recovery time of each mill is different
to provide sufficient time for the network to recover. The
power demands of each mill during this event can be seen
in Figure 11.
VARIABLE SPEED OPERATION
The SAG Mill was designed to operate at a Mill speed of
9.88 rpm, and the Ball Mill was designed to operate at a
speed of 11.89 rpm. The Mill speed is an important factor
in the grinding process and can affect the overall param-
eters of the process. The inherent ability of the variable fre-
quency drive to vary the speeds of the Mills are regularly
used at Detour Lake Mine. The Mills have been modified
to operate at a higher speed. The speed profiles of the 4
Mills for a period of 4 months is shown in Figure 12a–d.
Figure 8. The DC voltage overshoots when the primary voltage recovers. The constant power demand of the motors causes the
current (light blue line) to overshoot to maintain the speed of the mill
These changes were chosen to be implemented when the
utility was performing maintenance on the network. This
resulted in a unique opportunity where the network tran-
sients could be anticipated due to planned switching of
equipment upstream. The predictable nature of these tran-
sients over a duration of a week provided valuable data that
was used to fine tune the system settings.
Results
Figure 9 demonstrates the ridethrough behaviour of Ball
Mill 2 during a transient event. The red highlighted area
shows the currents being drawn by the drive when it is act-
ing as an uncontrolled rectifier. The current drops to almost
zero as a consequence of the reduction of the output torque
provided to the motors by the inverters. Following the
detection of a recovered network, the drive slowly ramps
up the current demand. The higher currents seen later in
the trend are due to the increased power demand of the
system to return to the normal DC voltage setpoint and
normal motor speed.
The effect of the new settings on the mill speed can be
seen in Figure 10. The recovery time of each mill is different
to provide sufficient time for the network to recover. The
power demands of each mill during this event can be seen
in Figure 11.
VARIABLE SPEED OPERATION
The SAG Mill was designed to operate at a Mill speed of
9.88 rpm, and the Ball Mill was designed to operate at a
speed of 11.89 rpm. The Mill speed is an important factor
in the grinding process and can affect the overall param-
eters of the process. The inherent ability of the variable fre-
quency drive to vary the speeds of the Mills are regularly
used at Detour Lake Mine. The Mills have been modified
to operate at a higher speed. The speed profiles of the 4
Mills for a period of 4 months is shown in Figure 12a–d.
Figure 8. The DC voltage overshoots when the primary voltage recovers. The constant power demand of the motors causes the
current (light blue line) to overshoot to maintain the speed of the mill