what is tan delta test of a power transformer?

The tan delta test of a power transformer measures the insulation’s dielectric losses by evaluating the power factor of the insulation system. During the test, an AC voltage is applied, and the current is measured to determine the phase angle between the voltage and current. The tangent of this angle (tan delta) indicates the insulation’s condition; higher values suggest increased losses and potential insulation degradation, which can lead to transformer failure if not addressed.