Insulation Resistance Measurement For Auxiliaries - ABB AMA Manual

Manual for High Voltage Process Performance Motors

7.6.5 Insulation resistance measurement for auxiliaries

64 - Maintenance
• 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 7-3 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 7-3 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 7-3 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.
a)
Figure 7-3 Connections of the stator windings for insulation resistance measurements
a) Insulation resistance measurement for star connected winding
b) Insulation resistance measurement for delta connected winding
c) Insulation resistance measurement for one phase of the winding. The 'M
insulation resistance meter.
After the insulation resistance measurement the winding phases must be earthed briefly in order
to discharge them.
To ensure correct operation of the machines protections and other auxiliaries, their condition
can be determined by an insulation resistance test. The procedure is described in detail in
Chapter 7.6 Maintenance of stator and rotor windings. The test voltage for the space heater
should be 500 VDC and for other auxiliaries 100 VDC. The insulation resistance measurement
for Pt-100 detectors is not recommended.
b)
MΩ
c)
MΩ
Ω
' represents the
3BFP 000 063 R0101 REV D
MΩ