Oil Tan Delta test is also known as the Loss Tangent or Dielectric Dissipation Factor measurement. Tan Delta may be defined as the measurement of the cosine of the phase angle or the sine of the loss angle. It is basically the measurement of the leakage current through the oil, which in turn is a measure of the contamination or deterioration of the oil. The oil is non-polar and most contaminants are polar, enabling a dipole action, which this test depends upon. A normal degree of refining will result in a low value for the power factor. The presence of contaminant such as engine oil will easily be detected with this parameter.