Stator Winding Insulation Resistance Measurement - ABB AMA Series Manual

Manual for Induction Motors and Generators

7.6.4.4 Stator winding insulation resistance measurement

82 - Maintenance
The insulation resistance is measured using an insulation resistance meter. The test voltage is
1000 VDC. The test time is 1 minute, after which the insulation resistance value is recorded.
Before the insulation resistance test is conducted, the following actions must be taken:
• Check that the secondary connections of the current transformers (CT's), including spare
cores are not open. See Figure 7-7 Connections of the stator windings for insulation
resistance measurements
• Verify that all power supply cables are disconnected
• Verify that the frame of the machine and the stator windings not being tested are earthed
• The winding temperature is measured
• All resistance temperature detectors are earthed
• Possible earthing of voltage transformers (not common) must be removed.
The insulation resistance measuring should be carried out in the terminal box. The test is usually
performed to the whole winding as a group, in which case the meter is connected between the
frame of the machine and the winding; See Figure 7-7 Connections of the stator windings for
insulation resistance measurements. The frame is earthed and the three phases of the stator
winding remain connected at the neutral point, see Figure 7-7 Connections of the stator
windings for insulation resistance measurements.
If the measured insulation resistance of the whole winding is lower than specified, and the phase
windings can easily be disconnected from each other, each phase can also be measured
separately. This is not possible for all machines. In this measurement, the tester is connected
between the frame of the machine and one of the windings. The frame and the two phases not
measured are earthed; see Figure 7-7 Connections of the stator windings for insulation
resistance measurements.
When phases are measured separately, all star-points of the winding system must be removed. If
the star-point of the component cannot be removed, as in a typical tri-phase voltage transformer,
the whole component must be removed.
3BFP 000 050 R0101 REV E