Method A is the older method, which uses conditions of 19 hours at 140°C. Method B is the newer method, which uses conditions of 48 hours at 150°C
Testing the oil in load tap changers (LTC's) provides valuable information on the operation of the unit. Monitoring conditions between preventive maintenance inspections is a critical step in preventing expensive maintenance problems and even unplanned outages. This first article in a series will address the aging of mineral insulating oil in an LTC.
You cannot just change the oil to lower the acid number to an acceptable level in place of a hot oil cleaning. Changing the oil will not permanently reduce the oxidation byproducts in the solid insulation. It is not an appropriate maintenance solution for lowering a high acid number.