Dielectric Loss Angle Test (DLA)

Dielectric Loss Angle (DLA) test, also known as Double Power factor test (DDF), is used to determine conditions of an insulation medium in the high voltage apparatus.

A virtue of this test is that it is non-destructive, because the voltage applied to the insulation need not exceed the rated value of the system. The test method is described in IEEE Standard 286 (latest edition 2000). An equivalent international standard for the same test is IEC 60894, published early in 1987. In a perfect capacitor, the voltage and current are phase shifted 90 degrees and the current through the insulation is capacitive. If there are impurities in the insulation, like internal voids or insufficient resin penetration, the resistance of the insulation decreases, resulting in an increase in resistive current through the insulation. It is no longer a perfect capacitor. The current and voltage will no longer be shifted 90 degrees. It will be something less than 90 degrees. The extent to which the phase shift is less than 90 degrees is indicative of the level of insulation contamination, hence quality/reliability. This “Loss Angle” is measured and analyzed.

By measuring IR/IC, we can determine the quality of the insulation medium. In a perfect insulating material, the angle would be nearly zero. An increasing angle indicates an increase in the resistive current through the insulation, meaning contamination. The greater the angle, the worse the insulation.

Application includes: Transformers, Current and Voltage Transformers, Bushings, Generators, Motors and Surge arrestors.