Manual for High Voltage Process Performance Motors
Maintenance - 61
3BFP 000 063 R0101 REV D
NOTE: As a thumb rule, an insulation resistance test should be made once a year. This should
suffice for most machines in most operating conditions. Other tests should only be
conducted if problems arise.
A maintenance program for the complete machine, including windings, is presented in Chapter
7.3 Maintenance program. This maintenance program however, should be adapted to the
customer's particular circumstances, i.e. servicing of other machines and operating conditions as
long as recommended servicing intervals are not exceeded.
7.6.3 The correct operating temperature
The correct temperature of the windings is ensured by keeping the exterior surfaces of the
machine clean, by seeing to the correct operation of the cooling system and by monitoring the
temperature of the coolant. If the coolant is too cold, water may condense inside the machine.
This can wet the winding and deteriorate the insulation resistance.
The stator operating temperatures must be monitored with resistance temperature detectors.
Significant temperature differences among the detectors could be a sign of damage in the
windings. Make sure that the changes are not caused by the drifting of the measuring channel.
7.6.4 Insulation resistance test
During general maintenance work and before the machine is started up for the first time or after
a long period of standstill, the insulation resistance of stator and rotor windings must be
measured.
The insulation resistance measurement provides information about the humidity and dirtiness of
the insulation. Based upon this information, correct cleaning and drying actions can be
determined.
For new machines with dry windings, the insulation resistance is very high. The resistance can,
however, be extremely low if the machine has been subjected to incorrect transportation and
storage conditions and humidity, or if the machine is operated incorrectly.
NOTE: Windings should be earthed briefly immediately after measurement in order to avoid
risk of electric shock.
7.6.4.1 Conversion of measured insulation resistance values
In order to be able to compare measured insulation resistance values, the values are stated at
40°C. The actual measured value is therefore converted to a corresponding 40°C value with the
help of the following diagram. The use of this diagram should be limited to temperatures fairly
near to the standard value of 40°C, since large deviations from it could result in errors.
