ABSTRACT
Method D877. The oil must have a minimum breakdown voltage
3. After assembly, pressurize the transformer to 2 psig by adding dry nitrogen. Check the transformer for leaks.
4. For transformers rated 115 kV and above, after waiting for a 24 h period, make a dew-point check to determine the dryness of the transformer insulation. For new transformers and transformers in warranty, refer to the manufacturer’s instructions for acceptable dew-point readings. For transformers not in warranty, refer to Table 8.1.5. If it does not pass dew-point test, a hot oil dryout is required. After dryout, repeat step 4.
