Eaton QD5 Manual page 16

Contact inspection
Tap-changer contacts are exposed to combination of
electrical, mechanical and thermal conditions that result
in deterioration. Erosion at the points subjected to arcing
duty is the most visible indication of wear. Figures 19 and
20 illustrate typical contact erosion patterns resulting from
normal service. Contacts at the end of life stage shown in
Figures 21 and 22 must definitely be replaced. The figures
below show actual contacts after various stages of contact
erosion.
New contacts
Figure 17. QD5 tap-changer movable contact.
Intermediate life stage
Figure 19. QD5 tap-changer movable contact.
End of contact life stage
Figure 21. QD5 tap-changer movable contact.
12 QD5 QUIK-DRIVE TAP-CHANGER INSTALLATION AND MAINTENANCE INSTRUCTIONS MN225012EN March 2016
Figure 18. QD5 tap-changer stationary contact.
Figure 20. QD5 tap-changer stationary contact.
Figure 22. QD5 tap-changer stationary contact edge.