The dielectric absorption ratio is the ratio of two time-resistance readings such as a 60-second reading divided by a 30-second reading. If the ratio is a 10-minute reading divided by a 1-minute reading, the value is called the polarization index. The principle behind the test is that the resistance would increase with time as the capacitive and polarizing currents begin to subside.
Unlike spot tests that are relative to specific conditions such as temperature each time that the test is performed, ratios of insulation resistance (Dielectric Absorption Ratio) that are taken at essentially the same time and temperature require no correction factor for comparison purposes.
When a testing device is used with any insulation system, there are basically three components of current.
- Capacitive charging current: When DC voltage is applied between the earth and the insulation system,it draws a higher current in the beginning of the test, and then quickly drops off as the capacitive component of the insulation system become charged to full voltage.
- Dielectric absorption current: It is the polarizing current that results from the alignment of molecules within the insulation. It is initially a higher value, but slowly falls off as molecules become polarized.
- Leakage Current: A proportionally small steady state current that flows through and across the surface of electrical insulation.
After understanding the basics of the dielectric absorption testing, you can get the right testing device according to your needs. Try electrical test equipment rental to save money, instead of purchasing the devices.
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Editor’s Note: This post was originally published on May, 2013 and has been updated freshness, accuracy and comprehensiveness.