An extremely important capability of EMPATH testing is the resolution. The ~26,500 lines (all other ESA type devices are under 17k lines – EMPATH is not a simple ESA device) allow us to review fine differences in frequency including pole pass frequencies of unloaded and uncoupled motors. In this case study an 800hp, 4160 Volt motor is tested both on and off (by-pass) a Variable Frequency Drive (VFD).
Testing for the VFD was performed with current-only testing at the motor itself as we were also performing motion amplification simultaneously. As the motor was uncoupled and this was part of a more significant analysis, we also performed the work in by-pass with the EMPATH connected to the back of the Multilin, as shown in Figure 2.
Figures 3 and 4 represent the findings that, with additional testing, were determined to be accurate including a loose rotor cage, and some other conditions that we will not explore here. However, it can be noted that the combined use of motion amplification and EMPATH were able to determine that the conditions that were being explored did not include the motor base.
Figure 3, which is from the VFD dataset includes noise from the internal fans and some motor unbalance. The red arrows relate to the pole pass frequency which often indicates a rotor-bar related condition.
On Figure 4, you will notice that there are tight pole pass frequency sidebands around the static eccentricity peaks. With the high resolution of the EMPATH system, the ability to detect this is possible. In this case, it has to do with the looseness of the rotor bars – there may also be high resistance in the connections between the bars and the end-rings.
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