Dielectric Frequency Response (DFR) testing delivers a very reliable and accurate moisture assessment of the insulation and the conductivity of the oil.

A thorough review of DFR elucidates why this is a better tool for moisture assessment than traditional moisture in oil measurement, which deduces the moisture content in cellulose from the measured moisture in oil. Megger’s IDAX is a best-in-class dielectric response analyzer and the only instrument that can perform true FDS measurements (which is the preferred DFR method due to its robustness against noise) all the way down to 0.1 mHz in record time. A noteworthy accessory for the IDAX is the VAX, an amplifier that boosts the output signal of the IDAX to 2 kV, which may be important for low capacitive specimens, particularly CTs, to obtain meaningful moisture measurements.