Wedge Deflection / Mapping
Wedge looseness is a dangerous condition for two reasons, firstly it may foul with rotor causing mechanical damage and secondly the coils are not held tightly in the slots. This may lead to coil surface erosion due to its rubbing with core and eventually partial discharges in slots. While these effects can be detected by the diagnostic test. In the presence of ripple springs the extent of wedge looseness is measured with dial guage deflection by applying calculated pressure.
Alternatively Generator with no ripple springs are tested by performing wedge mapping test to identify which wedges are partially or completely loose/damaged.The tightness of wedges is checked by tapping each wedge in all the slots, with a hammer and listening to the emanating sound. A map is prepared to represent an overall picture of wedge tightness. Prognosys also provides analysis regarding the criticality and looseness percentage. Prognosys gives colorful map display identifying loose wedges and also analysis of the severity of wedge looseness and effect on the machine.