NORD Drivesystems B1092 - Manual (Page 5)

www.nord.com B1092-GB -5-
3. Notes
For tightening torques of screw connections of the electrical connections and terminal board
connections (except for the terminal bar) see Fig. 4.
3.6 Checking the insulation resistance
Prior to the initial commissioning of the motor after a long period of storage or standstill
(approx. 6 months) the insulation resistance of the windings must be checked.
During and immediately after the measurements, the terminals have voltages which can be
dangerous, and must not be touched.
Insulation resistance
 The minimum insulation resistance of new, cleaned or repaired windings against earth
is 10 M Ω.
 Initially, the critical insulation resistance R
krit
is calculated. The calculation is made by
multiplying the measured voltage U
N
, e.g. 0.69 kV AC, with the constant factor (0.5 M Ω /kV):
R
krit
= 0.69 kV x 0.5 M Ω /kV =0.345 MΩ
Measurement:
The minimum insulation resistance of the winding against earth is measured with 500 V DC.
The temperature of the windings should be 25°C ± 15°C.
The critical insulation resistance must be measured with the windings at operating
temperature using 500 V DC.
Testing:
If for new or cleaned windings or repaired motors, which have been stored or not used for
long periods, the minimum insulation resistance of the winding against earth is less than 10
M
Ω, this may be caused by moisture. The windings must then be dried.
After long periods of operation the minimum insulation resistance may fall to the critical
insulation resistance. As long as the measured value does not fall below the calculated value
for the critical insulation resistance, operation of the motor may continue. If this value is fallen
below, the motor must be switched off immediately. The cause of this must be established
and if necessary the windings or parts of the windings must be repaired, cleaned or
dried.
3.7 Commissioning
NOTE: Electromagnetic compatibility
Production of interference: Great differences of torque (e.g. when driving a piston
compressor) induce a non-sine wave motor current, whose harmonics can cause an
impermissible effect on the mains and therefore impermissible production of interference.
With supply by frequency inverters, various strengths of interference are produced according
to the design of the frequency inverter (type, interference suppression, manufacturer). The
EMC information of the inverter manufacturer must be observed. If a shielded motor supply
cable is recommended, the shielding is most effective if a large area is electrically connected
to the metal terminal box of the motor (with metal screw connectors). With motors with
integrated sensors (e.g. thermistors) interference voltages due to the inverter may be
produced in the sensor cables.
Interference immunity: For motors with integrated sensors (e.g. thermistors) the operator
must ensure adequate immunity to interference by the selection of a suitable sensor cable
(possibly with screening, with connection as for the motor supply cable) and evaluation
device.
When operating motors with inverters at higher speeds than the nominal speed, the
mechanical limiting speed (Safe operating speed IEC 60034-1) must be observed (max. 3000
1
/
min
).