Experimental Investigation of Breakdown Voltage of Old and New Transformer Oil Under Uniform and Non-Uniform Field Conditions

Power transformers are the key components of modern power system network. Oil is used in a transformer for insulation and cooling purpose. As transformer undergoes electrical, thermal, and chemical distress throughout their lifetime, the oil deteriorates. In the present research, the breakdown voltage of newly purchased transformer oil and old oil, collected from a transformer serving for 10 years, has been investigated through laboratory experiments. Two types of electrode pairs, plane-plane (uniform field) and point-plane (non-uniform field) have been used to observe the behavior of both insulating samples under uniform (theoretical) and non-uniform (real life) field situation. An interesting observation is the continuous flow of current through the old oil sample for non-uniform field condition; which may cause the rise of temperature of the oil as well as the transformer; thus the old transformer is at high risk of fire hazard. As expected the breakdown strength of new oil under uniform field is found to be higher than that of the old oil under non-uniform field condition.