Is it safe to cycle an LTC on a de-energized xfmr with the oil drained from the tank? What about testing u.der those conditions?
It is generally safe to cycle the LTC with the oil drained. This is how you perform an internal mechanical inspection. You can run certain tests under these conditions, usually low-current DLRO or other small measurements, not HV insulation testing as this would require the oil. Here are some videos of a LTC operation: