Dielectric Dissipation Factor (Tan-Delta) :
Test method used: IS: 6262-1971 (Reaffirmed 2006)
The Dielectric Dissipation Factor is the ratio of power dissipation in the transformer oil in watts to the product of the effective voltage and current in volt-amperes. It is the tangent of the angle (delta) by which the phase difference between applied voltage and resulting current deviates from p/2 radian when the dielectric of the capacitor consists exclusively of insulating oil. This test reveals the presence of moisture, soluble polar contaminants, ageing products or colloids, resins, varnishes or their products of oxidation in transformer oil.