what is c&df test of transformer?

The C&D test, or Capacitance and Dissipation Factor test, is used to assess the insulation condition of a transformer. It measures the capacitance and the power factor (dissipation factor) of the transformer windings. A high dissipation factor indicates insulation degradation, which can lead to failures. This test helps ensure the reliability and longevity of transformers by identifying potential insulation issues before they result in operational problems.