Insulation Resistance Test

Yes, this is typical of testing insulation resistance of long transmission lines. You have to let them charge.

You must also discharge the lines in substations even after the power is off.

This sometimes requires leaving jumper cables attached for hours.

The capacitance discharge of high voltage wiring and transformers can be deadly.

Theoretically, a capacitor is never fully charged or discharged,but it will get close enough for practical purposes.

Insulation resistance and polarization imdex test

https://sdvelectrical.blogspot.com/2019/05/insulation-resistance-and-polarization.html

This is one graph from "Stitch in Time", showing initial currents.

http://eecoonline.com/motor-repair-best-practices-polarization-index-test/_

It looks like you are applying enough potential during your test to use a polarization index test method to evaluate the insulation condition.

This could be an expedient method to evaluate the insulation, though the fact that it charges up shows the insulation is good. If you use a lower voltage for the test, the charging effect will not be as noticeable. This appears to be a large machine or a high application test voltage. My experience in observing similar circumstances is 4000 volts on a 3000 hp machine, open frame engine type synchronous salient pole machine.

Read the manual.

You have not given the details of electrical equipment under test (I suppose it is a motor driving the compressor). Please give details of equipment, its rated voltage, type and class of insulation and test voltage. Then it would me easier to analyse the conditions.

PI is a Polarization Index run for 10 min at a particular voltage (function of rate voltage of unit) in order to qualify the electrical insulation per IEEE 143.

The test button is to be held till the IR value stabilises.

It is a good sign that the I value is increasing. If you can read 1-min and 10-min IR values, the ratio of 10-min value to 1-min value is an index of Insulation healthiness. This is called Polarisation index (PI).

The ABB motor manual says PI of 2 and above means insulation is good.

If the insulation value improves after holding the test button of the high voltage insulation tester, it shows that the insulation system is OK.The insulation resistance improves as the charging current decays down if the insulation system is OK. The insulation resistance taken after one minute fairly gives the reading of the insulation.

To ensure the healthiness of the system Polarization Index Test can be conducted.The polarization index is the ratio of 10 Minutes IR Value to one minute IR Value. If PI is greater than 2 the insulation system is OK.

Read More:Polarization Index Test