Doble

Doble test is a test of transformers. It is named based on the earlier manufacture of testing equipment.

Doble equipment puts a 2.5 kV or 10 kV AC signal on the transformer or other test specimen, then carefully measures signals proportional to the watts and VA. From that you can calculate, or read directly on the fancier instruments, the power factor of the current flowing into the insulation. A perfect insulation only has capacitive current flowing, power factor zero. Wet, dirty or degraded insulation will have resistive leakage current, raising the power factor. 1% or lower is good, but like megger readings a lot is relative.