A recent study of generator loss data over the last 10 years shows that the claim amount per loss caused by stator endwinding vibration is almost 50% of the total paid out for all causes!!
The stator endwinding is the winding extending beyond the stator core. Due
to design requirements the endwinding from the slot exit can be quite long
(sometimes greater than 2m), especially on 2-pole machines. This results in a
cantilever effect when operational forces are applied to the windings. The
primary forces are due to the electromagnetism effect of 2 parallel current
carrying conductors at line frequency resulting in a force at twice line
frequency (100/120Hz). On some machines the centrifugal forces (at once
turning speed) are coupled to the stator including the endwindings (50/60Hz
for 2-pole synchronous machines, 25/30Hz for 4-pole, etc). Both, the Figure 1 – Failed phase connection [1] turning speed and the electromagnetic forces are predominantly in the
radial direction (between the rotor and the stator and between the top and bottom bars). However there is also a significant force in the tangential direction (circumferential around the endwinding basket between two adjacent bars).