What would you suspect if you saw that the twice-line-frequency peak was high?

A high twice-line-frequency peak in vibration analysis indicates issues related to electrical imbalances or mechanical misalignments within the machine. This specific frequency is often associated with irregularities in the magnetic field, which can arise from a variety of mechanical and electrical conditions.

When considering soft foot, this can lead to misalignment and uneven loading, which could produce a twice-line-frequency peak in the vibration spectrum. The condition affects how the base of the machine sits on its foundation, potentially causing vibration irregularities at this frequency.

With regard to eccentricity in the stator, if the stator is not properly aligned or is eccentric, it can cause the rotor to experience varying magnetic forces, which can also lead to spikes at the twice-line frequency.

Loose windings or laminations can create gaps in the magnetic circuit, leading to increased vibration due to unsteady magnetic forces as the rotor passes, thereby contributing to high peaks at twice-line frequency as well.

Given that all these issues can manifest as a high twice-line-frequency peak, it's logical to conclude that any of the conditions mentioned could lead to this observation. Thus, acknowledging that any of these factors could be responsible for the vibration issue makes this answer comprehensive.