The slot wedging system serves that the bars remain tight in the slots and that they are permanently protected from possible vibrations in order to avoid damage to the insulation.
To prevent loosening of the stator bars in the slot , top ripple springs are provided below the slot wedges.
The ripple springs are designed so that the pulsating magnetic forces due to load cannot cause any unduly high bar vibration It is recommended to check the stator during each overhaul involving a with drawl of the generator rotor.
The check to be performed is to ensure that the top ripple spring still provide sufficient pre loading.
The devices used for this purpose utilizes hydraulic depression of the slot wedges.
The measured slot wedges movement which corresponds to the residual spring travel of the top ripple spring, helps to determine the existing pre loading exerted by the top ripple spring.
