what is the significance of tan delta testing?explain the
theory?

Answer Posted / koushik goswami

Ideally an insulation (be it across a cable or a electrical
switch gear) should be of infinite resistance. That is
ideally if voltage is applied across insulation no current
should pass through (considering resistive current only).
Now there is another aspect of an insulation. An insulation
is also a capacitor (two plates seperated by dielectric)
and hence there must be some current (opf course ac
current) that will flow if voltage is applied acroos
insulation (this is capacitive current). Now the ration of
the resistive current (which shoud ideally be zero) and the
capacitive current is called loss tangent or tan delta and
is measurable. So if tan delta is measured we are actually
get an idea of the resistive current through the
insulation. A high tan delta indicates high resistive
current and that means insulation is detoriating.

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