KSB SuPreme Series, Installation & Operating Manual

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6 Commissioning/Start-up/Shutdown
28 of 52
KSB SuPremE
6 Commissioning/Start-up/Shutdown
6.1 Checking insulation resistance
Prior to commissioning and following prolonged storage or standstill periods, the
insulation resistance will need to be checked and verified.
DANGER
Hazardous voltage
Danger of death from electric shock!
▷ Have all work performed only by qualified specialist personnel and only when
the drive is at a standstill and secured against unintentional start-up. This also
applies to auxiliary circuits (e.g. standstill heater).
▷
The drive must not be electrically connected at any point in time when work is
performed on the open terminal box.
DANGER
Hazardous voltage at the terminals
Risk of fatal injury due to electric shock!
▷
Ensure that no line supply voltage can be applied if any supply feeder cables
are connected.
▷
After you measure and determine the insulation resistance, discharge the
winding by connecting it to earth potential.
Table 22: Limit values for minimum insulation resistance and critical insulation
resistance of the stator winding
Rated voltage V
N
< 1 kV
Measuring voltage 500 - 1000 V
Minimum insulation resistance for new,
cleaned or reconditioned windings 200 MΩ
Critical specific insulation resistance after
a long operating time 0,5 MΩ / kV
▪ The insulation resistance can be optimally measured at 25 °C.
If the measurement is taken at ≠ 25 °C, the measurement result must be
converted to the reference value at 25 °C so that a comparison can be made with
the data in the table above.
– The insulation resistance halves for every 10 °C increase in temperature.
– The insulation resistance doubles for every 10 °C decrease in temperature.
▪ Dry, as-new windings typically have insulation resistances over 100 to 2000 MΩ,
depending on the size of the winding, the variant and the rated voltage.
– If the insulation resistance is close to the minimum value, the cause could be
moisture and/or contamination.
▪ During operation, the insulation resistance of the windings can fall to the critical
level because of environmental and operational factors.
– For a winding temperature of 25 °C, the critical insulation resistance can be
determined by multiplying the rated voltage (kV) by the specific critical
resistance value (0.5 MΩ/kV).
Example: Critical resistance for rated voltage
V
N
= 400 V: 400 V × 0.5 MΩ/kV = 0.2 MΩ
ü
Observe the operating manual for the insulation tester used.
1. Remove any connected main circuit cables from the terminals.
2. Measure the insulation resistance between the winding and the motor housing
at a winding temperature of 25 °C if possible. Other values apply to the
insulation resistance for different temperatures.