Megger Baker AWA-IV User Manual page 94

Test Procedures
During the step voltage test, you can evaluate the recorded step leakage current levels for linearity by comparing
the change in leakage current between each step. In the example below, the leakage current increases from 8.80
µA to 12.80 µA—a 4 µA change in current. The next step also changed by 4 µA. This is considered a perfect linear
response because there was no increase in the change in current. The third step had a change in current of 5.4 µA.
While this increase in the change in current is not ideal, it is still considered linear. The current departs from a linear
relationship when this change in current at least doubles.
In step five, we see that the current has changed by 10.2 µA. The previous step had only changed by 5 µA, so the
increase in the change in current has more than doubled. This greater increase in current is due to a significant drop
in the insulation resistance value.
While this test has not failed, the departure from linearity could be used to prompt you to stop the step voltage test
because reduced insulation integrity has been detected.
Fig 87: Example Step Voltage test illustrating increase in current change.
Time(s) Volts (V)
60 3300
60 4320
60 5350
60 6360
60 7350
60 8320
60 9360
82 Baker AWA-IV 71-015 EN V16 User Guide
I(µA) Megohms
8.80 378
12.80 338
16.80 318
22.20 286
27.20 270
37.40 222
51.80 181
IR@40C Difference between intervals
267
239 12.8 - 8.8 = 4
224 16.8 - 12.8 = 4
202 22.2 - 16.8 = 5.4
190 27.2 - 22.2 = 5
156 37.4 - 27.2 =
127 51.8 - 37.4 = 14.4
10.2 DOUBLED
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