2.7 D - Dissipation Factor or Tan-d
The parameter D is most often used as a measurement of the losses in a
capacitor. It is analogous to Q for a transformer winding.
For this equivalent circuit the Dissipation Factor D is defined as:
For a given capacitance, the lower the equivalent series resistance, the
lower is the value of the dissipation factor or tanδ, i.e. the 'better'
The dissipation factor test would normally be used for capacitors of all
A D factor test will help to determine that the capacitor has been
To measure Dissipation Factor, the tester applies an ac voltage across
the selected winding, and measures the voltage across and the current
through the winding.
Using harmonic analysis, the measured voltage is divided by the current
to obtain a complex impedance from which the Dissipation Factor is
Choosing the test signal
For optimum accuracy and performance, use the test conditions chosen for
capacitance in a later section of this chapter.