IR Testing Using DAR (Dielectric Absorbtion Ratio) Time Mode

Google " IEEE standard 43-2000" and pick a site, that will help you understand PI.

Dear zhafran,

DAR(Dielectric Absorption Ratio) is the ratio of reading of insulation resistance values measured after 15 secs. and after 1min.(60secs.).The DC TEST VOLTAGE MUST BE CONTINUING during the whole period of measurement; at the end of the test,the DAR value can be calculated or directly displayed by the test equpment. Similarly,PI(Polarisation Index) is the ratio of Insulation Resistance values maesured after 1min.(60secs.) and 10min.(600secs.)The DC TEST VOLTAGE MUST BE CONTINUING during the whole period of measurement; at the end of the test,the PI value can be calculated or directly displayed by the test equpment.

Actually,when you are injecting DC voltage to the motor for the above testing , capacitance formed due to the insulation system, is charged up. It is to be noted that,the capacitane has to be charged up in the first 15 secs time in case of DAR mode and similarly in PI mode, capacitance has to be charged up in first 1min.(60secs.) time. Therefore, the ratio of IR values in the the above two type of tests(depending on formation of capacitances/charging of capacitor, vis-a-vis,alingnment of positive and negative charges towards negative and positive plates respectively). So by this measurements,condition of insulation system can be monitored.

Thanks,

Manindra