For a 2500KVA 12.47KV to 480V transformer, what is the issue with cracking in the epoxy?
The short answer is that there will be no issue for cracking any of ABB’s vacuum cast coil technology.
Some further details:
The perception of vacuum cast coil cracking stems from back in the late 80s early 90s when the technology was beginning to become widely acceptable and many manufacturers adopted the product. There were some issues of “not all coil designs being created equal.” And even ourselves had some issues with this during that time. Since then, we have devoted much effort to correct this issue by adjusting thermal coefficient rates and increasing the amount of support material embedded in the epoxy itself. Now, all ABB primary cast coils come standard with the ability to pass IEC’s C2 requirement of unrestricted use at -25C. Upon request, we can even meet that requirement down to -50C.
Now, from field installation data, true cast LV (< 1000V) coils tend to have a rare issue of small cracks at larger ratings (> 5MVA). This comes from the large bus bar leads that protrude from the windings for connection. There is, on a rare occasion, a chance to form hair line cracks at these lead outs. Mostly due to excess stress (heavy cable, improperly aligned bus, etc.) on the leads when connected into the system and then energized. Typically, these do not pose a major threat because of the voltage class and can be easily repaired in the field, if so desired. An easy way to avoid this occurrence is to ask for a flexible connection point to the LV leads.
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