The most easily observable symptoms of a faulty field winding are vibrations and internal stator currents.
Vibrations
When an uneven magnetic field is generated by the rotor, the result is unbalanced magnetic pull around the circumference of the air gap. This will pull the rotor in the opposite direction of the faulty pole, with a corresponding increased pull on the stator. The direction of the pull will rotate with the rotor, causing vibrations in the machine. Depending on the magnitude of the pull and the rigidity of the machine, the air gap will also be reduced in the direction of the pull. Since the force of the magnetic pull is inversely proportional to the square of the air gap length, this will further increase the magnetic force opposite to the faulty pole.
Internal stator currents
An uneven magnetic field will induce different voltages in the circuits of generators with multiple stator windings, giving rise to internal stator currents. In extreme cases, these currents can cause a machine fitted with protection against such currents to trip. In other cases, internal stator currents will increase the heat of the stator winding.