Dielectric absorption ratio (DAR)

What is the dielectric absorption ratio (DAR)

The dielectric absorption ratio (DAR) represents an important parameter for plants or equipment equipped with insulating materials in which the absorption current decreases rapidly. The measurement of the insulation resistors at 30 and at 60 seconds may be sufficient to qualify the insulation status.

Standards associated with this test

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Non ci sono normative per questa macchina.

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How the dielectric absorption ratio is defined

The DAR is defined as follows:

DAR = R insulation at 60 sec. / R insulation at 30 sec.

The DAR test must be carried out by applying the same continuous voltage values used to verify the insulation resistance (500 Vdc for machines with rated voltage up to 1000 V., 1000 Vdc for those with rated voltage higher than 2500 V.), for a period of 10 minutes.

In practice, the test voltage is applied between the windings connected to each other, and the grounding; after 30 seconds, the instrument reads and stores the detected MWvalue. The test then continues for 60 seconds and the final measured value is compared to the initial one.

  • If the value of the ratio is greater than6, the insulation is good.
  • For values between 25 and 1.6, the insulation is at the limit of its characteristics.
  • For values below 25, the insulation is critical and requires urgent maintenance

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