What are the methods testing insulating oil?
For in-service equipment in particular, there are many test techniques for evaluating the condition of the insulating oil. If the technique of dissolved gas analysis is excluded, oil tests can be divided into two basic groups.
The first group includes tests that are concerned with the immediate condition and acceptability of the insulation in an item of electrical equipment. This group includes dielectric breakdown voltage testing as well as moisture measurement by the Karl Fischer (KF) method, and determination of insulation condition by measuring the dielectric dissipation factor.
The second group includes tests that look at the degree of degradation and aging of the equipment's insulation system. These tests include interfacial tension, acidity (neutralisation value), resistivity and visual determination of colour and appearance of the insulating oil.
While all of these tests are useful in particular circumstances, the most convenient and most universally applicable is dielectric breakdown voltage testing.
