Power Factor dielectric loss
Power factor indicates the dielectric loss (leakage current) of the oil. This test may be completed by the DGA laboratories. It may also be completed by Doble testing. A high power factor indicates deterioration and/or contamination by products, such as water, carbon, or other conducting particles; metal soaps caused by acids (formed as mentioned above); attacking transformer metals; and products of oxidation. The DGA labs normally test the power factor at 25 ºC and 100 ºC. Doble information  indicates that the inservice limit for power factor is less than 0.5% at 25 ºC. If the power factor is greater than 0.5% and less than 1.0%, further investigation is required; the oil may require replacement or fullers earth filtering. If the power factor is greater than 1.0% at 25 ºC, the oil may cause failure of the transformer; replacement or reclaiming is required. Above 2%, oil should be removed from service and replaced because equipment failure is imminent. The oil cannot be reclaimed.