Dielectric absorption rate or ratio is a testing parameter used
to determine the opposition to current flow through an insulating
material sometimes expressed as insulation resistance in ohms or
megohms. Testing the integrity of insulation involves measuring its
resistance to current flow across or through it at specific voltage
levels. A high level of resistance indicates that very little
current is escaping through the insulation. Conversely, a low level
of resistance indicates a significant amount of current may be
leaking through and along the insulation.
Similar to capacitive current, absorption current starts out
relatively high and then decreases over time. As the voltage
increases, the absorption level in the insulation decreases. This
gradual change reflects the potential energy stored in and around
the insulation.
The dielectric absorption rate or ratio is the comparison of the
leakage current or insulation resistance over a set time interval.
The end reading divided by the initial reading yields a number
which if less than 1.00 generally indicates faulty insulation.
Another test similar to the dielectric absorption test is the
polarization index ratio. This test is performed in much the same
manner except with a longer time interval.
