Cold Start Performance of Transformers Filled with High Molecular Weight Hydrocarbon Liquid

Two high loss 167 kVA pole type transformers were filled with conventional mineral oil and cold start tested at -30??C under full load. The two units were subsequently drained, retrofilled with a high molecular weight hydrocarbon (HMWH) fluid, and then retested at -30??C. The units were identical, except one used corrugated fins for cooling and the other used radiator panels. Thermocouple temperature readings indicated that the units were successfully cold-started with both types of fluid. When filled with HMWH fluid, maximum winding temperatures of 58??C and 52??C were recorded for the finned and radiator transformers respectively. These winding temperatures are well below the 105??C maximum continuous rating of the insulation (65??C rise over a 40??C ambient). No thermal runaway occurred. Indeed, the results indicate that HMWH filled transformers can tolerate substantial overloads during both startup and continuous operation at low ambient temperatures.