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Commissioning
7.3 Testing the insulation resistance and polarization index
7.3
Testing the insulation resistance and polarization index
Hazardous voltage at the terminals
During and immediately after measuring the insulation resistance or the polarization index
(PI) of the stator winding, hazardous voltages may be present at some of the terminals.
Contact with these can result in death, serious injury or material damage.
● If any power cables are connected, check to make sure line supply voltage cannot be
● Discharge the winding after measurement until the risk is eliminated, e.g. using the
Measure the insulation resistance
1. Before you begin measuring the insulation resistance, please read the manual for the
2. Make sure that no power cables are connected.
3. Measure the insulation resistance of the winding in relation to the machine enclosure and
4. Read out the insulation resistance one minute after applying the measuring voltage.
Measuring the polarization index
1. To determine the polarization index, measure the insulation resistances after one minute
2. Express the measured values as a ratio:
Limit values for insulation resistance and polarization index of the stator winding
The following table shows the measuring voltage and limit values for the insulation resistance
and polarization index. These values correspond to the recommendations of IEEE 43‑2000.
70
WARNING
delivered.
following measures:
– Connecting the terminals with ground potential until the recharge voltage drops to a
non-hazardous level
– Connecting the connecting cable
insulation resistance meter you are going to use.
the winding temperature. The winding temperature should not exceed 40° C during the
measurement. Convert the measured insulation resistances to the reference temperature
of 40° C according to the formula in the following table. This thereby ensures that the
minimum values specified can be compared.
and ten minutes.
PI = R
/ R
insul 10 min
insul 1 min
Modern measuring devices display these values automatically following the measurement.
LOHER CHEMSTAR 1PS5
Operating Instructions 03/2014
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