XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3785
UMP in turn affects the air gap around the circumference
which becomes oval. ABB’s stator stiffness ensures that even
at the maximum UMP value, the air gap will remain below
the alarm level. The stress calculation checks that critical
mechanical components such as the pole to mill interface,
and stator electrical core to frame connection are not sub-
ject to excessive stresses. It has also been computed that
the new generation of large GMDs will need additional
anchor bolts and reinforced sole plates to cope with the
larger torque.
The rotation of the GMD creates dynamic loads which
induce vibrations in the ring motor that are in addition
to the static and steady loads. It is critical to ensure that
the vibrations remain within an acceptable level. These
dynamics loads arise specifically from the interaction of
the electromagnetic fields between the poles and the stator
in the air gap. This electromagnetic excitation has a fun-
damental frequency equal to the pole passing frequency
(PPF). The objective of the modal analysis is to evaluate
the natural frequencies of the motor against this PPF at
the maximum mill speed. The critical natural frequencies
are the so called 4-node modes, which are the first in-plane
modes and a spatial mode shape resembling an ellipse, as
shown below in Figure 10.
The ABB ring motors are designed to have the relevant
4-node (fist in-plane) modes above the PPF. This crite-
rion enforces minimum stiffness requirements in the ring
motor structure that effectively limits the contribution of
Figure 10. Finite element analysis showing the stator displacement for the 4-node mode
UMP in turn affects the air gap around the circumference
which becomes oval. ABB’s stator stiffness ensures that even
at the maximum UMP value, the air gap will remain below
the alarm level. The stress calculation checks that critical
mechanical components such as the pole to mill interface,
and stator electrical core to frame connection are not sub-
ject to excessive stresses. It has also been computed that
the new generation of large GMDs will need additional
anchor bolts and reinforced sole plates to cope with the
larger torque.
The rotation of the GMD creates dynamic loads which
induce vibrations in the ring motor that are in addition
to the static and steady loads. It is critical to ensure that
the vibrations remain within an acceptable level. These
dynamics loads arise specifically from the interaction of
the electromagnetic fields between the poles and the stator
in the air gap. This electromagnetic excitation has a fun-
damental frequency equal to the pole passing frequency
(PPF). The objective of the modal analysis is to evaluate
the natural frequencies of the motor against this PPF at
the maximum mill speed. The critical natural frequencies
are the so called 4-node modes, which are the first in-plane
modes and a spatial mode shape resembling an ellipse, as
shown below in Figure 10.
The ABB ring motors are designed to have the relevant
4-node (fist in-plane) modes above the PPF. This crite-
rion enforces minimum stiffness requirements in the ring
motor structure that effectively limits the contribution of
Figure 10. Finite element analysis showing the stator displacement for the 4-node mode