What is the density of transformer oil at operating conditions?

Density at operating conditions depends on the oil type and temperature. Mineral oil density is higher at low temperature and decreases as temperature rises. Because transformer top oil temperatures can vary widely with load and ambient, operating density is typically estimated using the reference density from the data sheet and applying thermal expansion correction. For engineering calculations such as oil volume expansion and conservator sizing, use the manufacturer provided density versus temperature curve rather than a single fixed value.